domain: sdv chim

text:
Mahery Andriamanantena

Shamsia Pithon

Manon Dijoux

Marine Hoareau

Christian Fontaine

Johnny Ferrard

Christophe Lavergne

Thomas Petit

Yanis Caro

A survey on the potential contribution of Reunion Island dye plant species diversity to the market demand for bioactive plant-based dyes and pigments

Keywords: Ethnobotany, Reunion Island, Dye plants, Pigments, Natural colorants

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The hazardous effects of artificial dyes on human health like carcinogenic or mutagenic activity [START_REF] Adeel | Sustainable application of microwave assisted extracted tea based tannin natural dye for chemical and bio-mordanted wool fabric[END_REF], and the contamination of the environment caused by wastewater discharged by dye industry [START_REF] Adeel | Ecofriendly application of coconut coir (Cocos nucifera) extract for silk dyeing[END_REF] led the industries to search new sustainable and less harmful dye sources [START_REF] Hussaan | Microwaveassisted sustainable exploration of cocklebur leaves (Xanthium strumarium L.) as a novel source of distinct yellow natural colorant for dyeing cotton fabric[END_REF]. Natural dyes are more environment-friendly than artificial dyes and may have biological benefits [START_REF] Batool | Sustainable natural coloring potential of bitter gourd (Momordica charantia L.) residues for cotton dyeing: innovative approach towards textile industry[END_REF]. Therefore, the natural dye market segment has emerged and has become increasingly important in global financial markets and linked with other important global issues. The global dyes and pigments market size was estimated from US dollars (USD) 29 to 36 billion in 2021, whereas the global market of naturally derived dyes and pigments (mineral and organic pigments) was valued at USD 5 billion, i.e., from 14 to 17% of the value of the global market [START_REF] Deuil | Etude de positionnement de la production et de l'usage de pigments et colorants naturels à partir de ressources d'origine végétales de l'Ile de la Réunion[END_REF]. The European market of natural dyes and pigments is valued at USD 1 billion in 2021, and the plant-based dye and pigments represented 70% of this European market in terms of financial income, i.e., USD 559 million. France, the third largest European producer of naturally derived dyes and pigments, after Germany and Italy, has a production of 49.4 million euros (9% of the entire production of natural dyes and pigments in this European market) [START_REF] Deuil | Etude de positionnement de la production et de l'usage de pigments et colorants naturels à partir de ressources d'origine végétales de l'Ile de la Réunion[END_REF]. However, despite the high demand from consumers, the natural dye industry faces some technical and sourcing issues. The application of natural dyes remains limited because of their somewhat restricted color range, low levels of color-fastness compared with artificial dyes, low levels of purity, low yield, instability and sensitivity to many environmental conditions, the raw material availability and the high cost of their production [START_REF] Andriamanantena | Malagasy Dye Plant Species: A Promising Source of Novel Natural Colorants with Potential Applications -A Review[END_REF]. To overcome these limits, researches for more sustainable products should involve the development of environmentally friendly production processes and the exploitation of new alternative sources of colorants, such as microbial pigments which become interesting by their sustainable production, biodegradable and coloring properties [START_REF] Dufossé | Filamentous fungi are large-scale producers of pigments and colorants for the food industry[END_REF][START_REF] Caro | Pigments and Colorants from Filamentous Fungi[END_REF].

Some plants are excellent raw materials for producing natural colorants as they have a great amount of watersoluble dyes or plant pigments, like dye plants such as indigo and madder [START_REF] Cardon | Le monde des teinture naturelles[END_REF], while others just don't seem to have enough pigments. Dye-producing plants possess a wide spectrum of utilization and they are an interesting group of alternative crops, providing that they will be cultivated and exploited in a sustainable way [START_REF] Andriamanantena | Malagasy Dye Plant Species: A Promising Source of Novel Natural Colorants with Potential Applications -A Review[END_REF]. Some natural colorants, such as carotenoids, flavonoids, hydroxyanthraquinones, etc., extracted from plants are promising dyestuffs and have regained popularity in a wide range of industries. They are widely used as coloring bioactive substances in several manufactured products, including textiles, cosmetics, food, pharmaceutical, plastics, paint, ink, paper and electronics (e.g., for dye-sensitized solar cells) industries [START_REF] Batool | Sustainable natural coloring potential of bitter gourd (Momordica charantia L.) residues for cotton dyeing: innovative approach towards textile industry[END_REF][START_REF] Cardon | Le monde des teinture naturelles[END_REF][START_REF] Fazal-Ur-Rehman | Environmentally friendly bio-dyeing of silk using Alkanna tinctoria based Alkannin natural dye[END_REF] due to their optical properties and additional biological (e.g., antioxidant, antibacterial, antiviral, and antifungal) activities [START_REF] Adeel | Sustainable extraction of colourant from harmal seeds (Peganum harmala) for dyeing of bio-mordanted wool fabric[END_REF][START_REF] Adeel | Environmental friendly exploration of cinnamon bark (Cinnamomum verum ) based yellow natural dye for green coloration of bio-mordanted wool fabric[END_REF][START_REF] Sanda | Natural dye extraction and dyeing of different fibers: a review[END_REF]. Thus, the coloring property as well as the added nutritional or therapeutic potentialities of some plant-based dyes and pigments make the biomaterials an important agricultural operation that have the potential to face the challenges of substitution of artificial colorants with the colored biocomponents extracted from different plant parts (seeds, fruit, flowers, stems, barks or adventive roots).

Dye plants can be found in a wide range of vegetation types, growing areas and climates, like in temperate forests and tropical forests. The sustainable exploitation of selected dye plants would make it possible to palliate certain diseases and environmental pollutions induced by the use of artificial colorants, to improve the agricultural income of the local populations practicing its culture, to create opportunity for business and farmers, and to offer to the selected dye-plant species a visibility for agricultural valorization of their extracted colored biocomponents [START_REF] Andriamanantena | Alternative sources of red dyes with high stability and antimicrobial properties: towards an ecological and sustainable approach for five plant species from Madagascar[END_REF].

From that perspective, Reunion Island located in the southwest of Indian Ocean is a good candidate as it counts among the world's top biodiversity hotspots with an endemic rate approximately of 40% [START_REF] Myers | Biodiversity hotspots for conservation priorities[END_REF]. Its plant biodiversity results from the colonization of species from Madagascar, Africa, Asia, India and Australia. For instance, many indigenous species from Reunion Island have been demonstrated to have medicinal properties and around 20 species have recently been incorporated in the French pharmacopeia [START_REF] Amédée | Plantes médicinales de La Réunion inscrites à la Pharmacopée française[END_REF]. Nevertheless, to the best of our knowledge, the dye-producing plant species diversity in Reunion Island had not been documented to date. No specific data are available on plants potentially rich in dyes or pigments in this island.

Hence, this original research study aims, for the first time, to inventory all the dye-producing plants or plant species potentially rich in dyes or pigments from the endemic, native, introduced and alien-invasive plants growing in Reunion Island. Firstly, an ethnobotanical survey focused on the uses of plants traditionally used for dyeing in Reunion Island was conducted. Then, we developed an assessment scoring system that used different criteria to evaluate and assign each plant a "dye score, " to finally select the most promising species which have been further harvested from eight growing areas in Reunion Island and investigated in detail for their coloring property and application in textile dyeing.

Materials and methods

Study area

Reunion Island (55° 3′ E and 21° 5′ S), with Mauritius and Rodrigues, is one of three islands that composes the Mascarenes located in the southwest of Indian Ocean. It is the only European region in the southern hemisphere. Reunion Island is a French overseas department and divided into 116 municipalities. The population is mainly composed of people originated from France, Africa, Madagascar, India and China. This is a relatively small tropical island, approximately 2500 km 2 . Economic activities and about 80% of the population are located in the coastal lowlands due to the rugged topography of the island which was created two million years ago by the emergence of a submarine volcano. This particular formation has been considered as the main factor that give to this island the high endemism of growing plant and animal species [START_REF] Myers | Biodiversity hotspots for conservation priorities[END_REF]. Almost 40% of the territory belongs to the National Park, which was established to preserve and conserve the terrestrial biodiversity.

Exploration of the Reunion island dye plant species biodiversity

The ethnobotanical survey of the dye plant species biodiversity of Reunion Island was conducted by botanists of the Conservatoire Botanique National des Mascarins (CBNM) in Reunion island. A literature review was conducted by consulting the available documents on the history and plant diversity of Reunion Island at the University of Reunion and the CBNM libraries. The works of Boullet et al. (1886[START_REF] Boullet | Index de la flore vasculaire de La Réunion (Trachéophytes) : statuts, menaces et protections[END_REF] in "Index des Tracheopytes" [START_REF] Boullet | Index de la flore vasculaire de La Réunion (Trachéophytes) : statuts, menaces et protections[END_REF], Jacob de Cordemoy (1895), the "Flore des Mascareignes" written by Bosser et al. (1935[START_REF] Bosser | Flore des Mascareignes[END_REF][START_REF] Bosser | Flore des Mascareignes[END_REF][START_REF] Bosser | Flore des Mascareignes[END_REF] [START_REF] Bosser | Flore des Mascareignes[END_REF][START_REF] Bosser | Flore des Mascareignes[END_REF][START_REF] Bosser | Flore des Mascareignes[END_REF] or [START_REF] Lavergne | [END_REF][START_REF] Lavergne | Fleurs de Bourbon[END_REF]Lavergne ( , 1996) ) [START_REF] Lavergne | [END_REF][START_REF] Lavergne | Fleurs de Bourbon[END_REF], amongst others, allowed us to inventory most of the Reunion Island dye-producing plant species or plant species identified as potentially rich in dyes or pigments. Several online documentation and database focused on ethnobotany, chemistry, biodiversity, dyes and pigments or medicinal plants have been as well consulted. Furthermore, all the information obtained from the reviewed literature has been combined and supplemented by information obtained from the ethnobotanical survey of Reunion Island's dye plants conducted by a team leaded by Christophe Lavergne from CBNM. This survey from January 2021 to November 2022 relied on the local peoples and stakeholders who have a good knowledge of the history and culture of Reunion Island including local dyers, farmers, small cosmetics manufacturers, botanists, etc. Ethnobotanical data were recorded via face-to-face interviews in the local language (Créole) or French, depending on the interviewee. The questionnaire concerned the knowledge of the traditional uses of some plant species as coloring materials, and the survey enabled us to inventory additional plant species traditionally uses in Reunion Island for natural dyeing. Ten questions, listed below, have been asked to each stakeholder: "

Scoring and evaluation of the most promising plant species for coloring applications

Following the assessment and survey of dye plant biodiversity, we developed an assessment scoring system that used different criteria to evaluate and assign each plant a "dye score" to determine the most promising plant species from Reunion Island for coloring applications. Using a scientific approach to the dye score, we established eight criteria and four indexes, which can be described as follows. The first six criteria (criteria 1 to 6) are based on empirical knowledge collected from the literature review and ethnobotanical survey of the considered plant species. The other two criteria (criteria 7 & 8) are based on laboratory experiments using a standardized, ecofriendly extraction process of dyes from the raw materials as previously described by the authors [START_REF] Andriamanantena | Alternative sources of red dyes with high stability and antimicrobial properties: towards an ecological and sustainable approach for five plant species from Madagascar[END_REF]. Each criterion is ranked on a scale from 1 to 10, where 1 is the lowest score meaning that the plant species has no or very weak interest related to this criterion and 10 is the highest, indicating that the species exhibits great potential related to this criterion. We have classified each criterion according to the "dye score" ranking definition developed in Table 1. Criterion 1 (C1) represents the "endemicity level" of the considered plant species on Reunion Island. On a scale of 1 to 10, the lowest score 1 was given to exotic and introduced species; 3 to the native and cryptogenic plants; 7 to the Mascarenes regional endemic species in the Indian Ocean; and 10 was given only to the Reunion Island endemic species.

Criterion 2 (C2) represents the scientific knowledge currently available on the considered plant species. As this assessment and survey of the dye plant species biodiversity of Reunion Island is intended to be innovative, the highest score 10 was given to the plant species which are still unknown to the scientific community (i.e., including those that are undescribed or are described but otherwise data deficient in literature). The lowest score 1 was given to perfectly described species with botanical and chemical data (known pigments, etc.). The intermediate scores 7 and 3 were given to relatively described species, with or without known information on coloring properties of the species.

Criterion 3 (C3) evaluates the accessibility and availability of the considered plant species in Reunion Island. Taking a conservation bio-diversity-centered approach, critically endangered, rare and/or protected plants that are difficult to access were given the lowest score 1. A score of 3 was given to the unprotected species that are accessible in protected areas with authorization; 7 to species that are abundant in the wild; and 10 to species currently cultivated in Reunion Island.

Criterion 4 (C4) represents the cultivability. A score of 1 was given to plants that are very difficult to grow; 3 to potentially cultivable but slow-growing plants; 7 to known cultivable plant; and 10 to the currently cultivated plants.

Criterion 5 (C5) ranked the botanical parts used for pigment extraction on a scale of 1 to 10, privileging the most renewable parts of plants. Thus, a score of 1 was given to the whole plant or the trunk, the harvesting of which would most likely kill the plant; 3 to the adventitious roots; 7 to the barks, fruits and flowers; and 10 when the leaves are used for coloring applications.

Criterion 6 (C6) ranked the industrial interests and known applications of the plant species, where 1 was given to the plants without any other known interests or uses (apart from their tinctorial interest); 3 to plants with one or two other known uses; 7 to the plants with three of four other uses; and 10 to the plants with more than five other known interests or uses.

Criterion 7 (C7) evaluated the color and stability of the dyes and pigments extracted from the plant species. Some colors are more interesting than others in terms of industrial applications, so they were assigned a higher score. A score of 1 was given to colorless extract obtained from the standardized dye extraction described below; 3 to the common brown, black, or beige hues or for a nonstable color; 7 to red, orange and yellow hues; and 10 for stable and unusual colors like blue, green and pink.

Criterion 8 (C8) rated the yield and difficulty of extraction. The highest score of 10 was given to dyes and pigments that were extracted easily and efficiently using the eco-extraction method with water and ethanol as solvents; 7 to plants containing pigments that are easy to extract with a mixture of water and ethanol but with a low yield (< extraction yield mean value for each collected plants part, w/w); 3 to plants containing pigments that are insoluble in a mixture of water and alcohol, or pigments that are difficult to extract using this sustainable process and therefore require non-eco-compatible organic solvents; and 1 to dye plants that need a transformation to express the coloration (i.e., by mordanting or fermentation).

Finally, four indexes were further calculated based on these eight criteria: [START_REF] Adeel | Sustainable application of microwave assisted extracted tea based tannin natural dye for chemical and bio-mordanted wool fabric[END_REF] The "Endemicity index" ( Iend ) was calculated by multiplying criterium C1 × C2; [START_REF] Adeel | Ecofriendly application of coconut coir (Cocos nucifera) extract for silk dyeing[END_REF] The "Cultivability index" ( Icult. ) was calculated by multiply- ing criteria C3 × C4; (3) The "Industrial extrapolation index" ( Iind. ) was calculated by multiplying criteria C5 × C6; and (4) The "Coloring strength index" ( Icol. ) was cal- culated by multiplying criteria C7 × C8. We have classified each index according to the "dye score" ranking definition developed in this study. Given that the hues, the yields and the difficulty of the color extraction were the most important criteria for coloring applications in industries, the "Coloring strength index" was counted two times more than the other indexes for each plant species final "dye score. " This "dye score" is calculated using the following formula:

where Endemicity index (Iend.) = C1*C2; Cultivability index (Icult.) = C3*C4; Industrial extrapolation index (Iind.) = C5*C6; Coloring strength index (Icol.) = C7*C8; and C1 is the endemic status, C2 is the scientific knowledge, C3 is the accessibility and availability, C4 is the cultivability, C5 is the botanical parts used for pigment extraction, C6 is the Industrial interests and other known applications of the species, C7 is the color and stability of dyes and pigments extracted, and C8 represents the yield and the difficulty of the color extraction.

Plant material collections

Around 60 interesting dye plant species selected from our assessment scoring system have been further harvested in different areas of Reunion Island as shown in The CBNM collection form was used for the traceability of each collection. Depending on the species, adventitious roots, barks, stems, leaves, flowers, fruits or lianas were collected. The harvesting was done according to good practices in order to reduce adverse effect on the plants. For example, in the case of bark and roots, a part was scraped off and then pine tar was sprayed on the cut to avoid external contamination. The quantity of fresh material to be collected varies according to the part of the plant concerned. Thus, the ideal proportions to be collected to ensure a sufficient quantity of fresh material for pigment extraction were estimated at 500 g for barks and roots, 1 000 g for leaves and flowers, and 2 000 g for fruits. Plant organs were collected from three different trees or shrubs from the same geographical and geological area, and they were then mixed to constitute one representative collection batch. The collection was repeated three times. Each collection batch undergoes various pre-treatments before pigment extraction, including cutting, drying and grinding. All samples were firstly cut into small pieces. Two different drying methods have been used: freeze-drying (Labconco freezone2.5) used in the case of fruits (due to high moisture content and nutrients that may favor the development of molds during slow drying), and for drying leaves, bark or roots with low moisture content, the drying was carried out at 45 °C using a climatic chamber (Memmert HPP410) with a relative humidity controller set at 10% in order to achieve a slow drying process to avoid damage on the plant like browning and chemical reactions, due to a high temperature. Duration of the drying process varies according to the initial moisture content, generally ranging from a few days to a week. Then, the sample was coarsely ground with a mill (Retsch SM100) and finely ground with a laboratory mixer (Kinematica Microtron MB550) to finally obtain a powder that will be kept away from light and humidity at 4 °C before the extraction stage.

Pigment extractions and evaluation of coloring properties of the plant-based dyestuffs

Pigment extraction have been performed using the methods described previously by the authors [START_REF] Andriamanantena | Alternative sources of red dyes with high stability and antimicrobial properties: towards an ecological and sustainable approach for five plant species from Madagascar[END_REF]. Briefly, a pressurized liquid extraction (PLE) under nitrogen was applied with a mixture of ethanol and water (70/30, v/v) by using an accelerated solvent extractor (ASE ™ 350, Accelerated Solvent Extractor, Dionex). About 10 g of dry plant materials are mixed with diatomaceous earth to fill a 34 ml ASE cell. Conditions were as follows: temperature, 45 °C; pressure, 110 bars; three cycles with static extraction time of 3 min; purge time 2 min; and flush volume 100%. The procedure was performed three times under repeatability conditions. Then, the crude extracts were concentrated on a centrifugal evaporator (Genevac EZ2 +) at 45 °C under vacuum, resolubilized on a small volume of the same extraction solvent to be finally lyophilized (Labconco freezone2.5) during 48 h in order to generate crude dry color extract in powder (i.e., the plant-based dyestuff ) for pigment extraction yield calculation. All extracts were kept at 4 °C until further use.

To check the coloring property of the dry color extracts, the sample was dissolved on the same solvent used for the extraction at different concentrations, i.e., from 1.0 to 32 mg/mL of dry powder extract in solution, to show the evolution of the shade of the sample by their color value measured in the international CIELab color system in terms of L* (lightness), a* (greenness versus redness), and b* (blueness versus yellowness). The color coordinates were analyzed using a spectrophotometer (Konica Minolta CM-3600A) with 10 mm pathlength quartz cuvette, combined to the color data software SpectraMagic NX (Konica Minolta) for data analysis.

Furthermore, optical density of the sample has been measured with a spectral scanning from 200 to 800 nm by an UV-visible spectrophotometer (Thermo Scientific Genesys 10S). The same solvent used for the extraction and dilution was used as a blank. To check the solubility in water and the stability of the colored extracts toward pH and temperature variations, materials were dissolved at 4 mg/ml in Britton-Robinson water buffer solutions of pH 4, pH 7 and pH 10, and then exposed to different temperatures from 25 to 95 °C using a water-bath. The exposition time was from 4 to 24 h.

Then, the dyeing property of the plant extract has been checked for bath-dyeing wool and cotton fibers with different mordants: 1-potassium alum + potassium bitartrate mordant; 2-aluminum acetate mordant; 3-aluminum acetate mordant + tannins (gallnut); 4-aluminum acetate + ferrous sulphate mordant; 5-aluminum acetate + tannins (gallnut) + ferrous sulphate mordant; 6-aluminum acetate mordant + ash lye + sodium carbonate.

Statistical analysis

The statistical analysis for each experiment was performed using analysis of variance (ANOVA) and expressed as mean ± standard deviation of three replicates. The procedure was followed by Duncan test to determine the statistical significance (p < 0.05).

Results and discussion

Ethnobotanical survey of plants traditionally used in natural dyeing on Reunion Island

In mid-1600 s, the Reunion Island was first settled by French colonist. They bring slaves from Madagascar, Africa India, and Asia to work first in cane and coffee plantation. Slaves brought with them some medicinal and other plants traditionally used in their country. Progressively, many new plant species were introduced by people from all walks of life. People bring some traditional knowledge and know-how notably in the field of dyeing textile from Madagascar [START_REF] Fee | Recipes from the past: Highland textile dyes in 19th century Merina sources, with a translation of passages from the "Ombiasy"s manuscript[END_REF][START_REF] Etheve | Manuel de teinture naturelle : Exemple de Madagascar[END_REF], and some dye-producing plants were probably introduced at that time. The evolution of indigenous species, far from their region of origin, led to the emergence of several endemic species [START_REF] Lavergne | Le grand livre des tisaneurs et plantes médicinales indigènes à la Réunion[END_REF]. In this study, the assessment of the Reunion Island's plant biodiversity through the "PLANTIN" project (co-funded by European Regional Development Fund) allowed us to establish the first ethnobotanical inventory of plants growing on Reunion Island which may have promising properties as a new alternative source of dyes or pigments for the industries.

Local people from Reunion Island has accumulated traditional knowledge of dyeing plants and their uses over the years. This approach had been discontinued in Reunion, in comparison with Madagascar, where a rich ancestral knowledge of dye plants has been described and transmitted from generation to generation [START_REF] Andriamanantena | Malagasy Dye Plant Species: A Promising Source of Novel Natural Colorants with Potential Applications -A Review[END_REF][START_REF] Andriamanantena | Alternative sources of red dyes with high stability and antimicrobial properties: towards an ecological and sustainable approach for five plant species from Madagascar[END_REF][START_REF] Etheve | Manuel de teinture naturelle : Exemple de Madagascar[END_REF]. The oldest trace of the uses of dye plants in Reunion Island seems to come from Indigofera plantations in the north of the island, which was abandoned a long time ago. The uses of Curcuma longa locally called "saffran péï" have been cited several times during the survey. Considering that this plant is very present in the Indian culture, it is not surprising to see the extent of this plant in different uses in Reunion Island including natural dyeing as his history is attached in great part to the Indian culture. The third most famous dye plants in the island is the famous endemic species Weinmannia tinctoria Sm., locally called "Tan rouge" (red "tan") [START_REF] Imhaus | Notice sur les principales productions naturelles et fabriquées de cette île : Réunion[END_REF]. While bark of this last specie was cited several times in the literature review and during the ethnobotanical surveys as used traditionally for tanning application in Reunion, no scientific data are really available on its utilization for tanning applications over the world. Furthermore, there is evidence that this natural dyeing with plant-based textile dyes has not been abandoned uniformly in Reunion Island, particularly in recent years. Craftsmen and small companies working in textiles have tried to reintroduce dye plants from some alien-invasive species in Reunion Island into their dyeing process (i.e., for the formulation of traditional dye baths in hot water). For instance, "WHOLE, " "Kouleur local, " and "Nuance de Couleurs" are examples of companies that are recently working on natural dyeing from some Reunion Island's dyestuffs of plant origin. As the reuse of alternative sources of colorants including dye plants has grown considerably these last decades, this new trend can contribute to the conservation of some species as the example of Weinmannia tincoria. Actually, W. tinctoria was famous for its dyeing properties and known by most of the local population. Due to its non-use, it has been replaced by other species and has been considered as an endangered species lastly by the International Union for Conservation of Nature (IUCN). This a great example of the loss of some traditional knowledges in Reunion Island and the importance of its conservation as it can also preserve some species to not disappear. If it will be used as dyeing sources or for further uses in the following years, it's sure that it will be planted again by local population or even in industrial scale.

From the literature review and ethnobotanical surveys focused on uses of plants traditionally used in dyeing and conducted from local elderly informants between January 2021 to November 2022, a list of 194 plant species (72 botanical families, and 157 plant genera) with diverse botanical status (endemic, native, introduced or alien-invasive species) have been inventoried. The entire list of 194 plant species can be found as Additional file 1: Table S1. It demonstrated the potential of these plant species as new sources of water-soluble dyes or pigments, including the endemicity, the IUCN (International Union for Conservation of Nature) and/or the protected status of the species in Reunion Island, the accessibility, the cultivability, the plant organs used for the extraction process, the colors that may be extracted, the scientific knowledge, the industrial interests and current uses of these plant species, amongst others. Dye plants inventoried here include 34 endemic species, 22 native and cryptogenic species, and 138 introduced species (including 37 alien-invasive species) which may have promising properties as new alternative crops for producing bioactive dyes and pigments for the industries.

The uses of endemic plant species in Reunion Island potentially rich in dyes or pigments

A total of 13 endemic plant species to Mascarenes, 12 plant species strict endemic species to Reunion Island have been mentioned as having potential traditional uses as sources of dyestuff materials. The botanical information and the coloring properties of all inventoried endemic plant species in Reunion Island potentially rich in dyes or pigments are described in Table 2. Some of them were mentioned in the literature as plants formerly used in textile dyeing, e.g., tanins extracted from wood of Indigofera ammoxylum [START_REF] Polhill | Flore des Mascareignes : La Réunion, Maurice, Rodrigues. Mauritius, Sugar Industry Research Institute[END_REF] and Foetidia mauritiana [START_REF] Friedmann | Lécythidacées. Flore des Mascareignes, la Réuion[END_REF], tanins from barks of Weinmannia tinctorial [START_REF] Imhaus | Notice sur les principales productions naturelles et fabriquées de cette île : Réunion[END_REF][START_REF] De Lanessan | Les plantes utiles des colonies françaises (Edition 1886[END_REF][START_REF] Cordemoy | L'île de La Réunion (Phanérogames ; Cryptogames vasculaires, Muscinées) avec l'indication des propriétés économiques et industrielles des plantes[END_REF], Mimusops balata [START_REF] Imhaus | Notice sur les principales productions naturelles et fabriquées de cette île : Réunion[END_REF], and Terminalia bentzoe subsp. bentzoe [START_REF] Imhaus | Notice sur les principales productions naturelles et fabriquées de cette île : Réunion[END_REF][START_REF] Cordemoy | L'île de La Réunion (Phanérogames ; Cryptogames vasculaires, Muscinées) avec l'indication des propriétés économiques et industrielles des plantes[END_REF] bluish-brown colors from fruits of Bertiera borbonica and Bertiera rufa [START_REF] Lavergne | [END_REF], and pigments from stem and leaves of Psychotria borbonica [START_REF] Lavergne | Fleurs de Bourbon[END_REF][START_REF] Imhaus | Notice sur les principales productions naturelles et fabriquées de cette île : Réunion[END_REF][START_REF] Cordemoy | L'île de La Réunion (Phanérogames ; Cryptogames vasculaires, Muscinées) avec l'indication des propriétés économiques et industrielles des plantes[END_REF].

On the other hand, the traditional uses of some endemic plants as textile dyestuffs have only been identified from the ethnobotanical survey conducted here, such as the uses of bark of Ochrosia borbonica (locally called "bois jaune"-yellow wood), the barks and stems of Erythroxylum laurifolium, the flowers of Hypericum lanceolatum, the leaves of Latania lontaroides, the bark of Monimia ovalifolia, and Sophora denudata, amongst others.

Some of these endemic species are classified by the International Union for Conservation of Nature (IUCN) as Vulnerable (VU), Endangered (EN), or Critically Endangered (CR). For example, eight endemic species inventoried here are protected in Reunion Island by local environmental legislation, e.g., Indigofera ammoxylum (CR), Foetidia mauritiana (CR), Ruizia cordata (CR), Latania lontaroides (CR), Terminalia bentzoe subsp. bentzoe (CR), Aloe macra (EN), Sophora denudata (EN), and Ochrosia borbonica (VU). Interestingly, L. lontaroides and T. bentzoe subsp. Bentzoe-both classified as CR by IUCN-are two species widely available and easily cultivated in Reunion Island. Thus, they may have promising interests as local sources of natural dyes or pigments for the industries. Edible fruits of L. lontaroides contain oil seeds with very similar composition to that of the edible palm oil [START_REF] Caro | Chemical characterization of unconventional palm oils from Hyophorbe indica and two others endemic Arecaceae species from Reunion Island[END_REF] but the coloring properties of the species have never been described in the literature. Barks of T. bentzoe subsp. bentzoe have interesting biological properties like antioxidant and cytotoxic activities [START_REF] Apel | N-myristoyltransferases inhibitory activity of ellagitannins from Terminalia bentzoë (L.) L. f. subsp. bentzoë[END_REF]. The barks of this plant are rich in tannins and can be used to dye natural fibers with a black or yellow color, depending on the mordant used during natural dyeing [START_REF] Bosser | Flore des Mascareignes[END_REF][START_REF] Imhaus | Notice sur les principales productions naturelles et fabriquées de cette île : Réunion[END_REF][START_REF] Cordemoy | L'île de La Réunion (Phanérogames ; Cryptogames vasculaires, Muscinées) avec l'indication des propriétés économiques et industrielles des plantes[END_REF][START_REF] Rummun | Terminalia bentzoë, a mascarene endemic plant, inhibits human hepatocellular carcinoma cells growth in vitro via G0/G1 phase cell cycle arrest[END_REF].

On the other hand, the bark of the endemic species O. borbonica has been exploited without a sustainable policy and almost led to the extinction of this species in the Mascarenes. This plant species has been used by local population for its medicinal properties against malaria and fever many years ago. Only a few trees have been recently inventoried in Reunion Island and the species are locally protected. The health benefits of O. borbonica have been proven by the most recent pharmacological research [START_REF] Zhang | Alkaloids from Ochrosia borbonica[END_REF][START_REF] Nirmala | Natural plant resources in anti-cancer therapy[END_REF][START_REF] Liu | Ochroborbone, A New Cytotoxic Indole Alkaloid from Ochrosia borbonica[END_REF][START_REF] Suroowan | A comprehensive review of ethnopharmacologically important medicinal plant species from Mauritius[END_REF]. Thus, the bark of O. borbonica can produce a yellow dyestuff rich in bioactive alkaloids with therapeutic activities. It would be interesting to relaunch the study on public and/or private partnership reforestation projects with this promising but endangered plant, O. borbonica. It may led to the conservation of this highly-valued species rich in bioactive yellow dyes. Furthermore, even if the species W. tinctoria is classified as endangered in some parts of the world by IUCN, this tree is not locally protected and very common in Reunion Island (in the wild and private gardens). It is used as an ornamental plant. The plantation of this species has resumed recently to support the specific honey production from Reunion Island called "miel vert" honey). The bark of W. tinctoria has been used for its dyeing properties to dye leather in red color a long time ago. It is a source of tannins [START_REF] De Lanessan | Les plantes utiles des colonies françaises (Edition 1886[END_REF]. However, very limited information is available on the coloring properties and dye composition of the dyestuffs extracted from bark of W. tinctoria, and it may become an important and interesting topic for future research on natural dyeing from tropical dye plants.

Finally, other recorded endemic species, not protected and widely available in the island (Table 2), such as fruits of Olax psittacorum (locally called "corce rouge"), Bertiera rufa, Erythroxylum laurifolium, Hypericum lanceolatum, Monimia ovalifolia, Weinmannia mauritiana, etc., also represent an interesting group of alternative crops for natural dyeing application, if they will be exploited in a sustainable way by local population.

The uses of native plant species in Reunion Island potentially rich in dyes or pigments

All the inventoried native and cryptogenic plant species in Reunion Island potentially rich in dyes or pigments are described in Table 3. Among the 23 species listed below, many of them are also growing in Madagascar [START_REF] Andriamanantena | Malagasy Dye Plant Species: A Promising Source of Novel Natural Colorants with Potential Applications -A Review[END_REF][START_REF] Cardon | Le monde des teinture naturelles[END_REF][START_REF] Etheve | Manuel de teinture naturelle : Exemple de Madagascar[END_REF] and inventoried as dye-producing plants, as the example of Thespesia populnea Danais fragrans [START_REF] Cardon | Le monde des teinture naturelles[END_REF], and Morinda citrifolia [START_REF] Bussmann | Anthraquinone Content in Noni (Morinda citrifolia L.). Evidence-Based Complementary and Alternative Medicine[END_REF][START_REF] Dhingra | Dyeing with Morinda citrifolia: In Pursuit of Sustainable future[END_REF][START_REF] Rahman | Extraction of natural dye powder from morinda citrifolia and its application as antibacterial dyes for cotton fabrics[END_REF]. The cryptogenic species T. populnea (Malvaceae; locally called 'Porché') is widely and easily cultivated in Reunion Island, and should be used as an efficient alternative source of reddish natural dyestuffs [START_REF] Andriamanantena | Malagasy Dye Plant Species: A Promising Source of Novel Natural Colorants with Potential Applications -A Review[END_REF][START_REF] Mohini | Dataset on analysis of dyeing property of natural dye from Thespesia populnea bark on different fabrics[END_REF][START_REF] Manisha Kothari | Quantification of Phytoconstituents and Isolation of Flavonoids from Thespesia populnea Bark Extracts[END_REF][START_REF] Kumaresan | Dyeing of Cotton Fabric with Natural Dye obtained From Flower of Thespesia Populnea using Combination of Mordants[END_REF][START_REF] Amutha | Dyeing of textiles with natural dyes extracted from Terminalia arjuna and Thespesia populnea fruits[END_REF]. D. fragrans (locally called 'Liane jaune'-yellow liana) and M. citrifolia (noni, or locally called 'malaye') are native plant species from the Rubiaceae family. The uses of roots as sources of anthraquinonoid dyes are common in this botanical family (like the case of the famous Rubia tinctorum) [START_REF] Derksen | Analysis of anthraquinones in Rubia tinctorum L. by liquid chromatography coupled with diode-array UV and mass spectrometric detection[END_REF]. The species M. citrifolia is widely available and easily cultivated in Reunion Island, whereas D. fragans is a relatively rare species in the wild, but the roots of these two Rubiaceae plants could be used for natural dyeing properties (yellowish to orangish-red) [START_REF] Andriamanantena | Malagasy Dye Plant Species: A Promising Source of Novel Natural Colorants with Potential Applications -A Review[END_REF][START_REF] Dhingra | Dyeing with Morinda citrifolia: In Pursuit of Sustainable future[END_REF].

The native species Leea guineensis (Vitaceae; locally called 'Bois de sureau') is a tree that is very common in wetlands in Reunion. Its rapid growth and strong regeneration capacities make it an invasive plant in the wild. The barks of this species are rich in flavonoids, tannins and terpenes [START_REF] Andriamanantena | Malagasy Dye Plant Species: A Promising Source of Novel Natural Colorants with Potential Applications -A Review[END_REF], and they could produce red dyes with tinctorial property. The same applies to terminal bud and leaves of the native cultivated species Pandanus utilis (Pandanaceae; locally called 'Vacoa') which contain bioactive components [START_REF] Lo | Constituents of the Leaves of Pandanus Utilis[END_REF] and could produce yellowish and greenish textiles dyes according the ethnobotanical data recorded here.

Furthermore, other inventoried native species (today not cultivated in Reunion, but easily accessible in wilderness area and not protected) should also be promising for natural dyeing application, such as liana of Cassytha filiformis (Lauraceae) for orangish-yellow colors; flowers and roots of Mussaenda arcuata (Rubiaceae) for orangish-red shades; barks of Pemphis acidula (Lythraceae) and Securinega durissima (Phyllanthaceae) for reddish shades; barks of Antirhea borbonica (Rubiaceae), leaves of and Phymatosorus scolopendria (Polypodiaceae) for greenish colors; or leaves and fruits of Pteridium aquilinum (Dennstaedtiaceae) for black shades. However, additional studies are necessary to confirm the pigment properties and tinctorial strength on natural fabrics of these uncharacterized tropical plants.

Introduced and alien-invasive species in Reunion Island potentially rich in dyes or pigments

Actually, Reunion Island contains several microclimates where the pedological properties and the climates vary from one area to one another. It explains that a multitude of species and botanical family of plants with wellknown dyeing properties are able to acclimatize to this island. Nevertheless, unlike the history behind dye plants sectors in Madagascar, this field of natural colorants and pigments have never been really developed in Reunion island. Traces of industrial plantation and uses of Indigofera tinctoria have been quoted during the ethnobotanical survey in the north of the island. Unfortunately, it has been replaced by other crops because at that time, natural colorants didn't have the current importance in the world market. 138 introduced species potentially rich in dyes or pigments have been listed, and most of them are cultivated in the island (see Table 4). Most relevant examples of the introduced cultivated plants rich in dyes or pigments are Curcuma longa [START_REF] Alafiatayo | Phytochemical evaluation, embryotoxicity, and Teratogenic effects of curcuma longa extract on zebrafish (Danio rerio)[END_REF][START_REF] Dinesh | Assessment of Cytotoxic, Antioxidant, Thrombolytic, Anti Inflammatory and Antimicrobial Activity of Curcuma longa Linn, Cissus quadrangularis and Boerhaavia diffusa Herbal Mixture -An In vitro Study[END_REF], Selenicereus undatus (syn. Hylocereus undatus; called 'Pitahaya') [START_REF] Ibrahim | Genus Hylocereus: Beneficial phytochemicals, nutritional importance, and biological relevance-A review[END_REF], Lawsonia inermis [START_REF] Bhuiyan | Coloration of polyester fiber with natural dye henna (Lawsonia inermis L.) without using mordant: a new approach towards a cleaner production[END_REF], Terminalia catappa [START_REF] Silva | A medicinal plant from the Caribbean pharmacopeia with anti-Helicobacter pylori and antiulcer action in experimental rodent models[END_REF][START_REF] Katiki | Terminalia catappa: Chemical composition, in vitro and in vivo effects on Haemonchus contortus[END_REF], Haematoxylum campechianum [START_REF] Lin | Chemical Constituents from the Heartwood of Haematoxylon campechianum as Protein Tyrosine Kinase Inhibitors[END_REF], and Casuarina equisetifolia [START_REF] Zhang | Antioxidant tannins from stem bark and fine root of Casuarina equisetifolia[END_REF][START_REF] Narayanaswamy | Natural dye from the bark of Casuarina equisetifolia for silk[END_REF], amongst others. The species C. longa and S. undatus are widely cultivated and used in the island for local foods [START_REF] Alafiatayo | Phytochemical evaluation, embryotoxicity, and Teratogenic effects of curcuma longa extract on zebrafish (Danio rerio)[END_REF][START_REF] Dinesh | Assessment of Cytotoxic, Antioxidant, Thrombolytic, Anti Inflammatory and Antimicrobial Activity of Curcuma longa Linn, Cissus quadrangularis and Boerhaavia diffusa Herbal Mixture -An In vitro Study[END_REF]. Interestingly, according to the ethnobotanical data recorded here, a large number of alien-invasive plants in Reunion are potentially rich in dyes or pigments, such as Leucaena leucocephala [START_REF] Campos | Chemical composition and nutritional value of leaves and pods of Leucaena leucocephala, Prosopis laevigata and Acacia farnesiana in a xerophilous shrubland[END_REF], Antigonum leptopus [START_REF] Kekuda | Medicinal Uses, Phytochemistry and Pharmacological Activities of Antigonon leptopus Hook. and Arn. (Polygonaceae)[END_REF], Acacia dealbata [START_REF] Linhares | LCA of textile dyeing with Acacia Dealbata tree bark: a case study research[END_REF], Casuarina equisetifolia [START_REF] Narayanaswamy | Natural dye from the bark of Casuarina equisetifolia for silk[END_REF], etc.

First selection and characterization of some promising dye plants in Reunion Island

Based on different criteria, like endemicity, scientific knowledge, accessibility and availability, cultivability, plant organs used for the extraction, and the industrial interests and other known applications of the species, we established a classification method to finally select the most interesting and widely available dye plant species listed above. From this first collection of Reunion Island's dye plants, we valued endemic and native dye plants because of their value to the extension and conservation of the Island plant biodiversity, and also for their potential as a locally available resource that can lead to regional economic development. Thus, 15 endemic and 13 native species (i.e., 58% of the endemic and native species inventoried below) have been harvested from different growing areas in Reunion Island. The results of our laboratory experiments in terms of extraction yield and coloring properties (shade, solubility and stability) of the colors that have been extracted from each dye plant harvested, as ranked by their 'dye score, ' are described in Table 5. Some colors are more interesting than others in terms of industrial dyeing applications, thus we valued rare/special colors (e.g., blue, magenta, pink, cyan, mauve, black…) as well as yellow, orange and red shades which are sought in the dyeing industries to replace synthetic azo dyes. Moreover, the colors extraction yield from the plant organs, and the capacity to obtain stable water-soluble dyes extracted easily and efficiently using eco-extraction method at low temperature with water or aqueous ethanolic solution as solvents are also two main factors contributing to the success of the industrial use of the considered plant-based dyestuffs. The species Thespesia populnea sets itself apart by its high dye score of 60 (from a scale of 1 to 100). This is the highest dye score obtained among all the endemic and native plant species inventoried in this study (Table 5). First, a value of 9 was attributed to the endemicity index (criteria C1*C2; Tab.1) considering that T. populnea is a cryptogenic species in Reunion and few information is available on the coloring properties of the flowers and fruits of this species [START_REF] Mohini | Dataset on analysis of dyeing property of natural dye from Thespesia populnea bark on different fabrics[END_REF][START_REF] Amutha | Dyeing of textiles with natural dyes extracted from Terminalia arjuna and Thespesia populnea fruits[END_REF][START_REF] Suvarna | A review on phytochemical and pharmacological properties of Thespesia populnea[END_REF]. However, only little information is available on the dyeing properties of the barks analyzed here, and the nature of the pigments from the red barks is not established. The cultivability index (criteria C3*C4; Tab.1) was scored at 100 because T. populnea is easily cultivated in the island, and the industrial extrapolation index (criteria C5*C6; Tab.1) presents the value of 49 because the barks are used to extract the dyes, and this plant species has other industrial interests in Reunion island (e.g., medicinal uses). Then, the coloring strength index, based on the criteria C7 (color and stability of dyes and pigments extracted) and C8 (yield and difficulty of color extraction), is the highest among all the plants investigated here. Indeed, T. populnea is characterized by the reddish bloody color of its bark extract (with the highest red a*-value of + 55.1 in the CIELab system among all the color extracts analyzed) with a promising extraction yield of 12.8 kg per 100 kg of barks (dry matter; dm.) obtained after a solid/liquid eco-extraction using ethanol and water mixture (70:30, v/v), and a high pH and temperature stability of the extract containing reddish water-soluble dyes (Table 5).

Red color is one the most used color in the industries. Even if sources of reddish colors are already available in the market like carminic acid from Dactylopius coccus or bixin from Bixa orellana, the research of other natural sources are still in demand because the actual colorants in the market don't really offer the bright red color that their artificial counterparts offer. Thus, our results demonstrated that barks of T. populnea, as well as the dyestuff extracted from barks of Weinmannia tinctoria (a*-value of + 47.8; yield of 16.9 kg per 100 kg dm.; dye score of 56), barks of Leea guinensis (a*-value of + 42.4; yield of 16.8 kg per 100 kg dm.; dye score of 50), barks of Pemphis acidula (a*-value of + 30.7; yield of 11.6 kg per 100 kg dm.; dye score of 49), barks of Erythroxylum laurifolium (a*-value of + 48.7; yield of 6.1 kg per 100 kg dm.; dye score of 48). Roots of Morinda citrifolia (orangish-red color; a*-value of + 35.5; yield of 13.8 kg per 100 kg dm.; dye score of 44) offered promising color extracts containing water-soluble dyes which give a bright red or orangish-red coloration at low concentrations (from 2 to 8 mg/mL) (Table 5). The wavelength of maximum absorbance obtained around 500 and 550 nm in visible confirms the reddish color given by these selected plant-based dyestuffs. These red colors may come from different chemical classes of natural dyes like tannins, proanthocyanidins, flavonoids, alkaloids, anthraquinones, etc. (Tables 2,3). Furthermore, the reddish colors of T. populnea, W. tinctoria, L. guinensis, P. acidula, E. laurifolium and M. citrifolia extracts can be considered as highly stable considering that they are able to support a wide range of pH (from 4 to 10 in water buffer solutions) and temperature (from 25 to 95 °C) with no significant variation; only an instability (discoloration) to acidic pH was observed for the extract of M. citrifolia roots.

Natural source of orangish and yellowish colorants are the second most used colorants in the dye industries. With red and blue, yellow is classified as one of the primary colors. Even if many sources of yellow colors are proposed in the market like curcumin or carotenoids (lutein…), the main limits of these colorants are their low stability. Our results indicated that many dye plant species from Reunion Island contain orangish and yellowish dyes. These colored molecules can be alkaloids, flavonoids, quinonoids, etc. 5). Stability characterization performed on these color extracts demonstrates a high stability toward temperature and pH of O. borbonica and T. bentzoe extracts, and a high stability specially toward temperature for D. fragrans extract; interestingly, this last extract turns red in alkaline pH (Table 5). Compared to commercial Reseda luteola extract, a common dye plants used in European country as a yellow colorant, the color stability of these above interesting sources of yellowish-orange colorants from Reunion Island is very promising for dyeing applications. This current study offered a real choice of new natural sources of yellowish-orange dyes that remain stables. Then, greenish-brown, orangish-brown, yellowishbrown, beige, or pale beige-orange colors were obtained by the others endemic and native species harvested in this study (Table 5). For instance, the leaves of Pandanus utilis (yield of 12.7 kg per 100 kg dm.; dye score of 44) produce a pale greenish extract at low concentration, but give a bright greenish-dark color at a concentration of 8 mg/ml. The color remains greenish a few days later both in acidic and alkaline medium. This property is very uncommon for pigments extracted from green leaves and it will be of interest to analyze the chemical classes of the pigments extracted. The leaves of Talipariti tiliaceum (yield of 13.5 kg per 100 kg dm.; dye score of 34) also give a greenish-dark color extract of interest for dyeing application. Interestingly this greenish-brown color turns red in alkaline pH, and the same applies to leaves of the species Pteridium aquilinum which give an intense red in alkaline pH. Furthermore, from a mixture of barks and stems of the native species T. tiliaceum, an original pinkish-buff shade was obtained. Finally, a selection of 15 introduced cultivated or alieninvasive species in Reunion Island, among the 138 alien species inventoried below (Table 3 and Additional file 1: Table S1), have also been harvested and characterized in this part of the study. Main results in terms of extraction yield and coloring properties (shade, solubility and stability) for these introduced species are summarized in Table 6. Water-soluble dyes with various shades were obtained according to the dye plants, like pink-violet from fruits of Selenicereus undatus (cultivated), yellowish-orange shade for rhizomes of Curcuma longa (cultivated), leaves of Terminalia catappa (cultivated), stems of Antigonum leptopus (invasive), barks of Casuarina equisetifolia (invasive) or fruits of Coccoloba uvifera (cultivated), and greenish shade for leaves of Leucena leucocephala (invasive). The Reunion's forest is a remarkable reserve of plant biodiversity, and the most promising dye plant species (endemic, native, alien cultivated or invasive) may be used in dyeing application for the industries subject to their successful application for coloring textiles, food or cosmetics.

Bath-dyeing applications on natural fibers of dye plants from Reunion Island

Textile industry is a huge industry and this is crucial to change the way textiles are designed to an eco-friendlier production by using natural textile dyes [START_REF] Fazal-Ur-Rehman | Environmentally friendly bio-dyeing of silk using Alkanna tinctoria based Alkannin natural dye[END_REF]. Proven toxicity and environmental burdens caused by artificial azo dyes and related hazardous substances applied for textile dyeing, especially in Asia-Pacific region (China and India), have motivated consumers and industrials to turn to natural and eco-friendly fabric dyeing alternatives [START_REF] Adeel | Ecofriendly application of coconut coir (Cocos nucifera) extract for silk dyeing[END_REF]. In this study, for the first time to our knowledge, the most promising plant-based dyestuffs from Reunion island rich in water-soluble dyes have been investigated for textile dyeing application on natural fibers (wool and cotton). For cotton dyeing, it is usually necessary to perform a mordanting step to improve the dye strength fixation on the fabrics. Choice of mordant is important insofar each complex mordant-textile may give a specific color and light. Thus, the dyeing property of the plant extracts has been checked for bath-dyeing with different mordants (alum, aluminum acetate, tannins, and ferrous sulphate, either alone or in combination). Main results and shades obtained after the bath-dyeing process using the reddish color extracts from T. populnea, W. tinctoria, E. laurifolium, M. citrifolia, and L. guinensis are presented in Fig. 2. Similarly, results obtained after the bath-dyeing process utilizing the yellowish-orange color extracts from O. borbonica, D. fragrans, T. bentzoe, T. cattapa, and C. equisetifolia are described in Fig. 3. These experiments have demonstrated very successful and very positive results. By using the adequate dye plant and mordant, it is possible to color the fabrics in a variety of different colors, like bright red with M. citrifolia extract, reddish with W. tinctoria, terracotta and pinkish-orange color with T. populnea and E. laurifolium (turn dark-green with iron mordant), sandy (pale yellow, cream) color with L. guinensis, bright yellowish-khaki color with O. borbonica (turn orangish pink with tannins added, and into dark-green with tannins and iron mordant), ochre-yellow and vibrant auburn colors with D. fragrans (turn ochrered color in alkaline pH), yellow/beige color with T. bentzoe and T. cattapa (turn dark-blue or black with iron mordant), sandy color with C. equisetifolia (turn deepblue with iron mordant, and into terracotta in alkaline pH), yellow and pinkish color with Coccoloba uvifera, etc.

Conclusion

Reunion Island has a multitude of plant species that have potential as a source of new compounds or new raw materials for the dye industries. The current study demonstrated that even if the local sector of natural dyes and uses of plants as source of colorants and pigments are recent to the Island, the biodiversity of Reunion Island has the potential to offer a large choice of alternative sources of colorants and pigments for industry.

After literature review and surveys made on local population, an original classification method has been established to rank the different dye plants collected using different criteria like endemicity, parts used and colors. As a preliminary study, this first survey and classification will direct researchers and industrials to a smaller sample of plants to investigate as the next sources of natural colorants and pigments. It embraces biodiversity and the importance of recovering species that are endemic and/ or native to Reunion Island biodiversity which could be used as natural colors. This study also illuminates additional research to be carried out where there is a lack of scientific knowledge and great potential for socio-economic impact through natural colorants from plants origin growing in tropical or sub-tropical regions.

The Indian Ocean region still offers huge potential for discovering new sources of plant-based dyestuffs. The current study is only a first step to demonstrating that the recovery of natural dyes from these tropical regions has a bright future for researchers, industry and consumers. Thus, there is no doubt this is the tip of the iceberg, and many other tropical plant species should be investigated to unveil myriad of other useful natural compounds.

( 1 ) 8 Fig. 1 .

 181 Fig. 1. The collection of plant species growing in protected areas or territories of the national park has been validated by the competent authorities under the authorization N° DIR/SEP/2021/144 and DIR-I-2021-335. Identification and conservation of each species harvested have been made by botanists of the CBNM. Voucher specimens have been deposited in the herbarium of the CBNM.The CBNM collection form was used for the traceability of each collection. Depending on the species, adventitious roots, barks, stems, leaves, flowers, fruits or lianas were collected. The harvesting was done according to good practices in order to reduce adverse effect on the plants. For example, in the case of bark and roots, a part was scraped off and then pine tar was sprayed on the cut to avoid external contamination. The quantity of fresh material to be collected varies according to the part of the plant concerned. Thus, the ideal proportions to be collected to ensure a sufficient quantity of fresh material for pigment extraction were estimated at 500 g for barks and roots, 1 000 g for leaves and flowers, and 2 000 g for fruits. Plant organs were collected from three different trees or shrubs from the same geographical and geological area, and they were then mixed to constitute one representative collection batch. The collection was repeated three times.Each collection batch undergoes various pre-treatments before pigment extraction, including cutting, drying and grinding. All samples were firstly cut into small

Fig. 1

 1 Fig. 1 Map of Reunion island, with some plant collection points (1: Ravine des Colimaçons, 2: Notre Dame de la paix forest, 3: Mare Longue forest, 4: Piton Partage, 5: Tremblet, 6: National Botanical Conservatory of the Mascarene, 7: Cilaos, 8: Étang-Salé) (Source: Google map)

  Three plant-based dyestuffs, namely barks and stems of Ochrosia borbonica (b*-value of + 94.7; yield of 15.5 kg per 100 kg dm.; dye score of 46), roots of Danais fragrans (b*-value of + 93.4; yield of 15.1 kg per 100 kg dm.; dye score of 44), and barks of Terminalia bentzoe (b*-value of + 67.4; yield of 31.4 kg per 100 kg dm.; dye score of 40) give a bright yellowishorange color (yellow at low concentration and orange in concentration of 8 mg/ml or greater) (Table

Fig. 2

 2 Fig.2Natural wool and cotton dyeing by bath-dyeing process utilizing the reddish color extracts from T. populnea, W. tinctoria, E. laurifolium, M. citrifolia, and L. guinensis. Six different mordants were added in the dye-bath[START_REF] Adeel | Sustainable application of microwave assisted extracted tea based tannin natural dye for chemical and bio-mordanted wool fabric[END_REF][START_REF] Adeel | Ecofriendly application of coconut coir (Cocos nucifera) extract for silk dyeing[END_REF][START_REF] Hussaan | Microwaveassisted sustainable exploration of cocklebur leaves (Xanthium strumarium L.) as a novel source of distinct yellow natural colorant for dyeing cotton fabric[END_REF][START_REF] Batool | Sustainable natural coloring potential of bitter gourd (Momordica charantia L.) residues for cotton dyeing: innovative approach towards textile industry[END_REF][START_REF] Deuil | Etude de positionnement de la production et de l'usage de pigments et colorants naturels à partir de ressources d'origine végétales de l'Ile de la Réunion[END_REF][START_REF] Andriamanantena | Malagasy Dye Plant Species: A Promising Source of Novel Natural Colorants with Potential Applications -A Review[END_REF]

Fig. 3

 3 Fig. 3 Natural wool and cotton dyeing by bath-dyeing process utilizing the yellowish-orange color extracts from O. borbonica, D. fragrans, T. bentzoe, T. cattapa, and C. equisetifolia. Six different mordants were added in the dye-bath (1-6)

  1/Do you know any dye plants, i.e., plants that are sources of pigments or dyes? 2/Are you familiar with natural dyeing? Yes/No 3/If yes, which ones do you know? 4/According to you, which ones have been traditionally used in Reunion Island? 5/According to you, what are the parts of the plant used for each species? 6/In your opinion, what are the collection methods and have these plants been cultivated? 7/According to you, what are the extraction methods and preparations that were or are currently used for dyeing? 8/What are the different applications where dyeing from plants has been used: tanning, dyeing, medicinal use, food, crafts? 9/Was there a trade of the extracted substances and if so, according to which economic model? 10/Do you know any references or literature sources or people describing dye plants?. "

Table 1

 1 Notation of the 8 criteria for scoring the "dye score" of the plant species from La Réunion Island biodiversity

	Criterium

Description Notation of the criterium on a scale of 1 to 10 1 3 7 10

	Strict endemic of Reunion Island							No article in the studied species					Abundant species in cultivation	and easy access: both in cultiva-	tion (CBNM arboretum) and	in the wild (EEE), no resupply	problem		Cultivable and currently culti-	vated in La Réunion				Leaves													Multiples known uses > 5
	Regional endemic (Mas-	carenes)						Some references in literature	but pigments not known				Abundant species in the wild	with relatively easy access (no	resupply problems)				Potentially cultivable from its	reproduction mode				Stems, barks, fruits, flowers													3-4 other known uses
	Native or cryptogenic							Species relatively well	described in the literature				Species accessible with permis-	sion: private land, departmen-	tal-domain, national park, but	with enough plants available	for collection		Cultivable but very slow grow-	ing (e.g., 10-year-old tree)				Adventitious roots													1-2 other known uses
	Introduced (alien)							Species perfectly described in	literature and pigments identi-	fied (known structure)			Protected and rare species	(with difficult access)					Not cultivable					Wood, all plant													No other known uses apart	from traditional dyeing
	Valued endemic plants	because of their potential as a	locally available resource that	can lead to regional economic	development in addition to the	extension and conservation of	biodiversity	Valued the identification	of species not previously	described in the scientific	literature, nor enhanced in the	industrial field	Valued locally available plants	that have a high economic	potential for the territory. It is	essential to prioritize readily	accessible species that are not	protected in Reunion	Valued cultivability to elevate	species already cultivated on	the island and plants whose	reproduction and cultivation	methods are known	Valued sustainability by	prioritizing use of the most	renewable parts of the plant.	Leaves can be harvested	throughout the year, bark can	be collected if it does not affect	the future development of the	plant. Flowers and fruits are	seasonal but if the yield is high,	these parts have potential. The	collection of the woody part	of a plant can kill it and are	therefore not sustainable	Valued other medicinal, biogas,	nutritional or other uses	beyond the coloring properties	of the plant-greater eco-	nomic interest
	C1-Indigenous status of spe-	cies on La Réunion Island						C2-Scientific knowledge	about species				C3-Accessibility and avail-	ability of species on La Réunion	Island				C4-Cultivability of plant	species				C5 -Plant organs used for pig-	ment extraction												C6-Industrial interests and	other known applications of	plant species

Table 1 (continued) Criterium Description Notation of the criterium on a scale of 1 to 10 1 3 7 10

 1

	Rare/special and relatively stable	color (blue, magenta, pink, cyan,	mauve, black…)							Pigments extractable with EtOH	aqueous in good yield
	Desired color (red, orange, yel-	low…) and relatively stable								Pigments extractable with	EtOH aqueous in average yield
	Unattractive (beige, brown,	etc.) and/or unstable color								Pigments extractable only with	non-eco-compatible solvents	(e.g., hexane)
	Colorless or very light-colored	extract								Mordanting or fermentation	useful for color expression
	Valued rare/special colors (blue,	magenta, pink, cyan, mauve,	black…). Yellow, orange and	red are sought in the dyeing	industries to replace synthetic	dyes, but only if they have	an intense and stable color.	Brown and beige colors are less	demand	Valued plants containing	water-soluble pigments and	dyes that are easily extract-	able using water and ethanol	(eco-compatible solvents) with	adequate yield for industrial	applications, and whose color	can be realized without mor-	danting or fermentation
	C7-Color and stability of dyes	and pigments extracted from	plant species							C8-Yield and difficulty of	color extraction

Table 2

 2 Endemic plant species in La Réunion Island potentially rich in dyes or pigments

	Cited references					[38]					[21]				[21]				[39, 40]					-		[18, 28, 41]					-			-				-
	Main	components				Anthraquinones,	flavonoids				Alkaloids, flavo-	noids, saponosids,	tannins, leucoan-	thocyans	Alcaloids, flavo-	noids, saponosids,	tannins, leucoan-	thocyans	Proanthocya-	nidins, condensed	tannins, flavonoids	(quercitrin and	afzelin)	n.d		Tannins					n.d			n.d				n.d
	Plant organs Color produced Known	traditional uses	and applications,	and cultural	status	Leaves Dark yellow; green Ornamental,	medicinal uses;	cultivated for	conservation	purposes	Fruits Bluish, brown Medicinal uses;	cultivated occa-	sionally		Fruits Bluish, brown Medicinal uses;	cultivated occa-	sionally		Bark, stems Red Medicinal uses,;	cultivated occa-	sionally			Wood Red Cultivated occa-	sionally	Wood Red-brown Ornamental;	cultivated for	ornament and	conservation	purposes	Stems n.d Ornamental;	uncontrolled	culture	Flower Yellow-green Medicinal uses,	ornamental;	cultivated for eco-	nomic purposes	Flower Bright yellow Medicinal uses,	ornamental;	cultivated for eco-	nomic purposes
	Endemicity level IUCN Red List	Categories &	Protection status	(French law)*		Endemic Réunion EN/Protected					Endemic Réunion DD				Endemic Réunion LC				Endemic Réunion-LC	Mauritius				Endemic Réunion-LC	Mauritius	Endemic Réunion-CR/Protected	Mauritius				Endemic Réunion LC			Endemic Réunion LC				Endemic Réunion-LC	Comoros
	Species Family Local vernacular	name				Aloe macra Haw ASPHODELACEAE Mazambron	marron				Bertiera borbonica RUBIACEAE Bois de raisin	A. Rich. ex DC			Bertiera rufa DC RUBIACEAE Bois de raisin				Erythroxylum ERYTHROXY-Bois de rongue	laurifolium Lam LACEAE				Ficus densifolia Miq MORACEAE Affouche		Foetidia mauritiana LECYTHIDACEAE Bois puant	Lam				Forgesia racemosa ESCALLONIACEAE Bois de Laurent-	J.F. Gmel Martin		Hubertia ambavilla ASTERACEAE Ambaville	Bory var. ambavilla			Hypericum lanceo-HYPERICACEAE Fleur jaune	latum Lam

Table 2 (

 2 continued)

	Cited references					[16, 18, 27]					-				-			[21, 26]			-		[34-37]				[42]			[43, 44]			[43, 44]			[43, 44]			[22]
	Main	components				Tannins					Alkaloids				Tannins			n.d			Tannins		Alkaloids				n.d			Flavonoids			Flavonoids			Flavonoids			Alcaloids, flavo-	noids, saponosids,	tannins, leucoan-	thocyans
	Plant organs Color produced Known	traditional uses	and applications,	and cultural	status	Wood Red Ornamental, wood	stain; cultivated	for ornament	and conservation	purposes	Leaves Black Ornamental;	cultivated for	ornament and	landscaping	Bark Brown Ornamental; culti-	vated for forestry	purposes	Bark, stems Brown Medicinal uses;	cultivated occa-	sionally	Bark n.d -; uncontrolled	culture	Bark Yellow Medicinal uses;	cultivated for	conservation	purposes	Bark Red, orangish Medicinal uses;;	cultivated occa-	sionally	Whole plant Greenish-brown Medicinal uses;	uncontrolled	culture	Whole plant Greenish-brown Medicinal uses;	uncontrolled	culture	Whole plant Greenish-brown Medicinal uses;	cultivated occa-	sionally	Stems, leaves n.d Medicinal uses;	uncontrolled	culture
	Endemicity level IUCN Red List	Categories &	Protection status	(French law)*		Endemic Réunion CR/Protected					Endemic Réunion CR/Protected				Endemic Réunion-LC	Mauritius		Endemic Réunion-LC	Mauritius		Endemic Réunion-LC	Mauritius	Endemic Réunion-VU/Protected	Mauritius			Endemic Réunion-VU	Mauritius		Endemic Réunion LC			Endemic Réunion LC			Endemic Réunion LC			Endemic Réunion-LC	Mauritius
	Local vernacular	name				Bois de sable					Latanier rouge				Grand natte			Tan Georges			Mapou à petites	feuilles	Bois jaune				Corce rouge, bois	d'effort		Bouillon blanc			-			Ti mangue			Bois cassant
	Family					FABACEAE					ARECACEAE				SAPOTACEAE			SAPINDACEAE			MONIMIACEAE		APOCYNACEAE				OLACACEAE			ASTERACEAE			ASTERACEAE			ASTERACEAE			RUBIACEAE
	Species					Indigofera	ammoxylum (DC.)	Polhill			Latania lontaroides	(Gaertn.) H.E.	Moore		Mimusops balata	(Aubl.) C.F. Gaertn		Molinaea alternifo-	lia Wild		Monimia ovalifolia	Thouars	Ochrosia borbonica	J.F. Gmel			Olax psittacorum	(Lam.) Vahl		Psiadia anchusifolia	(Poir.) Cordem		Psiadia calloceph-	ala (Bory) Cordem		Psiadia dentata	(Cass.) DC		Psychotria bor-	bonica (J.F. Gmel.)	Razafim. B.Bremer

Table 2

 2 (continued)

	Cited references					-					[45, 46]				[18, 26, 30, 32, 47]					-		[17, 29, 30]
	Main	components				n.d					Flavonoids				Tannins					Tannins		Tannins
	Plant organs Color produced Known	traditional uses	and applications,	and cultural	status	Bark n.d Ornamental;	cultivated for	ornament and	conservation	purposes	Bark, leaves n.d Softwood lumber;	medicinal uses;	cultivated occa-	sionally	Bark Yellow, black Medicinal uses,	ornamental;	cultivated for	ornament and	landscaping	Bark n.d Uncontrolled	culture	Bark Red Leather dye-	ing (not today);	cultivated today	to support honey	production in	Reunion Island;	cultivated for	ornament and	landscaping
	Endemicity level IUCN Red List	Categories &	Protection status	(French law)*		Endemic Réunion CR/Protected					Endemic Réunion EN/Protected				Endemic Réunion-CR/Protected	Mauritius				Endemic Réunion-LC	Mauritius	Endemic Réunion-LC	Mauritius
	Local vernacular	name				Bois de senteur	blanc				Petit tamarin des	Hauts			Benjoin					Petit bois de tan		Tan rouge
	Species Family					Ruizia cordata Cav MALVACEAE					Sophora denudata FABACEAE	Bory			Terminalia bentzoe COMBRETACEAE	(L.) L.f. subsp.	bentzoe			Weinmannia mau-CUNONIACEAE	ritiana D. Don	Weinmannia CUNONIACEAE	tinctoria Sm

NE Not Evaluated, DD Data Deficient, LC Least Concern, NT Near Threatened, VU Vulnerable, EN Endangered, CR Critically Endangered, EW Extinct in the Wild and EX, n.d. not determined *IUCN Red List Categories

Table 3

 3 Native and cryptogenic plant species in La Réunion Island potentially rich in dyes or pigments

	Cited references					-			[57]			-		[21, 58-60]				[6, 24]					[6, 61, 62]		[22, 63]				[9, 29]				[64, 65]			-	[59]
	Main	components				n.d			n.d			n.d		alcaloids, flavo-	noids, phenols,	triterpens,	tetrapyrrols	Flavonoids, tan-	nins, Mangiferine				Alkaloids, flavo-	noids	Alcaloïds	(pyrrolizidine,	monocrotaline,	retrorsine)	Quinonoid				Anthocyanins			n. d	n. d
	Plant organs Color produced Known	traditional uses	and applications,	and cultural	status	n.d n.d Ornamental; culti-	vated occasionally		Fowers, roots Yellow Medicinal uses;	uncultivated		n.d n.d Ornamental; culti-	vated occasionally	Leaves, bark Greenish Medicinal uses;	cultivated occa-	sionally		Leaves, stem, bark Yellow Medicinal uses;	cultivated occa-	sionally			Liana Orangish, yellow Medicinal uses;	uncultivated	n.d n.d Toxic plants;	uncultivated			Roots Orangish-red Ornamental,	medicinal uses;	cultivated occa-	sionally	Fruits Blue Medicinal uses;	cultivated for	ornament	Leaves, bark Yellow, dark Ornamental,	medicinal uses;	cultivated for	ornament and	landscaping	Leaves n.d Ornamental; culti-	vated occasionally
	Endemicity level IUCN Red List	Categories &	Protection status	(French law)*		Native (Africa, LC	Madag., Réunion,	Mauritius);	Native (E. Africa, LC	Madag. to S. China	and Philippines)	Native (Madag., LC	Comoros);	Native (Madagas-LC	car, Mauritius);			Native (SE trop. LC	Africa, Madag.,	Comoros,	Mascarenes,	Seychelles);	Native (Pantropi-LC	cal); invasive	Cryptogenic NA	(Pantropical)			Native (Mauritius, LC	Madag.);			Cryptogenic DD	(Madag., Sey-	chelles, Asia);	Native (Pantropi-LC	cal);	Native (Madag., LC	Mascarenes)
	Species Family Local vernacular	name				Agarista salicifolia ERICACEAE Bois de rempart	(Comm. ex Lam.)	G. Don	Alectra sessiliflora OLEACEAE -	(Vahl) Kuntze		Antidesma mada-PHYLLAN-Bois de cabri	gascariense Lam THACEAE blanc	Antirhea bor-RUBIACEAE Bois d'osto	bonica J.F. Gmel			Aphloia theiformis APHLOIACEAE Change-écorce	(Vahl) Benn				Cassytha filiformis LAURACEAE Liane foutafout	L	Crotalaria retusa L FABACEAE Pois rond marron,	crotalaire			Danais fragrans RUBIACEAE Liane jaune	(Lam.) Pers			Dianella ensifolia ASPHODELACEAE Vacoa nain, reine	(L.) DC des bois		Dodonaea viscosa SAPINDACEAE Bois d'arnette	Jacq	Doratoxylon SAPINDACEAE Bois de gaulette	apetalum (poir.)	Radlk

Table 3

 3 (continued)

	Cited references					-			[6]					[48-50]				[6, 66]			-				[56]					-				[25]			[67]		[46]
	Main	components				n. d			Flavonoids, tan-	nins, terpenes				Polyphenol, flavo-	noid, quinonoid			n. d			n. d				n. d					n. d				Saponines			Flavonoids, tan-	nins, alkaloids	n. d
	Color produced Known	traditional uses	and applications,	and cultural	status	Red Ornamental;	uncultivated		Red Ornament,	medicinal uses;	cultivated for	ornament and	landscaping	Orange, Yellow Food and	medicinal uses;	cultivated occa-	sionally	Orangish-red Medicinal uses;	cultivated occa-	sionally	n.d Ornamental;	cultivated for	ornament and	landscaping	Yellow, green Ornamental, food	uses; Cultivated	for economic	purposes and for	landscaping	Red Ornamental;	cultivated for	conservation	purposes	Greenish Medicinal uses;	cultivated occa-	sionally	Black , medicinal uses;	uncultivated	Reddish Ornamental,	medicinal uses;	cultivated for	ornament and	landscaping
	Plant organs					Wood			Barks					Roots				Roots, flowers			Leaves				Terminal buds,	leaves				Barks				Leaves			Leaves, fruits		Bark, sap
	Species Family Local vernacular Endemicity level IUCN Red List	name Categories &	Protection status	(French law)*		Ficus rubra Vahl MORACEAE Affouche rouge Native (Madag., LC	Comoros, Seych.,	Mascarenes);	Leea guineensis VITACEAE Bois de sureau Native (Trop. LC	G. Don Africa, Madag.,	Mauritius)			Morinda citrifolia L RUBIACEAE Malaye, noni Native (Indopa-DD	cific)			Mussaenda RUBIACEAE Lingue café Native (Mas-LC	arcuata Poir carenes, Madag.,	Africa);	Olea lancea Lam OLEACEAE Bois d'olive blanc Native (Madag., LC	Mascarenes)			Pandanus utilis PANDANACEAE Vacoa Native (Mas-LC	Bory carenes)				Pemphis acidula LYTHRACEAE Bois matelot Native (Paleotropi-LC	J.R. Forst. et G. cal);	Forst		Phymatosorus POLYPODIACEAE Patte-lézard Native (Africa, LC	scolopendria trop. Asia to Austr.	(Brum f.) Pic Serm and Polynesia);	Pteridium aquili-DENNSTAEDTI-Fougère aigle Native (Cosmop.); LC	num (L.) Kuhn ACEAE invasive	Securinega duris-PHYLLAN-Bois dur Native (Mascar., LC	sima J.F. Gmel THACEAE Madag., Mayotte);

Table 3

 3 (continued) NE Not Evaluated, DD Data Deficient, LC Least Concern, NT Near Threatened, VU Vulnerable, EN Endangered, CR Critically Endangered, EW Extinct in the Wild and EX, n.d. not determined *IUCN Red List Categories

	Cited references					-					[6, 51, 52, 54, 68]
	Main	components				Quinones, lapa-	chol				Polyphenols,	flavonoids, tan-	nins, terpenes,	alkaloids
	Color produced Known	traditional uses	and applications,	and cultural	status	n.d Ornamental,	medicinal uses;	cultivated for	ornament and	landscaping	Red to light Medicinal uses;	brown cultivated for	ornament and	landscaping
	Plant organs					Bark, leaves					Fruits, flowers,	bark
	Endemicity level IUCN Red List	Categories &	Protection status	(French law)*		Native (Trop. and EN/Protected	subtrop. regional	coast) cultivated			Cryptogenic DD	(Coastal pantropi-	cal) cultivated
	Local vernacular	name				Mova, var					Porché
	Family					MALVACEAE					MALVACEAE
	Species					Talipariti tiliaceum	(L.) Fryxell				Thespesia pop-	ulnea (L.) Sol. Ex	Corrêa

Table 4

 4 Examples of alien cultivated and invasive plant species in La Reunion Island potentially rich in dyes or pigments

	Cited references					[80, 81]			[81, 82]			[79]			[76, 77]					[83]			[84]			/					[85, 86]		[87]			/		[88]	/
	Color produced Known Main	traditional uses components	and applications,	and cultural	status	Black Medicinal uses; Flavonoid, alka-	restoration; horti-loid, tannins	culture	Yellow, pink, grey, Medicinal uses; Tannins, proan-	brown, black horticulture; thocyanidin	firewood	Brown, green Medicinal uses; Phenolic com-	ornament pounds, tannins,	anthraquinons	Pink, brown Dyeing; firewood; Casuarine	against beach	erosion			Red Medicinal uses; D-Borneol	dietary		Purpleish Ornament; medic-Anthocyanins,	inal uses; dietary; anthocyanidins,	woodworking	Copper apricot, Medicinal uses; Terpinene,	flesh color essential oil; insec-p-cymene,	ticide; woodwork-3-carene,	ing terpinolene, beta-	myrcene	Dark yellow Medicinal uses; Polyphenols,	dietary curcumins	n.d Medicinal uses; Tannins	fodder; firewood		Yellow Ornament; textile n.d		Reddish Medicinal uses; Anthocyanins,	uncontrolled Phenolics, carot-	culture; dietary; enoids	woodworking	Turquoise Ornament n.d
	Plant organs					Bark, pods,	flowers		Bark, pods			Leaves, stems and	flowers		Bark, leaves					Leaves			Fruit, leaves			Leaves					Rhizome		Leaves			Whole plant		Wood, fruit	Fruit
	IUCN Red List	Categories	& Protection	status (French	law)	NA			NA			NA			NA					NA			NA			NA					NA		NA			NA		NA	NA
	General status	(region of origin)				Alien invasive	(Australia, Tas-	mania)	Alien invasive	(Australia)		Alien invasive	(Mexico and Cen-	tral America)	Alien cultivated,	invasive (Indopa-	cific litt., Australia	and New-Cale-	donia)	Alien cultivated,	invasive (South-	East Asia)	Alien cultivated	(Atlantic Ameri-	can littoral)	Alien cultivated	(Japan)				Alien cultivated	(India)	Alien invasive	(Central America)		Alien cultivated	(New Zealand)	Alien cultivated	and invasive	(Brazil)	Alien cultivated,	naturalized	(Madagascar)
	Family Local vernacular	name				FABACEAE Acacia Bernier,	mimosa		FABACEAE Acacia			POLYGONACEAE Liane antigone			CASUARINACEAE Filao					LAURACEAE Ti cannelle			POLYGONACEAE Raisin de mer			CUPRESSACEAE Cryptoméria					ZINGIBERACEAE Safran-pays		FABACEAE Cassi			ASPHODELACEAE Vacoa de laine		MYRTACEAE Goyavier	STELITZIACEAE Ravenale, arbre du	voyageur
						Acacia dealbata	Link		Acacia mearnsii	De Wild		Antigonon lepto-	pus Hook. et Arn		Casuarina equiseti-	folia L				Cinnamomum	burmannii (Nees	et T. Nees) Blume	Coccoloba uvifera	(L.) L		Cryptomeria	japonica (L. f.) D.	Don			Curcuma longa L		Leucaena leuco-	cephala (Lam.)	de Wit	Phormium tenax	J.R. Forst. et G.	Forst	Psidium cattleya-	num Sabine	Ravenala mada-	gascariensis Sonn

Table 4 (

 4 continued)

	Cited references					[71]			[89]			[6, 73, 74]				[9]
	Main	components				n.d			Tannins			Tannins				n.d
	Color produced Known	traditional uses	and applications,	and cultural	status	Red, purple Medicinal uses;	dietary; defensive	hedges	Purple, yellowish Medicinal uses;	uncontrolled	culture; dietary	Brownish Medicinal uses;	dietary; ornament	(shady); firewood;	woodworking	Pale yellow Defensive	hedges;fodder
	Plant organs					Fruit			Fruit			Leaves, bark				Flowers
	IUCN Red List	Categories	& Protection	status (French	law)	NA			NA			NA				NA
	General status	(region of origin)				Alien cultivated,	invasive (Tropical	America)	Alien invasive,	cultivated (Indo-	Malaisia)	Alien (crypto-	genic?) cultivated	(Indopacific litt.)		Alien invasive	(Europe)
	Family Local vernacular	name				CAC TAC EAE Pitahaya			MYRTACEAE Jamblon			COMBRETACEAE Badamier				FABACEAE Ajonc d'Europe,	zépinard des	Hauts, Genêt
						Selenicereus	undatus (Haw.)	D.R. Hunt	Syzygium cumini	(L.) Skeels		Terminalia catappa	L			Ulex europaeus L

Table 6

 6 Colors obtained from some alien cultivated or invasive dye plants in Reunion island (as ranked by their dye score)

	Scientific

name of species Collection area Parts used Extraction yield

		CIELab
	Colors obtained	coordinates of the colour extract
		(at 8 mg/ml)

(kg per 100 kg of dm.)

Dye or pigment? Stability (pH and temperature) Dye score (1-100)

	Selenicereus undatus (syn. Hylocereus undatus)	Etang-Salé	Fruits	56,3 ±4,3	L:50.4; a:75.1; b: -21.6 (pinkish)	Water -soluble dye	Low pH/T° stability (turn violet in alkaline pH)	58
	Casuarina equisetifolia	Tremblet	Barks	10.4 ±0.6	L:63.3; a:24.9; b:60.3 (orangish-red)	Water -soluble dye	High pH/T° stability	53
	Curcuma longa	Saint-Joseph	Rhizomes	8.7 ±2.4	L:60.2; a:42.4; b:102.8 (yellow to orange)	Water -soluble dye	High pH/T° stability (turn red in alkaline pH)	52
	Terminalia catappa	Saint-Pierre	Red leaves	20.7 ±0.4	L:65.0; a:15.5; b:88.2 (yellowish-orange)	Water -soluble dye	Stable to pH	46
	Acacia dealbata	Plaine des Sables	Barks	13.6 ±0.2	L:55.2; a:36.2; b:79.7 (orangish-red)	Water -soluble dye	High pH/T° stability	46
	Acacia dealbata	Plaine des Sables	Stems	7 .4 ±0.3	L:58.6; a:28.3; b:74.7 (orangish-brown)	Water -soluble dye	High pH/T° stability	46
	Coccoloba uvifera	Etang-Salé	Barks	12.7 ±1.8	L:67.4; a:23.8; b:66.5 (reddish)	Water -soluble dye	High pH/T° stability (red more intense in alkaline pH)	44
	Coccoloba uvifera	Etang-Salé	Fruits	13.1 ±1,5	L:79.6; a:8.6; b:40.1 (pinkish-orange)	Water -soluble dye	High pH/T° stability	44
	Coccoloba uvifera	Etang-Salé	Leaves	15.1 ±1.3	L:61.4; a:6.7; b:72.8 (yellowish-brown)	Water -soluble dye	High pH/T° stability	44
	Antigonum leptopus	Saint-Leu	S tems	16.2 ±0.4	L:58.9; a:20.1; b:62.6 (orangish-brown)	Water -soluble dye	High pH/T° stability	40
	Ficus carica	Cilaos	Barks	6 .9 ±0.4	L:80.6; a:-5.7; b:60.7 (greenish-brown)	Insoluble pigments	High pH/T° stability	39
	Cinammomum burmani i	Etang-Salé	Leaves	21.1 ±1.4	L:75.8; a:-0.9; b:67.7 (yellowish-brown)	Insoluble pigments	High pH/T° stability	38
	Leucena leucocephala	Terre Sainte	Leaves	24.4 ±0.7		Water -soluble dye	High pH/T° stability	36
	Syzygium cumini
		Plaine des
		Sables

L:61.5; a:-3.3; b:91.5 (greenish-yellow) Colimaçons Fruits 38.0 ±3.9 L:85.8; a:2.0; b:14.5 (pale beige) Insoluble pigments Stable to pH 34 Psidium cattleyanum Cilaos Fruits L:83.9; a:0.8; b:25.7 (pale beige) Insoluble pigments Stable to pH 33 Acacia mearnsii

Acknowledgements

The authors would like to express their gratitude to all people, local dyers and small cosmetics manufacturers who have participated in this screening of La Réunion Island dye plant species diversity, and Prof. Dominique Cardon for his helpful discussion about the project PLANTIN investigated here. We gratefully acknowledge Aurélia Wolff who provided technical supports for wool and cotton dyeing with the dye plants collected in this study. We are grateful to the Réunion National Park (Parc National de la Réunion) and the National Forestry Office (Office national des Forêts-ONF) who authorized the collection of all protected plant materials.

Funding

This work was financially supported by grants from Europe and Conseil Régional de La Réunion, Réunion island (France) (Project PLANTIN, Grant number: N° Synergie RE0022957/Agreement number: GUR-DTI/20200508-0022957/European Regional Development Fund).

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Supplementary Information

The online version contains supplementary material available at https:// doi. org/ 10. 1186/ s13002-023-00580-w.

Additional file 1. Table S1. List of 194 plant species potentially rich in dyes or pigments inventoried in Reunion Island

Author contributions YC and TP supervised the project and were in charge of overall direction and planning. MA, SP, MD and CL carried out the ethnobotanical studies, contributed to data collection and data analysis. CF, JF and MT helped to the ethnobotanical studies and species identifications. MA, CL, YC, SP drafted the manuscript and designed the figures and tables. MA and YC wrote the final version of the manuscript with input from all authors. All authors have made critical revisions and have approved the final version of the manuscript.

Declarations

Ethics approval and consent to participate Not applicable.

Consent for publication

Not applicable.

Competing interests

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