Yohan Pillon

Laure Barrabé

Sven Buerki

How many genera of vascular plants are endemic to New Caledonia? A critical review based on phylogenetic evidence

Keywords: adaptive radiation, biodiversity hotspots, biogeography, extinction, Pacific islands, relicts, ultramafic rocks

New Caledonian endemic genera

New Caledonia is a biodiversity hotspot located in the south-western Pacific, well known for its rich, unique and endangered flora. The island flora has a high level of endemism at the species level (75%), but also at the generic and family (three endemic) levels. We review here the taxonomic validity of the c. 100 endemic New Caledonian genera of vascular plants (13%) by using the monophyly criterion based on available phylogenetic data. As observed for other island floras, some of these genera were recovered nested in larger genera and are consequently likely to lose their rank. After a critical review, we concluded that the New Caledonian plant vascular flora contains between 62 and 91 endemic genera. This large variation in the number of endemic genera is mainly caused by a lack of DNA sequences (eight genera) and limited phylogenetic evidence. This work highlights gaps of knowledge that will have to be addressed to stabilize the taxonomy of the New Caledonian flora. Although this study shows that several genera are not monophyletic, New Caledonia still harbours more endemic genera than any other islands in the Pacific Ocean. Preliminary results indicate that the high level of endemism at higher taxonomic levels could be explained by an accumulation of relictual lineages, rather than adaptive radiations. Hypotheses explaining this phenomenon are provided in this study.

INTRODUCTION

New Caledonia is well known for its rich and unique flora and is the smallest biodiversity hotspot listed by [START_REF] Myers | Biodiversity hotspots for conservation priorities[END_REF]. This archipelago, located in the southwestern Pacific, has an unusual geological history and does not have a volcanic origin like most Pacific islands. New Caledonia detached from Australia during the late Cretaceous (c. 80 million years ago; [START_REF] Pelletier | Geology of the New Caledonia region and its implications for the study of the New Caledonian biodiversity[END_REF]. During its drift eastward, New Caledonia was submerged under deep water as suggested by sediments [START_REF] Cluzel | Upper Eocene unconformity and pre-obduction events in New Caledonia[END_REF][START_REF] Picard | L'archipel néo-calédonien, 300 millions d'années pour assembler les pièces d'un puzzle géologique[END_REF]. Geological evidence strongly supports the emergence of New Caledonia at the Eocene (c. 37 million years ago) when a portion of oceanic crust was deposited over the island [START_REF] Cluzel | Upper Eocene unconformity and pre-obduction events in New Caledonia[END_REF][START_REF] Pelletier | Geology of the New Caledonia region and its implications for the study of the New Caledonian biodiversity[END_REF]. Weathering subsequently produced the ultramafic substrates, which are home to a peculiar flora [START_REF] Virot | La végétation canaque[END_REF][START_REF] Jaffré | Etude écologique du peuplement végétal des sols dérivés de roches ultrabasiques en Nouvelle-Calédonie[END_REF][START_REF] Isnard | How did the ultramafic soils shape the flora of the New Caledonian hotspot?[END_REF].

Thus in spite of its continental origin, the submergence of New Caledonia implies that the island was entirely re-colonized by terrestrial life after its Eocene emergence and it therefore fits the 'Darwinian' island hypothesis [START_REF] Grandcolas | New Caledonia: a very old Darwinian island?[END_REF] comparable to most Pacific islands.

New Caledonia is not only unique because of its species diversity and rate of endemism, but also because of its unique diversity of gymnosperms and early diverging angiosperms [START_REF] Morat | The taxonomic reference base Florical and characteristics of the native vascular flora of New Caledonia[END_REF], many of which qualify as relicts [START_REF] Grandcolas | Relict species: a relict concept?[END_REF]. The island harbours three endemic families and 98 endemic genera of vascular plants, a number much greater than most other Pacific islands [START_REF] Morat | The taxonomic reference base Florical and characteristics of the native vascular flora of New Caledonia[END_REF].

Recent reviews have suggested that the number of endemic genera on islands may be overestimated for many reasons [START_REF] Pj | Evidence-based review of the taxonomic status of New Zealand's endemic seed plant genera[END_REF], but a common pattern is that an endemic genus may be nested in a more widespread genus [START_REF] Buerki | Spatio-temporal history of the endemic genera of Madagascar[END_REF][START_REF] Stuessy | Paraphyly and endemic genera of oceanic islands: implications for conservation[END_REF]. There is no clear universal definition of what a genus is; however, there are a number of criteria that can be applied to circumscribe them (see, e.g., Garnock-Jones, 2014, for a review), including monophyly, ease of recognition (morphologically), minimizing redundancy and time of divergence. Although some of these criteria cannot be applied objectively and the delimitation of a genus may be considered as arbitrary, they may actually be in many cases higher evolutionary significant units [START_REF] Barraclough | The evolutionary reality of species and higher taxa in plants: a survey of post-modern opinion and evidence[END_REF].

In this review, we aimed to evaluate the status of all of the endemic New Caledonian genera of vascular plants based on available phylogenetic evidence. We mostly investigated whether each genus fulfils the most objective criterion to define genera: monophyly. We do not discuss here morphological distinctiveness for each genus except in a few cases where phylogenetic evidence is ambiguous. This synthesis should allow a more objective comparison of the flora of New Caledonia with that of other Pacific islands, for which this work has already been done (e.g. New Zealand; [START_REF] Pj | Evidence-based review of the taxonomic status of New Zealand's endemic seed plant genera[END_REF]. Identifying the most distinctive endemic genera is also paramount for the conservation of phylogenetic diversity [START_REF] Mace | Preserving the tree of life[END_REF][START_REF] Buerki | Incorporating evolutionary history into conservation planning in biodiversity hotspots[END_REF]. It has long been accepted that the flora of New Caledonia is composed of ancient elements and the offspring of recent migrants (Virot, 1956: 373;Carlquist, 1965: 42), but their classification requires more scrutiny because supposedly ancient groups such as New Caledonian Araucaria Juss. may be more recent than previously thought [START_REF] Kranitz | Evolutionary diversification of New Caledonian Araucaria[END_REF]. Thus, we hoped to gain evidence on the prevailing patterns of endemism in New Caledonia: an ancient species repository or a hot-bed of recent radiation (sensu [START_REF] Verboom | Origin and diversification of the Greater Cape flora: ancient species repository, hot-bed of recent radiation, or both?[END_REF]. We also hope that this review will trigger further taxonomic work on the flora of New Caledonia by raising potential issues on generic delimitations and also encourage the inference of a generic level phylogeny for this unique flora.

REVIEWING THE PHYLOGENETIC STATUS OF THE NEW CALEDONIAN ENDEMIC

GENERA OF VASCULAR PLANTS Endemic genera are shown in bold on first appearance. We follow here a linear sequence based on APG [START_REF] Apg Iv | An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV[END_REF] and consider all the endemic genera listed in [START_REF] Morat | The taxonomic reference base Florical and characteristics of the native vascular flora of New Caledonia[END_REF] and the few others described or re-instated after that publication. For non-monotypic genera, we indicated in parenthesis the number of species (a) included in the cited phylogenetic studies and the total number of species per genus (b) as follows: genus (a/b). Numbers of species in endemic genera are taken from [START_REF] Munzinger | FLORICAL: checklist of the vascular indigeneous flora of New Caledonia vers[END_REF]. All of the endemic genera formed a monophyletic clade in the cited phylogenetic studies unless otherwise stated.

FERNS Gleicheniaceae

The monotypic Stromatopteris Mettenius is the only genus of fern endemic to New Caledonia. In molecular phylogenetic analyses including all genera of Gleicheniacae, Stromatopteris is recovered with strong support as sister to the Indo-Pacific Gleichenia Sm. [START_REF] Pryer | Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences[END_REF][START_REF] Lehtonen | Towards resolving the complete fern Tree of Life[END_REF].

GYMNOSPERMS

Podocarpaceae

The monotypic Parasitaxus de Laub. is the only known parasitic gymnosperm and is involved in an original type of parasitism with another podocarp [Falcatifolium taxoides (Brongn. & Gris) de Laub., also endemic to New Caledonia] that may also involve a fungus partner [START_REF] Feild | A unique mode of parasitism in the conifer coral tree Parasitaxus ustus (Podocarpaceae)[END_REF]. In a molecular phylogenetic analysis including all genera of Podocarpaceae, Parasitaxus forms a moderately supported clade with Manoao Molloy (New Zealand) and Lagarostrobos Quinn (Tasmania), both monotypic, although their exact relationships are unresolved. Parasitaxus may be sister to the other two taxa [START_REF] Sinclair | Evolutionary relationships of the New Caledonian heterotrophic conifer Parasitaxus ustus (Podocarpaceae), inferred from chloroplast trnL-F intron/spacer and nuclear ITS2 sequences[END_REF]. A close relationship between these three genera was confirmed by [START_REF] Lu | Phylogeny and divergence times of gymnosperms inferred from single-copy nuclear genes[END_REF], but their relationships are not resolved.

Cupressaceae

Phylogenetic data have demonstrated that the monotypic Neocallitropsis Florin is nested in the Australian and New Caledonian Callitris Vent. [START_REF] Pye | Divergence, diversity and species of the Australasian Callitris (Cupressaceae) and allied genera : evidence from ITS sequence data[END_REF]. This lineage is the sister group to the New Caledonian C. sulcata Schltr. (C. neocaledonica Dümmer was not included). Consequently, the sole species, N. pancheri (Carrière) de Laub., was recently transferred to Callitris [START_REF] Byng | The gymnosperms handbook: a practical guide to extant families and genera of the world[END_REF].

Taxaceae

The monotypic Austrotaxus Compton is the only representative of its family in the Southern Hemisphere. In a phylogenetic framework including all the genera of the family, [START_REF] Cheng | Phylogeny of Taxaceae and Cephalotaxaceae genera inferred from chloroplast matK gene and nuclear rDNA ITS region[END_REF] found that this genus was sister to the rest of tribe Taxeae (Taxus L., Pseudotaxus W.C.Cheng, from Eurasia, Malesia and North America) with strong support. This latter relationship was confirmed by [START_REF] Lu | Phylogeny and divergence times of gymnosperms inferred from single-copy nuclear genes[END_REF].

ANGIOSPERMS AMBORELLALES, Amborellaceae

Amborella Baill. (monotypic) is now usually accepted as the sister lineage to all angiosperms [START_REF] Qiu | The earliest angiosperms: evidence from mitochondrial, plastid and nuclear genomes[END_REF][START_REF] Soltis | Angiosperm phylogeny: 17 genes, 640 taxa[END_REF], although a few analyses have recovered Nymphaeales as its sister group (e.g. [START_REF] Goremykin | Analysis of the Amborella trichopoda chloroplast genome sequence suggests that Amborella is not a basal angiosperm[END_REF]. Amborella trichopoda Baill. is the first New Caledonian endemic plant to have had its genome entirely sequenced (Amborella Genome Project, 2013).

MAGNOLIIDS

LAURALES

Atherospermataceae

In a phylogenetic analysis including all genera of Atherospermataceae, the monotypic Nemuaron Baill. is recovered as sister to the Australian monotypic Atherosperma Labill. [START_REF] Renner | Timing transantarctic disjunction in the Atherospermataceae (Laurales): evidence from coding and non coding chloroplast sequences[END_REF].

Lauraceae

Adenodaphne S.Moore (1/4) has been recovered as the sister group to two species of Litsea Lam. from Japan and China with moderate support [START_REF] Chanderbali | Phylogeny and historical biogeography of Lauraceae: evidence from the chloroplast and nuclear genomes[END_REF]. Delimitation in Litsea (c. 400 species) and its allied genera requires clarifications (e.g. [START_REF] Fijridiyanto | Phylogeny of Litsea and related genera (Laureae-Lauraceae) based on analysis of rpb2 gene sequences[END_REF]. Since morphological confusions are possible between Adenodaphne and Litsea, also present in New Caledonia [START_REF] Kostermans | Flore de la Nouvelle-Calédonie et dépendances[END_REF], their distinctiveness needs to be critically assessed.

MONOCOTS LILIALES, Campynemataceae

Campynemataceae comprise only two genera, the Tasmanian monotypic Campynema Labill. and the New Caledonian Campynemanthe Baill. (1/3) that have been recovered as sister groups in phylogenetic analyses [START_REF] Vinnersten | Age and biogegraphy of major clades in Lilliales[END_REF][START_REF] Mennes | Ancient Gondwana break-up explains the distribution of the mycoheterotrophic family Corsiaceae (Liliales)[END_REF].

ASPARAGALES, Orchidaceae

The exact placement of some of the endemic genera (all terrestrial) is still somewhat uncertain, mostly because a number of related genera in this diverse family have not yet been included in any molecular phylogenetic analysis. This is particularly true for subtribe Goodyerinae [START_REF] Chase | An updated classification of Orchidaceae[END_REF]. Clematepistephium N.Hallé and Eriaxis Rchb.f. (both monotypic, tribe Vanilleae) are sister groups and together seem to be sister to the East Asian-New Guinean Lecanorchis Blume [START_REF] Cameron | On the value of nuclear and mitochondrial gene sequences for reconstructing the phylogeny of vanilloid orchids (Vanilloideae, Orchidaceae)[END_REF]. Pachyplectron Schltr. (1/3), has been recovered as sister to the rest of tribe Goodyerinae [START_REF] Alvarez-Molina | Molecular phylogenetics of Prescottiinae s.l. and their close allies (Orchidaceae, Cranichideae) inferred from plastid and nuclear ribosomal DNA sequences[END_REF]. Gonatostylis Schltr. (1/2) seems to be sister to Odontochilus Blume (synonym Pristiglottis Cretz. & J.J.Sm.; [START_REF] Alvarez-Molina | Molecular phylogenetics of Prescottiinae s.l. and their close allies (Orchidaceae, Cranichideae) inferred from plastid and nuclear ribosomal DNA sequences[END_REF], although the sampling of genera of Goodyerinae and Odontochilus spp. is limited in this study. The latter genus is found in Asia and the Pacific, including New Caledonia. Gonatostylis is also morphologically similar to the mycotrophic Danhatchia Garay & Christenson [START_REF] Ormerod | Danhatchia[END_REF] from New Zealand and Australia, which has never been included in any molecular phylogenetic studies. Achlydosa M.AClem. & D.L.Jones (monotypic) has been found to be sister to the Australasian Pterostylis R.Br. [START_REF] Cisternas | Phylogenetic analysis of Chloraeinae (Orchidaceae) based on plastid and nuclear DNA sequences[END_REF], the sole other member of subtribe Pterostylidinae [START_REF] Chase | An updated classification of Orchidaceae[END_REF], also present in New Caledonia. Coilochilus Schltr.

(monotypic) is sister to Cryptostylis R.Br. [START_REF] Kores | A phylogenetic analysis of Diurideae (Orchidaceae) based on plastid DNA sequence data[END_REF], the sole other member of subtribe Cryptostilidinae [START_REF] Chase | An updated classification of Orchidaceae[END_REF] from South-east Asia and the Pacific, including New Caledonia.

ARECALES, Arecaceae

The taxonomic updates by [START_REF] Pintaud | A revision of the palm genera (Arecaceae) of New Caledonia[END_REF], associated with a complete generic-level phylogenetic analysis of the family [START_REF] Baker | Complete generic-level phylogenetic analyses of Palms (Arecaceae) with comparisons of supertree and supermatrix approach[END_REF], resulted in a significant decrease in the number of palm genera in New Caledonia, placing in synonymy six endemic genera. More recently, Pritchardiopsis Becc. (monotypic) was placed in synonymy with Saribus Blume [START_REF] Bacon | Saribus resurrected[END_REF][START_REF] Bacon | Miocene dispersal drives island radiations in the palm tribe Trachycarpeae (Arecaceae)[END_REF], that occurs in South-east Asia and the Pacific. There are currently eight endemic palm genera recognized in New Caledonia, all members of tribe Areceae. Subtribe Clinospermatinae are endemic to New Caledonia and is composed of Clinosperma Becc. (4/4) and Cyphokentia Brongn (2/2). The study by Baker et al. (2011)

POALES, Poaceae

The dwarf bamboo Greslania Balansa (2/3) has been recovered with strong support as sister to an Australasian clade composed of Cyrtochloa S.Dransf., Dinochloa Buse, Mullerochloa K.M.Wong, Neololeba Widjaja, Parabambusa Widjaja, Pinga Widjaja and Sphaerobambos S.Dransf. [START_REF] Chokthaweepanich | Phylogenetics and evolution of the Paleotropical woody bamboos (Poaceae: Bambusoideae: Bambuseae)[END_REF].

EUDICOTS PROTEALES, Proteaceae

In a molecular phylogenetic tree including all genera of Proteaceae [START_REF] Sauquet | Contrasted patterns of hyperdiversifaction in Mediterreanean hotspots[END_REF], Beaupreopsis Virot (monotypic) formed a strongly supported clade with the Tasmanian genus Cenarrhenes Labill. (monotypic) and the Malagasy genus Dilobeia Thou. (two species), and the last two are moderately supported as sister groups. Beauprea Brongn. & Gris (9/13) is monophyletic [START_REF] He | Pre-Gondwanan-breakup origin of Beauprea (Proteaceae) explains its historical presence in New Caledonia and New Zealand[END_REF] and is strongly supported as the sister lineage to tribe Proteeae (Protea L. and Faurea Harv. from Africa;[START_REF] Sauquet | Contrasted patterns of hyperdiversifaction in Mediterreanean hotspots[END_REF]. The two species of New Caledonian Knightia R.Br. are not related to the type species of this genus from New Zealand and are instead placed in an endemic genus Eucarpha (R.Br.) Spach (1/2) by [START_REF] Weston | A new suprageneric classification of the Proteaceae, with an annotated checklist of genera[END_REF], although the nomenclatural combinations have never been published. Eucarpha is strongly supported as the sister group to the eastern Australian Triunia L.A.S.Johnson & B.G.Briggs [START_REF] Sauquet | Contrasted patterns of hyperdiversifaction in Mediterreanean hotspots[END_REF]. Kermadecia Brongn. & Gris (3/4) and Sleumerodendron Virot (monotypic) are part of a well-supported subtribe Gevuininae [START_REF] Mast | A smaller Macadamia from a more vagile tribe: inference of phylogenetic relationships, divergence times, and diaspore evolution in Macadamia and relatives (tribe Macadamieae; Proteaceae)[END_REF] in which they form a well-supported clade with Turrillia A.C.Sm. (1/3, Fiji, Vanuatu). There is a weak support for a sister relationship between Turrillia and Kermadecia, which are in turn sister to Sleumerodendron [START_REF] Mast | A smaller Macadamia from a more vagile tribe: inference of phylogenetic relationships, divergence times, and diaspore evolution in Macadamia and relatives (tribe Macadamieae; Proteaceae)[END_REF]. The species of these three morphologically close genera [START_REF] Virot | Protéacées. In: Aubréville A, ed. Flore de la Nouvelle-Calédonie et Dépendances[END_REF][START_REF] Smith | Studies of Pacific Island plants. XXIX. Bleasdalea and related genera of Proteaceae[END_REF]

Moraceae

In a molecular phylogenetic analysis including 32 of 37 genera of Moraceae, [START_REF] Zerega | Biogeography and divergence times in the mulberry family (Moraceae)[END_REF] found strong support for a sister relationship between the New Caledonian endemic Sparattosyce Bureau (1/2) and the New Guinean Antiaropsis K.Schum (two species).

FAGALES, Myricaceae

In a molecular phylogenetic analysis including all genera of Myricaceae, [START_REF] Herbert | Nuclear and plastid DNA sequences confirm the placement of the enigmatic Canacomyrica monticola in Myricaceae[END_REF] found strong support for a placement of Canacomyrica Guillaumin (monotypic) as the sister group to the rest of this widespread family.

CELASTRALES, Celastraceae

In a phylogenetic study including all genera of tribe Celastreae [START_REF] Simmons | Phylogeny of the Celastreae (Celastraceae) and the relationships of Catha edulis (qat) inferred from morphological characters and nuclear and plastid genes[END_REF], (2/4) is sister to Hypsophila F.Muell., also from Queensland [START_REF] Coughenour | Phylogeny of Celastraceae subfamily Salacioideae and tribe Lophopetaleae inferred from morphological characters and nuclear and plastid genes[END_REF]Simmons et al., 2012b). Peripterygia Loes. (monotypic) forms a weakly supported clade with the Australasian Siphonodon Griff. and Crossopetalum P.Browne (West Indies, Africa), but their exact relationships are unresolved (Simmons et al., 2012a).

Salaciopsis

OXALIDALES, Cunoniaceae

In a phylogenetic study including all but two genera of Cunoniaceae, Codia J.R.Forst. & G.Forst. is recovered with strong support as the sister group to the Australian Callicoma Andrews [START_REF] Hopkins | Karrabina gen. nov (Cunoniaceae), for the Australian species previously placed in Geissois, and a synopsis of genera in the tribe Geissoieae[END_REF] and is probably monophyletic (15/15, Pillon et al., 2009a;Pillon pers. obs.). The phylogenetic position of Hooglandia McPherson & Lowry (monotypic) is unresolved somewhere among the early branches of the phylogenetic tree for Cunoniaceae [START_REF] Sweeney | Phylogenetic position of the New Caledonian endemic genus Hooglandia (Cunoniaceae) as determined by maximum parsimony analysis of chloroplast DNA[END_REF][START_REF] Hopkins | Karrabina gen. nov (Cunoniaceae), for the Australian species previously placed in Geissois, and a synopsis of genera in the tribe Geissoieae[END_REF][START_REF] Hopkins | Cunoniaceae: Flore de la Nouvelle-Calédonie[END_REF]. The latter genus has some morphological affinities with Aistopetalum Schltr. [START_REF] Mcpherson | Hooglandia, a newly discovered genus of Cunoniaceae from New Caledonia[END_REF]H.C. Hopkins, pers. comm.), a genus of two species occurring in New Guinea that has not yet been included in any molecular phylogenetic study. Pancheria Brongn. & Gris (3/27) is placed in tribe Cunonieae and its relationship to Cunonia L. (New Caledonia, southern Africa) and Weinmannia L. (pantropical) is unclear, although it might be sister to both [START_REF] Bradford | Molecular phylogenetics and morphological evolution in Cunonieae (Cunoniaceae)[END_REF].

MALPIGHIALES Clusiaceae

In a phylogenetic study including all but one genus of Clusiaceae, [START_REF] Ruhfel | Phylogeny of the clusioid clade (Malpighiales): evidence from the plastid and mitochondrial genomes[END_REF] recovered Montrouziera Pancher ex Planch. & Triana (2/6) as sister group to the South American Platonia Raf. with low support.

Salicaceae

In a phylogenetic study of former Flacourtiaceae [START_REF] Alford | Systematics studies in Flacourtiaceae[END_REF], Lasiochlamys Pax & K.Hoffm. (1/11) was found to be nested in Xylosma G.Forst. (America, Asia and Pacific).

However, because the single species sampled, L. reticulata Pax & K.Hoffm., was sister to a Xylosma sp. from New Caledonia (X. vincentii Guillaumin), the author thought there might be a possible misidentification or a possible plastid capture confounding the phylogenetic signal.

Lasiochlamys differs from Xylosma in having petals [START_REF] Lescot | Flore de la Nouvelle-Calédonie et Dépendances[END_REF], but otherwise the two genera are similar and the presence/absence of petals has been shown to be highly homoplasious in this family [START_REF] Alford | Systematics studies in Flacourtiaceae[END_REF].

Euphorbiaceae

In the analysis of [START_REF] Horn | Phylogenetics and the evolution of major structural characters in the giant genus Euphorbia L. (Euphorbiaceae)[END_REF] including all the genera of tribe Euphorbieae, the monotypic Neoguillauminia Croizat is sister to the Australian Calycopeplus Planch. (five species) and these two genera are in turn sister to the large genus Euphorbia L. In the study of [START_REF] Tokuoka | Molecular phylogenetic analysis of Euphorbiaceae sensu stricto based on plastid and nuclear DNA sequences and ovule and seed character evolution[END_REF], Cocconerion Baill. (1/2) is sister to Baloghia Endl. (Australia, New Caledonia, Norfolk and Lord Howe Islands). The distinction between the two genera may warrant further investigations. Bocquillonia Baill. (1/14) is nested with strong support in the pantropical Alchornea Sw. [START_REF] Wurdack | Molecular phylogenetic analysis of uniovulate Euphorbiaceae (Euphorbiaceae sensu stricto) using plastid rbcL and trnL-F DNA sequences[END_REF], although the latter study included a single species of Bocquillonia and two of Alchornea. [START_REF] Webster | Synopsis of the genera and suprogeneric taxa of Euphorbiaceae[END_REF] thought that most genera of subtribe Alchorneinae are only weakly separated from Alchornea. Myricanthe Airy Shaw (monotypic) has never been included in any molecular phylogenetic study and was classified as a close relative to Cocconerion, the Australian Bertya Planch. and the Bornean endemic Borneodendron Airy Shaw based on morphological similarities [START_REF] Webster | Synopsis of the genera and suprogeneric taxa of Euphorbiaceae[END_REF].

Picrodendraceae

In the analysis of [START_REF] Tokuoka | Phylogenetic analyses of Malpighiales using plastid and nuclear DNA sequences, with particular reference to the embryology of Euphorbiaceae sens. str[END_REF] including only four genera of Picrodendraceae (out of c. 24), Scagea McPherson (1/2) is sister to the rest of the family. Longetia Baill.

(monotypic) has not yet been included in any molecular phylogenetic studies.

MYRTALES, Myrtaceae

Carpolepis (J.W.Dawson) J.W.Dawson (3/3) is nested in Metrosideros Banks ex Gaertn. [START_REF] Wright | Phylogenetic analyses of New Caledonian Metrosideros and Carpolepis (Myrtaceae) from nrDNA (ITS) sequences[END_REF][START_REF] Pillon | An expanded Metrosideros (Myrtaceae) to include Carpolepis and Tepualia based on nuclear genes[END_REF], a genus widespread across the Pacific Islands (including New Caledonia), of which it is now considered a synonym [START_REF] Pillon | An expanded Metrosideros (Myrtaceae) to include Carpolepis and Tepualia based on nuclear genes[END_REF]. Cloezia Brongn. & Gris (1/6) is placed with strong support with tribe Tristanieae (Australasia, [START_REF] Biffin | Evolution of exceptional species richness among lineages of fleshy-fruited Myrtaceae[END_REF], although its exact sister group has not been identified, but it may be sister to the entire tribe. In the analysis by [START_REF] Snow | Morphological and molecular evidence of polyphyly in Rhodomyrtus (Myrtaceae: Myrteae)[END_REF] [START_REF] Thornhill | Interpreting the modern distribution of Myrtaceae using a dated molecular phylogeny[END_REF]. Tribe Xanthostemoneae is composed of three genera all represented in New Caledonia [Pleurocayptus Brongn. & Gris (two species), Purpureostemon Gugerli (monotypic) and the much larger Xanthostemon F.Muell. (also Australia, New Guinea, Philippines, eastern Indonesia and Solomon Islands)]. The first two have never been included in any molecular phylogenetic analysis and morphological data suggest that Pleurocalyptus could be nested in Xanthostemon [START_REF] Wilson | The families and genera of vascular plants[END_REF].

CROSSOSOMATALES, Strasburgeriaceae

The monospecific genus Strasburgeria Baill., once considered the sole member of Strasburgeriacae, has been recovered as sister to the New Zealand endemic Ixerba A.Cunn. [START_REF] Cameron | On the phylogenetic position of the New Caledonian endemic families Paracryphiaceae, Oncothecaceae, and Strasburgeriaceae: a comparison of molecules and morphology[END_REF] in the poorly known order Crossossomatales.

SAPINDALES

Sapindaceae

Sapindaceae are highly diverse in New Caledonia with four endemic genera: Gongrodiscus Radlk. (3/3), Loxodiscus Hook.f. (monotypic), Podonephelium Baill. (7/9), and Storthocalyx Radlk. (4/5). [START_REF] Buerki | Phylogenetic inference of New Caledonian lineages of Sapindaceae: molecular evidence requires a reassessment of generic circumscriptions[END_REF] have formally tested the monophyly and phylogenetic relationships of these endemic genera by including representatives into a generic level phylogenetic analysis of Sapindaceae [START_REF] Buerki | Plastid and nuclear DNA markers reveal intricate relationships at subfamilal and tribal levels in the soapberry family (Sapindaceae)[END_REF]. This study confirmed the monophyly of all the endemic genera, which belong to two different phylogenetic lineages: the Cupania L. group (Sapindoideae) and the Dodonaea Mill. group (Dodonaeoideae). In the Oxanthera Montrouz. (2/5) is nested in the large genus Citrus L. [START_REF] Bayer | A molecular phylogeny of the orange subfamily (Rutaceae: Aurantioideae) using nine cpDNA sequences[END_REF]. Boronella Baill. (2/4) is nested in the Australian Boronia Sm. [START_REF] Bayly | Major clades of Australasian Rutoideae (Rutaceae) Based on rbcL and atpB sequences[END_REF] and its species have now been transferred into this genus [START_REF] Bayly | Transfer of the New Caledonian genus Boronella to Boronia (Rutaceae) based on analyses of cpDNA and nrDNA[END_REF]. Crossosperma [START_REF] Beaumont | Gnidia (Thymelaeaceae) is not monophyletic: taxonomic implications for Thymelaeoideae and a partial new generic taxonomy for Gnidia[END_REF].

SANTALALES Balanophoraceae

In a phylogenetic study of Balanophoraceae, Hachettea Baill. (monotypic) was recovered as sister to the New Zealand endemic Dactylanthus Hook.f. [START_REF] Su | Phylogenetic relationships of Santalales with insights into the origins of holoparasitic Balanophoraceae[END_REF].

Santalaceae

In a phylogenetic analysis including all of the accepted genera of Santalaceae [START_REF] Der | A molecular phylogeny of Santalaceae (Santalales)[END_REF], Amphorogyne Stauffer & Hurlim. (1/3) and Daenikera Hurlim. & Stauffer (monotypic) are retrieved as sister and inferred as sister to the rest of tribe Amphorogyneae.

Elaphanthera N. Hallé (monotypic) was considered as a synonym of Exocarpos Labill.

(South-east Asia and Pacific) by [START_REF] Der | A molecular phylogeny of Santalaceae (Santalales)[END_REF], but the single species of this genus

has not yet been included in a molecular phylogenetic framework.

ASTERIDS

ERICALES

Sapotaceae

Since the earliest monograph was published [START_REF] Aubréville | Sapotacées. In: Aubréville A, ed. Flore de la Nouvelle-Calédonie et Dépendances[END_REF], New Caledonian Sapotaceae have been the subject of major generic rearrangements over the past few years [START_REF] Bartish | Phylogenetic relationships among New Caledonian Sapotaceae (Ericales): molecular evidence for generic polyphyly and repeated dispersal[END_REF][START_REF] Swenson | Phylogenetic and generic limits in the Niemeyera complex of New Caledonian Sapotaceae: evidence of multiple origins of the anisomerous flower[END_REF][START_REF] Swenson | Towards a natural classification of Sapotaceae subfamily Chrysophylloideae in Oceania and Southeast Asia based on nuclear sequence data[END_REF] and several genera once considered as endemic to New Caledonia have been placed in synonymy (Corbassona Aubrév., Leptostylis Benth., Ochrothallus Pierre ex Baill., Pyriluma Aubrév., Sebertia Pierre ex Engl. and Trouettia Pierre ex Baill.) or now include species from outside New Caledonia (Pichonia Pierre). The expanded Pycnandra Benth. has emerged as the largest endemic genus of New Caledonia with 59 described species. It is sister to the Australian Niemeyera F.Muell. [START_REF] Swenson | Towards a natural classification of Sapotaceae subfamily Chrysophylloideae in Oceania and Southeast Asia based on nuclear sequence data[END_REF] and a study including 60 of 68 presumed species (some undescribed) indicated that it is monophyletic [START_REF] Swenson | Island lifeclassification, speciation and cryptic species of Pycnandra (Sapotaceae) in New Caledonia[END_REF].

Primulaceae

The recently described monotypic genus Mangenotiella M.Schmid [START_REF] Schmid | Contribution to the knowledge of Primulaceae (ex Myrsinaceae) of New Caledonia. III. Tapeinosperma Hook.f. and Mangenotiella gen. nov. genera[END_REF] has not yet been included in any phylogenetic study. There has been little phylogenetic work on woody Primulaceae (but see [START_REF] Strijk | Timing and tempo of evolutionary diversification in a biodiversity hotspot: Primulaceae on Indian Ocean islands[END_REF], and Mangenotiella needs to be critically compared with Tapeinosperma Hook.f. (also present in New Caledonia) and Discocalyx Mez (South-east Asia to Pacific), the distinctness of which has been questioned (e.g. [START_REF] Smith | Studies of Pacific Island plants, XXV. the Myrsinaceae of the Fijian region[END_REF].

Ericaceae

The phylogenetic relationships between Cyathopsis Brongn. & Gris (1/3) and a number of other genera of the Styphelieae are unresolved [START_REF] Quinn | Generic concepts in Styphelieae (Ericaceae): the Cyathodes group[END_REF][START_REF] Puente-Lelièvre | A five-marker molecular phylogeny of the Styphelieae (Epacridoideae, Ericaceae) supports a broad concept of Styphelia[END_REF], although an analysis based on the nuclear ITS region alone suggests a weakly supported sister relationship with the Australian Lissanthe R.Br.

ICACINALES, Oncothecaceae

Oncotheca Baill. (1/2) is the only genus of Oncothecaceae. Oncothecaceae were not placed in any order in APG [START_REF] Apg Iii | An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III[END_REF], because most phylogenetic studies had failed to clarify an exact position in lamiids [START_REF] Bremer | Phylogenetics of asterids based on 3 coding and 3 non-coding chloroplast DNA markers and the utility of non-coding DNA at higher taxonomic levels[END_REF][START_REF] Cameron | On the phylogenetic position of the New Caledonian endemic families Paracryphiaceae, Oncothecaceae, and Strasburgeriaceae: a comparison of molecules and morphology[END_REF][START_REF] González | Metteniusaceae, an early-diverging family in the lamiid clade[END_REF][START_REF] Soltis | Angiosperm phylogeny: 17 genes, 640 taxa[END_REF][START_REF] Byng | Phylogenetic relationships of Icacinaceae focusing on the vining genera[END_REF].A recent study using complete plastid genomes recovered this genus as sister to a narrowly defined Icacinaeae [START_REF] Stull | Resolving basal lamiid phylogeny and the circumscription of Icacinaceae with a plastome-scale data set[END_REF] and it was placed in Icacinales in APG IV (2016) to reflect this finding.

GENTIANALES

Rubiaceae

Morierina Vieill. (2/2) and Thiollierea Montrouz. (12/12, previously included under Bikkia Reinw., but reinstated by [START_REF] Barrabé | Reinstatement of the endemic New Caledonian genus Thiollierea Montrouz. (Rubiaceae) necessitated by the polyphyly of Bikkia Reinw. as currently circumscribed[END_REF], form a well-supported clade, sister to an alliance of several Caribbean genera mainly occurring in Cuba with high support (Ceratopyxis Hook.f., Eosanthe Urb., Phialanthus Griseb. and Schmidtottia Urb.; [START_REF] Manns | Towards a better understanding of intertribal relationships and stable tribal delimitations within Cinchonoideae s.s. (Rubiaceae)[END_REF].

Although [START_REF] Manns | Towards a better understanding of intertribal relationships and stable tribal delimitations within Cinchonoideae s.s. (Rubiaceae)[END_REF] placed Morierina montana Vieill. as sister to two Thiollierea spp., uncertainties remain about the internal topology of the 'Morierina-Thiollierea' clade since an unpublished study, based on a complete species sampling and five DNA loci, has shown unresolved interspecific and intergeneric relationships (Mouly, pers. comm.). Guettarda L. has been revealed to be polyphyletic [START_REF] Achille | Polyphyly in Guettarda L. (Rubiaceae, Guettardeae) based on nrDNA ITS sequence data[END_REF]. Of the 20 New Caledonian species, only the type species G. speciosa L. belongs to Guettarda s.s. The other species should be included in Antirhea Juss., Guettardella Benth., Timonius DC., Tinadendron Achille and a new endemic genus, Gea Achille ined. (2/6). Robust morphological characters support the last genus, composed of six species (Achille, pers. comm.), although this genus is unpublished and its monophyly has not been demonstrated.

The monotypic Normandia Hook.f. was found to be nested in Coprosma J.R.Forst. & G.Forst. [START_REF] Anderson | Molecular phylogeny of the tribe Anthospermeae (Rubiaceae): systematic and biogeographic implications[END_REF], but this study was based on an incorrect DNA sequence [START_REF] Markey | Coprosma talbrockiei: an oddball sheds light on the Coprosminae[END_REF]. Recently, Normandia has been excluded from this genus with strong support and placed as the possible sister-group of the large alliance formed by Coprosma and Nertera Gaertn. [START_REF] Markey | Coprosma talbrockiei: an oddball sheds light on the Coprosminae[END_REF][START_REF] Cantley | Biogeographic insights on Pacific Coprosma (Rubiaceae) indicate two colonizations to the Hawaiian Islands[END_REF].

Apocynaceae

In the analysis of [START_REF] Potgieter | Phylogenetic relationships within Apocynaceae s.l. based on trnL intron and trnL-F spacer sequences and propagule characters[END_REF], Cerberiopsis Vieill. ex Pancher & Sebert (1/3) is strongly supported as sister to Cerbera L. (Indian Ocean, Australasia, Pacific). [START_REF] Livshultz | Phylogeny of Apocynoideae and the APSA clade (Apocynaceae s.l.)[END_REF] found Artia Guillaumin (1/4) to be sister to the Australasian Parsonsia R.Br. noting the similarities between the two genera and acknowledging that only a few Parsonsia spp.

were included in the phylogenetic analysis. The two genera are in turn nested in the Neotropical Prestonia R.Br. Therefore, generic delimitations need to be further evaluated in this group. Artia was not considered as an endemic genus in [START_REF] Morat | The taxonomic reference base Florical and characteristics of the native vascular flora of New Caledonia[END_REF], but this was an error.

LAMIALES, Gesneriaceae

In a phylogenetic analysis including all of the genera of tribe Coronanthereae, [START_REF] Woo | New World origins of southwest Pacific Gesneriaceae: multiple movements across and within the South Pacific[END_REF] found that Depanthus S.Moore (1/2) was either sister to the Australian Lenbrassia G.W.Gillett or to the Lord Howe island endemic Negria F.Muell.

AQUIFOLIALES, Stemonuraceae

Gastrolepis Tiegh. (two species) has not yet been included in any molecular phylogenetic analysis.

ASTERALES Alseuosmiaceae

In a phylogenetic analysis published by [START_REF] Lundberg | A phylogenetic study of the order Asterales using one morphological and three molecular data sets[END_REF] Platyspermation Guillaumin (monotypic) was inferred as sister to the rest of the family (four out of five genera included). Periomphale Baill. (monotypic) was once synonymized with Wittsteinia F.Muell., a view latter rejected by [START_REF] Tirel | Flore de la Nouvelle-Calédonie et Dépendances[END_REF]. Unpublished phylogenetic analyses support the latter conclusion (A. Mouly, pers. comm.).

Phellinaceae

Phelline Labill. (3/14) is the only genus of Phellinaceae, which form a clade with Alseuosmiaceae and Argophyllaceae in Asterales [START_REF] Kårehed | Evolution of the Autralasian families Alseuosmiaceae, Argophyllaceae, and Phellinaceae[END_REF]. The relationships between these three small and poorly known families are unclear. Phellinaceae were placed with strong support as sister to Argophyllaceae in the analysis of [START_REF] Tank | Phylogeny and phylogenetic nomenclature of the Campanulidae based on an expanded sample of genes and taxa[END_REF], but in the analysis of [START_REF] Soltis | Angiosperm phylogeny: 17 genes, 640 taxa[END_REF] including more DNA regions, they were placed as sister to a weakly supported clade including Alseuosmiaceae and Argophyllaceae.

PARACRYPHIALES, Paracryphiaceae

Paracryphia Baker f. (monotypic) was once considered as the sole member of Paracryphiaceae, which has been expanded to include Sphenostemon Baill. and Quintinia

A.DC. (APG III, 2009

). There is strong support for a sister-group relationship between Paracryphia and Sphenostemon from Australia, New Guinea and New Caledonia [START_REF] Tank | Phylogeny and phylogenetic nomenclature of the Campanulidae based on an expanded sample of genes and taxa[END_REF][START_REF] Soltis | Angiosperm phylogeny: 17 genes, 640 taxa[END_REF]. Current phylogenetic evidence suggests that the monophyly of 30 New Caledonian endemic genera still needs to be confirmed or has been challenged (Table 1) and eight are clearly nested in larger, more widespread genera; some have been synonymized since [START_REF] Morat | The taxonomic reference base Florical and characteristics of the native vascular flora of New Caledonia[END_REF]. In most problematic cases, the endemic genera are nested in a larger more widespread genus (e.g. Neocallitropsis nested in Callitris, and Comptonella, Dutaillyea and Picrella in Melicope) or their distinction from such genera needs further testing (e.g. Lasiochlamys vs. Xylosma, Kibaropsis vs. Hedycarya). This latter situation mirrors previous results obtained from the New Zealand flora (Garnock-Jones, 2014) and matches the expectations of [START_REF] Stuessy | Paraphyly and endemic genera of oceanic islands: implications for conservation[END_REF]. In several cases, the evidence that an endemic genus is nested in a larger one has been known for a long time (e.g. Oxanthera nested in Citrus), but the synonymy and the necessary taxonomic changes are still pending. There are currently few cases of endemic genera that are polyphyletic (the recently described Kanakomyrtus and potentially Chambeyronia and Kentiopsis). Although many species in endemic genera are yet to be included in phylogenetic studies to confirm monophyly, the small size of most endemic genera makes polyphyly unlikely. In a few cases, some endemic genera may be better merged, although further evidence may still be required (e.g. Thiollierea/Morierina, Chambeyronia/Actinokentia/Kentiopsis, Kermadecia/Sleumerodendron). The distinctiveness and monophyly of eight genera remain to be evaluated by molecular analyses.

APIALES

The flora of New Caledonia is still incompletely known as indicated by its increasing number of known endemic species over time: 2423 [START_REF] Jaffré | Composition and characterisation of the native flora of New Caledonia[END_REF], 2519 [START_REF] Morat | The taxonomic reference base Florical and characteristics of the native vascular flora of New Caledonia[END_REF] and 2544 [START_REF] Munzinger | FLORICAL: checklist of the vascular indigeneous flora of New Caledonia vers[END_REF]. Many important families in New Caledonia have not yet been monographed in the local flora "Flore de la Nouvelle-Calédonie" or elsewhere.

As for other tropical areas, herbaria around the world probably house a large number of New Caledonian species awaiting description [START_REF] Bebber | Herbaria are a major frontier for species discovery[END_REF] and this may include a few novel genera. Future phylogenetic works may also reveal new endemic genera to be resurrected or described, e.g. the recently segregated Jaffrea (Rhamnaceae) or, in Sapindaceae, the New Caledonian species of the Palaeotropical Arytera and Cupaniopsis appear to be phylogenetically distinct [START_REF] Buerki | Phylogenetic inference of New Caledonian lineages of Sapindaceae: molecular evidence requires a reassessment of generic circumscriptions[END_REF]. As increasing knowledge is gathered regarding the phylogenetic relationships of the endemic genera, critical morphological comparison with their closest relatives becomes easier. Some of the monotypic genera may lose their rank to reduce redundancy similar to the expanded concepts of Strasburgeriaceae and Paracryphiaceae (Angiosperm Phylogeny Group III, 2009) that reduced the number of endemic families from five to three.

Current evidence indicates that between 62 and 91 genera endemic to New Caledonia probably satisfy the criterion of monophyly (Table 1) and this probably represents a conservative estimate of the actual number of endemic genera. These genera have on average 4.7-4.9 species, with a median of 2; 26-35 of them are monotypic and they encompass 12.0-16.7% of the endemic flora of New Caledonia.

Comparison of the New Caledonian endemic generic flora with those of other Pacific islands New Zealand may have between 28 and 44 endemic genera after considering phylogenetic evidence (Garnock-Jones, 2014). Eastern Polynesia (French Polynesia and the Cook Islands) has 12 endemic genera according to [START_REF] Meyer | Threat of invasive alien plants to native flora and forest vegetation of eastern Polynesia[END_REF]; however, the endemic Sclerotheca A.DC. and Apetahia Baill. (Campanulaceae) may be merged since Sclerotheca is nested in Apetahia [START_REF] Givnish | Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae)[END_REF]Pillon et al. unpublished) and are morphologically similar [START_REF] Florence | New species of Plakothira (Loasaceae), Melicope (Rutaceae), and Apetahia (Campanulaceae) from the Marquesas Islands[END_REF]. The endemic Tahitia Burret (Malvaceae) may be considered as a synonym of Christiana DC. [START_REF] Kubitzki | Asterophorum and Tahitia congeneric with Christiana[END_REF] and Plakothira J.Florence (Loasaceae) is nested in Klaprothia Kunth [START_REF] Weigend | A preliminary phylogeny of Loasaceae subfam. Loasoideae (Angiospermae: Cornales) based on trnL sequence data, with consequences for systematics and historical biogeography[END_REF]. Samoa has only two endemic genera according to [START_REF] Whistler | The rare plants of Samoa[END_REF]: Sarcopygme Setch. & Christoph. (Rubiaceae) and Solfia Rechinger (Arecaceae). However, recent phylogenetic evidence challenged their distinctiveness so that the first genus is now a synonym of Morinda L. [START_REF] Razafimandimbison | Nomenclatural changes and taxonomic notes in the tribe Morindeae (Rubiaceae)[END_REF] and the second is a synonym of Balaka Becc. [START_REF] Zona | Solfia transferred to Balaka[END_REF]. Fiji has seven endemic genera according to Flora Vitiensis Nova [START_REF] Smith | Flora Vitiensis nova: a new flora of Fiji (spermatophytes only)[END_REF] is nested in Soulamea Lam. [START_REF] Clayton | Molecular phylogeny of the tree-ofheaven family (Simaroubaceae) based on chloroplast and nuclear markers[END_REF] and Pimia is a synonym of Commersonia J.R.Forst. & G.Forst. [START_REF] Dorr | The identity and typification of Pimia Seem. (Sterculiaceae)[END_REF]. Gillespiea has never been included in any molecular study, Hedstromia belongs to a large Psychotria L. clade the limits of which remain unclear and requires further work [START_REF] Barrabé | New Caledonian lineages of Psychotria (Rubiaceae) reveal different evolutionary histories and the largest documented plant radiation for the archipelago[END_REF] and Squamellaria is a peculiar lineage of subtribe Hydnophytinae and is now considered to be present on Vanuatu and the Solomon Islands [START_REF] Chomicki | Evolutionary relationships and biogeography of the antepiphytic genus Squamellaria (Rubiaceae: Psychotrieae) and their taxonomic implications[END_REF]. Sukunia, sometimes considered as a synonym of Atractocarpus Schltr. & K.Krause [START_REF] Puttock | Generic concepts in Australian Gardenieae (Rubiaceae): a cladistic approach[END_REF], was viewed as distinct more recently [START_REF] Mouly | Phylogenetic structure and clade circumscriptions in the Gardenieae complex (Rubiaceae)[END_REF]. Note that Degeneriacae are endemic to Fiji. There is no conspectus for the flora of Vanuatu, but it seems to host only one endemic genus: Carpoxylon H.Wendl. & Drude (Arecaceae). We still lack a flora treatment for the Solomon islands, but [START_REF] Thorne | Floristic relationships between New Caledonia and the Solomon Islands[END_REF] Cassidispermum is thought to be a synonym of Burckella Pierre [START_REF] Govaerts | World checklist of Sapotaceae[END_REF], Rehderophoenix is a synonym of Drymophloeus Zipp. and Strongylocaryum is a synonym of Ptychosperma Labill. [START_REF] Govaerts | World checklist of Arecaceae. Facilitated by the Royal Botanic Gardens[END_REF]. The Hawaiian islands have 35 endemic vascular plant genera [START_REF] Wagner | Manual of the flowering plants of Hawai'i[END_REF][START_REF] Palmer | Hawai'i's ferns and fern allies[END_REF], a number that needs to be revised and should be considered as an upper estimate. [START_REF] Stuessy | Paraphyly and endemic genera of oceanic islands: implications for conservation[END_REF] suggested that only 22 may be recognized after careful examination.

Most Pacific archipelagos have only a few endemic genera, the number tending to decrease with the progress of phylogenetic analyses. Larger numbers are found in New Caledonia, New Zealand and Hawaii. Even when considering lower estimates, New Caledonia still has by far the largest number of endemic genera in the Pacific region. It also has three endemic families (and one order, Amborellales); only Fiji also has an endemic family.

Why are there so many endemic genera in New Caledonia? New Caledonia has a rich and unique flora [START_REF] Morat | The taxonomic reference base Florical and characteristics of the native vascular flora of New Caledonia[END_REF] with 3389 species, of which 75.1% are endemic [START_REF] Munzinger | FLORICAL: checklist of the vascular indigeneous flora of New Caledonia vers[END_REF]. It can therefore also be expected to have a higher number of endemic genera. These two levels of endemism may share a number of identical causes. New Caledonia is geographically isolated, has a relatively large surface (c. 18,600 km²) and is chiefly composed of a single large island (rather than many small ones) and might therefore be expected to harbour more species than an archipelago of equivalent surface, but composed of a greater number of smaller islands [START_REF] Diamond | The island dilemma: lessons of modern biogeographic studies for the design of natural reserves[END_REF]. It also lies entirely in the tropical belt, compared to, e.g., New Zealand, which is at a higher latitude and can be expected to have a comparatively less species-rich flora [START_REF] Gaston | Global patterns in biodiversity[END_REF]. Beyond such trivial explanations, there may be other factors that have favoured a greater accumulation of endemic genera in New Caledonia than in any other Pacific islands.

Endemic genera as relicts

Endemic genera may be relicts of larger and once widespread clades, in which species from outside the island may have been driven to extinction and New Caledonia may have offered particular conditions to accumulate many such relicts. Indeed, 26 to 35 of these genera are monotypic and most of them have few species (only eight to 12 have ten or more species), suggesting that they may be declining globally rather than actively diversifying. Several endemic genera have a sister group in remote areas (South Africa, South America, Caribbean) that do not seem to be intuitive source areas for the New Caledonian flora. Such biogeographical disjunctions may be easier to explain by extinctions in areas adjacent to New Caledonia.

Although its biodiversity may not be as old as it was previously estimated, New Caledonia is still much older than any other islands in the Pacific region besides New Zealand (Table 2). Communities on New Caledonia may have had sufficient time to reach saturation as indicated by slowing-down of diversification and density-dependent diversification observed in several groups [START_REF] Espeland | Diversity dynamics in New Caledonia: towards the end of the museum model?[END_REF][START_REF] Pillon | Time and tempo of diversification in the flora of New Caledonia[END_REF][START_REF] Swenson | Island lifeclassification, speciation and cryptic species of Pycnandra (Sapotaceae) in New Caledonia[END_REF].

There is, however, not yet any evidence from molecular dating [START_REF] Pillon | Time and tempo of diversification in the flora of New Caledonia[END_REF] or the fossil record (which is sparse and requires a critical review; [START_REF] Guillaumin | Notes de paléobotanique néo-calédonienne[END_REF] supporting the continuous coverage of vegetation since the emergence of the island in the Eocene.

Nevertheless, rainforests may have been continuously present for a long period of time, including through the Quaternary climatic oscillations [START_REF] Pintaud | Chorology of New Caledonian palms and possible evidence of Pleistocene rain forest refugia[END_REF][START_REF] Poncet | Phylogeography and niche modelling of the relict plant Amborella trichopoda (Amborellaceae) reveal multiple Pleistocene refugia in New Caledonia[END_REF][START_REF] Pouteau | New Caledonia: a Pleistocene refugium for rain forest lineages of relict angiosperms[END_REF]. In contrast, nearby Australia, which probably served as a source for most of the island flora [START_REF] Morat | Our knowledge of the flora of New Caledonia: endemism and diversity in relation to vegetation types and substrates[END_REF] went through dramatic climatic changes during the Tertiary, particularly aridification, that may have driven to extinction many plant lineages, most notably in the rainforest [START_REF] Holloway | A survey of the Lepidoptera, biogeography, and ecology of New Caledonia[END_REF][START_REF] Byrne | Decline of a biome: evolution, contraction, fragmentation, extinction and invasion of the Australian mesic zone biota[END_REF][START_REF] Crisp | How was the Australian flora assembled over the last 65 million years? A molecular phylogenetic perspective[END_REF][START_REF] Sniderman | Fossil evidence for a hyperdiverse sclerophyll flora under a non-Mediterranean-type climate[END_REF], some of them being putative close relatives of New Caledonian species. Indeed, a number of genera restricted to New Caledonia nowadays have a fossil record in Australia and/or New Zealand: Beauprea [START_REF] Pocknall | Pollen morphology of Beauprea (Proteaceae): modern and fossil[END_REF], Codia [START_REF] Barnes | Macrofossils of Callicoma and Codia (Cunoniaceae) from Australian Cainozoic sediments[END_REF], Amphorogyne, Paracryphia and Phelline [START_REF] Pole | Was New Zealand a primary source for the New Caledonian flora?[END_REF]. New Caledonian conifers also suffered lower extinction rates than in other areas [START_REF] Condamine | Ancient islands acted as refugia and pumps for conifer diversity[END_REF].

New Caledonia is well known for its ultramafic substrates that offer challenging conditions for plant growth and host the unique 'maquis' vegetation [START_REF] Isnard | How did the ultramafic soils shape the flora of the New Caledonian hotspot?[END_REF]. We found that the majority of the endemic genera (59-85) are found on ultramafic substrates and 25-36 of the endemic genera are restricted to them (or almost so), whereas only three to six avoid them (Table 1). Ultramafic substrates cover about one third of New Caledonia and host about half of the indigenous flora; 36% of the species are restricted to this substrate [START_REF] Isnard | How did the ultramafic soils shape the flora of the New Caledonian hotspot?[END_REF]. Therefore, the number of endemic genera restricted to these substrates is unexpectedly high regarding their surface and species richness. Ultramafic substrates probably covered the entire island as it emerged [START_REF] Pelletier | Geology of the New Caledonia region and its implications for the study of the New Caledonian biodiversity[END_REF] and probably acted as ecological filter in the making of this island flora [START_REF] Pillon | Ultramafic soils and species sorting in the flora of New Caledonia[END_REF]. This double insularity may have protected the earliest settlers by limiting the rate of immigration [START_REF] Jaffré | Changements dans la végétation de la Nouvelle-Calédonie au cours du Tertiaire: la végétation et la flore des roches ultrabasiques[END_REF], slowing down the turnover in this community and allowing relicts to survive. The high diversity of conifers in New Caledonia, often considered as less competitive than angiosperms, and their strong bias towards ultramafic substrates [START_REF] Jaffré | Threats to the conifer species found on New Caledonia's ultramafic massifs and proposals for urgently needed measures to improve their protection[END_REF] and the limited number of invasive species recorded on such soils [START_REF] Meyer | Les plantes envahissantes et potentiellement envahissantes dans l'archipel néo-calédonien : premère évaluation et recommendations de gestion[END_REF] support this hypothesis.

Endemic genera as the product of adaptive radiations

Adaptive radiation on islands implies the diversification of one colonizer into an array of species occupying a variety of niches and differing by morphological and physiological traits associated with those niches [START_REF] Schluter | The ecology of adaptive radiation[END_REF]. Carlquist (1965: 134) [START_REF] Kathriarachchi | Phylogenetics of tribe Phyllantheae (Phyllanthaceae; Euphorbiaceae sensu lato) based on nrITS and plastid matK DNA sequence data[END_REF] and Tieghemopanax R.Vig. (now included in Polyscias J.R.Forst. & G.Forst., see [START_REF] Eibl | Evolution of Polyscias sect. Tieghemopanax (Araliaceae) based on nuclear and chloroplast DNA sequence data[END_REF]. When morphological differences are sufficient, the offspring of an adaptive radiation may be treated as different genera, but this does not seem to be common in New Caledonia. Eriaxis and Clematepistephium (both monotypic) have remarkably different habits.

The first is an erect herb not exceeding 50 cm (inflorescence excluded) mostly found in maquis, whereas the second is a long rainforest vine reaching several meters [START_REF] Hallé | Flore de la Nouvelle-Calédonie et dépendances[END_REF].

Clinosperma (four species) and Cyphokentia (two species) differ by the presence/absence of membranous ramenta and didymous/not didymous anthers [START_REF] Pintaud | A revision of the palm genera (Arecaceae) of New Caledonia[END_REF], but these cannot be easily connected with putative ecological differences. Amphorogyne spp. (three) are root parasitic chlorophyllous shrubs and trees reaching several meters, whereas Daenikera (monotypic) is a parasitic, aphyllous, purplish shrub not exceeding 60 cm [START_REF] Hallé | Flore de la Nouvelle-Calédonie et dépendances[END_REF].

Nephrodesmus (19 species) and Arthroclianthus (five species) differ by the position of the corolla wings (cover the keel in Arthroclianthus vs. do not cover the keel in Nephrodesmus), and their fruit morphology (sustained by a stipe vs. not sustained by a stipe; H. Vandrot, comm. pers.). These latter genera do not differ in terms of ecology, although Arthroclianthus has a greater ecological amplitude. Morierina (two species) and Thiollierea (12 species) differ in flower morphology (tubular with long and reflexed lobes vs. campanulate with short lobes), inflorescence structure (straight and subtending on a stiff axis with leafy bracts vs. pendant and generally on a flexible axis without leafy bracts) and type of anthers (not twisted vs. twisted, [START_REF] Barrabé | Reinstatement of the endemic New Caledonian genus Thiollierea Montrouz. (Rubiaceae) necessitated by the polyphyly of Bikkia Reinw. as currently circumscribed[END_REF], suggesting a shift in pollination syndrome (moths vs. birds, [START_REF] Motley | Molecular systematics of the Catesbaeeae-Chiococceae complex (Rubiaceae): flower and fruit evolution and biogeographic implications[END_REF]. The first is mostly found in rainforests, whereas the second is generally in maquis; both are restricted to ultramafic substrates. Kermadecia (four species) and Sleumerodendron (one species) and Turrillia (Vanuatu & Fiji) are similar vegetatively and ecologically and their flowers differ only in small points [START_REF] Virot | Protéacées. In: Aubréville A, ed. Flore de la Nouvelle-Calédonie et Dépendances[END_REF][START_REF] Smith | Studies of Pacific Island plants. XXIX. Bleasdalea and related genera of Proteaceae[END_REF].

These pairs of sister genera account only for a small number of species (24 at most for Arthroclianthus-Nephrodesmus). The morphological and ecological differences are relatively modest in three cases (Clinosperma & Cyphokentia, Arthroclianthus & Nephrodesmus, Kermadecia & Sleumerodendron) and do not obviously qualify as adaptive radiations. The fact that two are relatively species-poor (Clematepistephium & Eriaxis, Amphorogyne & Daenikera) suggests that they are relicts rather than actively diversifying lineages. This contrasts with Hawaii that has several multi-generic plant radiations: the silversword alliance (three genera, 28 species; [START_REF] Baldwin | Adaptive radiation of the Hawaiian silversword alliance: congruence and conflict of phylogenetic evidence from molecular and non-molecular investigations[END_REF], lobeliads (six genera, 126 species; [START_REF] Givnish | Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae)[END_REF] and mints (three genera, 60 species, [START_REF] Lindqvist | Origin of the Hawaiian endemic mints within North American Stachys (Lamiaceae)[END_REF]. The Macaronesian islands have a large radiation of Crassulaceae (four genera, 63 species; [START_REF] Mort | Phylogenetics and evolution of the Macaronesian clade of Crassulaceae inferred from nuclear and chloroplast sequence data[END_REF].

Adaptive radiations seem to have contributed little to the formation of endemic genera in New Caledonia. The largest monophyletic clade in New Caledonia is a group of Psychotria (c. 78 species, [START_REF] Barrabé | New Caledonian lineages of Psychotria (Rubiaceae) reveal different evolutionary histories and the largest documented plant radiation for the archipelago[END_REF] with modest morphological diversity that is not easily correlated with the ecology of the different species. The largest endemic genus, Pycnandra, is composed of six subgenera [START_REF] Swenson | Island lifeclassification, speciation and cryptic species of Pycnandra (Sapotaceae) in New Caledonia[END_REF], most of which were once recognized as genera.

However, apart from subgenus Lepostylis, the delimitation of these subgenera has changed considerably since the time when they were ranked as genera [START_REF] Swenson | Phylogenetic and generic limits in the Niemeyera complex of New Caledonian Sapotaceae: evidence of multiple origins of the anisomerous flower[END_REF]. The homoplasy of most morphological characters explored so far [START_REF] Swenson | Island lifeclassification, speciation and cryptic species of Pycnandra (Sapotaceae) in New Caledonia[END_REF] probably made the classification of this group complicated. Since the subgenera of Pycnandra are difficult to characterize morphologically [START_REF] Swenson | Revision of Pycnandra subgenus Pycnandra (Sapotaceae), a genus endemic to New Caledonia[END_REF][START_REF] Apg Iv | An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV[END_REF][START_REF] Swenson | Island lifeclassification, speciation and cryptic species of Pycnandra (Sapotaceae) in New Caledonia[END_REF] and do not show clear ecological differences, Pycnandra does not seem to be comparable to the multigeneric adaptive radiations from Hawaii or the Macaronesian islands cited above. With the current evidence at hand, most New Caledonian plant lineages may be considered as mere "radiation" or, in a few cases, "explosive radiation" (e.g. Psychotria) rather than "adaptive radiation" [START_REF] Givnish | Adaptive radiation versus 'radiation' and 'explosive diversification': why conceptual distinctions are fundamental to understanding evolution[END_REF].

It remains unclear why the New Caledonian flora has few dramatic examples of adaptive radiation, but it may be linked to the fact that the vegetation is largely composed of woody plant species [START_REF] Virot | La végétation canaque[END_REF], whereas most convincing examples of adaptive radiation in plants are herbaceous or ancestrally herbaceous [START_REF] Givnish | Ecology of plant speciation[END_REF]. "Increased woodiness" is a commonly observed syndrome on islands, whereby herbaceous ancestors become shrubs or trees after colonizing islands [START_REF] Carlquist | Island life[END_REF][Carlquist, (chapter 8), 1974 (chapter 10) (chapter 10)], but this is almost unseen in New Caledonia and the rest of Melanesia (Carlquist, 1974: 409). Many large herbaceous families are under-represented in New Caledonia, including Asteraceae, Campanulaceae, Cyperaceae, Lamiaceae and Poaceae [START_REF] Pillon | Ultramafic soils and species sorting in the flora of New Caledonia[END_REF]. The paucity of Asteraceae is particularly striking, especially on the ultramafic soils (Carlquist, 1965: 42), whereas they are well represented in many island floras, producing several remarkable adaptive radiations (Carlquist, 1965: 204). When New Caledonia emerged, it was probably entirely covered with ultramafic substrate which may have filtered the successful immigrants [START_REF] Pillon | Ultramafic soils and species sorting in the flora of New Caledonia[END_REF] and primarily woody plants may be more competitive than herbs on ultramafic substrates.

The relative ancient age of New Caledonia may also explain the lack of dramatic adaptive radiation by allowing enough time for a diverse cohort of immigrants to reach the island. The diversity of Asteraceae on islands may be explained by their ability to disperse long distances and their weediness and evolutionary lability (Carlquist, 1965: 204), whereas trees may be poor dispersers (Carlquist, 1965: 189). As time passes, even the least likely dispersal might happen and, for example, new immigrant tree species may outcompete those that evolved from herbaceous colonizers. The available data from molecular dating suggest that arrivals of colonizers were spread in time rather than being synchronous and close to the putative emergence time of New Caledonia [START_REF] Pillon | Time and tempo of diversification in the flora of New Caledonia[END_REF]. On New Caledonia, we may be observing a mature flora, in which continuous immigration has progressively thinned out the earlier adaptive radiations. Such processes have not yet taken place in the other more recent Pacific islands.

Despite its complex environmental gradients, New Caledonia may not offer ecological conditions as diverse as other islands, particularly in terms of climate. Hawaiian islands display a diverse range of climatic conditions (Carlquist, 1980: 63), some extreme, offering considerable opportunities for adaptive radiations. New Caledonia lies entirely in the tropical belt and its highest peak (Mt Panié, 1628 m) is lower than that of several Pacific archipelagos (Table 2). Although its mountain tops host some distinctive plant communities that may be exposed to frost [START_REF] Bradford | Plant species microendemism and conservation of montane maquis in New Caledonia: two new species of Pancheria (Cunoniaceae) from the Roche Ouaïème[END_REF][START_REF] Munzinger | A second species in the endemic New Caledonian genus Gastrolepis (Stemonuraceae) and its implications for the conservation status of high-altitude maquis vegetation: coherent application of the IUCN Red List criteria is urgently needed in New Caledonia[END_REF], those are still dense and largely shrubby and do not display distinctive vegetative forms such as large rosette and cushion plants.

It has long been recognized that a striking ecological feature of New Caledonia is the diversity of its soils [START_REF] Jaffré | The relationship between ecological diversity and floristic diversity in New Caledonia[END_REF] and this could have been a major driver for plant diversification (Pillon et al., 2009a,b). However this might have been translated into physiological diversity more than morphological attributes and hence a rather cryptic mode of adaptive radiation (e.g. [START_REF] Pillon | Cryptic adaptive radiation in tropical forest trees in New Caledonia[END_REF].

Finally, New Caledonia also displays few dramatic examples of plant-pollinator coevolution that could compare to, for example, Hawaiian lobeliads and Hawaiian honeycreepers (Carlquist, 1965: 131). There is an interesting case of mutualism reported between the large genus Phyllanthus and Epicephala moths (Kawakita & Kato, 2004), but it did not result in spectacular variations in flower morphology. Pollination syndromes have not been thoroughly investigated in New Caledonia (but see [START_REF] Carpenter | Reproductive traits of tropical rain-forest trees in New Caledonia[END_REF]Kato & Kawakita, 2004;[START_REF] Donovan | Flower-visiting records of the native bees of New Caledonia[END_REF]Hopkins et al., 2015b) and some patterns might have been overlooked. It is possible that the pollination guild of New Caledonia is more depauperate than elsewhere [START_REF] Carpenter | Reproductive traits of tropical rain-forest trees in New Caledonia[END_REF][START_REF] Pauly | Contribution à la connaissance des Hyménoptères Apoidea de Nouvelle-Calédonie et de leurs relations avec la flore butinée[END_REF]. Also, most of the lineages in which zygomorphic flowers are found are under-represented in the flora of New Caledonia: monocots, Asterales, Fabales and Lamiales [START_REF] Pillon | Ultramafic soils and species sorting in the flora of New Caledonia[END_REF], and this may have reduced the opportunities for specific plant-pollinator interactions.

CONCLUSIONS

New Caledonia may have a total of between 62 and 91 endemic genera. Many of these genera have still not been included in molecular phylogenetic studies and the delimitation of others needs further work, and some other genera may be revealed in the future. This number of endemic genera is far greater than in any other Pacific archipelago. Endemic genera may be the result of extinctions outside the island, evolutionary changes on the island or both. In the case of New Caledonia, the first phenomenon may have been the preponderant force. The relative ancient age of the island, a putative climatic stability and a possible protective role of ultramafic substrate against new colonizers may have been key factors in the accumulation of relict lineages. In contrast, evidence for adaptive radiations is limited and this may be linked to the modest contribution of primarily herbaceous lineages to the composition of flora or the limited ecological contrasts on the island beside the diversity of soils. Beyond the now famous Amborella, New Caledonia hosts a large number of unique relicts of conservation significance, as can be expected in old, climatically buffered, infertile landscapes (OCBILs, [START_REF] Hopper | OCBIL theory: towards an integrated understanding of the evolution, ecology and conservation of biodiversity on old-climatically buffered, infertile landscapes[END_REF][START_REF] Hopper | Biodiversity hotspots and OCBIL theory[END_REF]. Endemic genera may be in some cases the sole survivor of ancient lineages and the age and phylogenetic diversity of these taxa will be discussed in a forthcoming paper. It can be anticipated that this will magnify the conservation significance of the ultramafic substrates of New Caledonia, which host most endemic genera and where the preservation of the native ecosystems is most conflicted [START_REF] Pascal | Mining and other threats to the New Caledonia biodiversity hotspots[END_REF]. Updated conservation assessments for these unique lineages are urgently needed to set conservation priorities and preserve these unique branches of the tree of life.

  were all once placed in Kermadecia and further evidence for their reciprocal monophyly is desirable. Virotia L.A.S.Johnson & B.G.Briggs (2/6) is part of subtribe Virotiinae (Mast et al., 2008) with Athertonia L.A.S.Johnson & B.G.Briggs (Queensland) and Helicopsis Sleumer (Indo-Malesia); their relationships are unresolved. Garnieria Brongn. & Gris (monotypic) is nested in the larger Australian genus Persoonia Michx. with the New Zealand endemic Toronia L.A.S.Johnson & B.G.Briggs and the south-western Australian Acidonia L.A.S.Johnson & B.G.Briggs (Weston & Porter, unpub. data, cited in Weston & Barker, 2006). ROSIDS FABALES Fabaceae Egan et al. (2016) found that Arthroclianthus Baill. (2/19) and Nephrodesmus Schindl. (2/5) were sister groups and reciprocally monophyletic in tribe Desmodieae. Polygalaceae Balgoya Morat & Meijden (monotypic) is generally placed in tribe Moutabeae and the study of Persson (2001), which included only a short trnL sequence for this genus, failed to resolve its phylogenetic position in the family or to confirm its placement in this tribe. ROSALES Rhamnaceae The recently described Jaffrea H.C.Hopkins & Pillon (2/2, Hopkins et al., 2015a) is sister to Emmenosperma F.Muell. (occurring in Malesia, Australia, New Caledonia and Fiji).

  Baker f. (3/6) occupies an unresolved position between several multigeneric clades. Menepetalum Loes. (2/4) is sister to Dinghoua R.H.Archer from Queensland and Dicarpellum (Loes.) A.C.Sm.

  , Kanakomyrtus N.Snow (3/6, tribe Myrteae) is polyphyletic with its species mixed with those of the genera Rhodomyrtus (DC.) Rchb. (South-east Asia and Pacific), Pilidiostigma Burret (Australasia) and Octamyrtus Diels (Malesia). The monotypic Myrtastrum Burret is part of the "Australasian group" of Myrteae and is the earliest diverging lineage in this clade (T.N.C. Vasconcelos, pers. comm.). Arillastrum Pancher ex Baill. (monotypic) is well supported as sister to Corymbia K.D.Hill & L.A.S.Johnson + Angophora Cav. in Eucalypteae (Australasia)

  Cupania group, Gongrodiscus and Storthocalyx were inferred as closely related together with one species of the polyphyletic genus Sarcotoechia Radlk. from Australia; however, this relationship has to be clarified by sampling more DNA regions. Podonephelium belongs to another clade in the Cupania group and is sister to the widely distributed genus Alectryon Gaertn. (Malesia, Australia, New Caledonia, New Zealand and Hawaii). In the Dodonaea group, the monotypic Loxodiscus is supported as sister to a clade comprising Harpullia Roxb. (India, south-eastern China, Malesia to Australia, New Caledonia and Pacific Islands), Cossinia Comm. ex Lam. (Mascarenes, New Caledonia, eastern Australia, Fiji), Diplopeltis Endl. (north-western Australia) and Dodonaea (mainly in Australia, Malesia, New Guinea, Carribean and Madagascar). Rutaceae Appelhans et al. (2014) found that Comptonella Baker f. (4/8), Dutaillyea Baill. (1/2) and Picrella Baill. (2/3) were nested in the larger and more widespread Melicope J.R.Forst. & G.Forst. (South-east Asia and Pacific), being close to the New Caledonian members of this genus. The authors suggested that Dutailliopsis T.G.Hartley (monotypic) may also be nested in Melicope, although it has not been included in any molecular phylogenetic studies.

  T.G.Hartley (1/2) has been recovered with strong support as sister to the Australian Acradenia Kippist (both species included). The relationship between Myrtopsis O.Hoffm. (2/8) and a number of Australian genera placed in tribe Boronieae, some of medium size [Leionema (F.Muell.) Paul G.Wilson, Phebalium Vent., Philotheca Rudge], are unresolved. Neoschmidia T.G.Hartley (1/2) is recovered as sister to a diverse clade of Australasian genera including Halfordia F.Muell. and Myrtopsis (Bayly et al., 2013). MALVALES Malvaceae In a phylogenetic study including all the genera of subfamily Sterculioideae, Wilkie et al. (2006) recovered Acropogon Schltr. (2/25) as a member of the moderately supported Brachychiton Schott & Endl. clade. The relationships between Acropogon, Brachychiton (Australia-New Guinea), Argyrodendron (Endl.) Klotzsch (Australia) and Franciscodendron B.Hyland & Steenis (Australia) are unresolved. In a phylogenetic study including all eight genera of tribe Lasiopetaleae (Whitlock et al., 2011), Maxwellia Baill. (monotypic) formed a strongly supported clade with Hannafordia F.Muell. (Australia) and a group of four genera (Thomasia J.Gay, Lysiosepalum F.Muell., Lysiopetalum K.Schum., Guichenotia J.Gay; all Australian), but their exact relationships are unresolved. Thymelaeaceae The phylogenetic relationships of Deltaria Steenis (monotypic) and Solmsia Baill. (1/2) with the genera Lethedon Spreng. (New Caledonia, Australia), Gonystylus Teijsm. & Binn. (Southeast Asia) and Arnhemia Airy Shaw (Australia) in subfamily Gonystyloideae are unresolved

Myodocarpacae

  Myodocarpaceae have a centre of diversity in New Caledonia and include only two genera, which are reciprocally monophyletic[START_REF] Nicolas | The demise of subfamily Hydrocotyloideae (Apiaceae) and the re-alignment of its genera across the entire order Apiales[END_REF]: the endemic New Caledonian Myodocarpus Brongn. & Gris (4/10) and Delarbrea Vieill. (Malesia to New Caledonia). Apiaceae In a phylogenetic study including 40 of the 42 genera previously placed in subfamily Hydrocotyloideae, Nicolas & Plunkett (2009) found that Apiopetalum Baill. (2/2) was sister to Actinotus Labill. (Australasian) in the newly circumscribed subfamily Mackinlayoideae. DISCUSSION How many endemic genera of vascular plants occur in New Caledonia?

:

  Amaroria A.Gray (Simaroubaceae), Degeneria I.W.Bailey & A.C.Sm. (Degeneriacae), Gillespiea A.C.Sm., Hedstromia A.C.Sm., Squamellaria Becc., Sukunia A.C.Sm. (Rubiaceae) and Pimia Seem. (Malvaceae). Amaroria

  listed five endemic genera in this region: Allowoodsonia Markgr. (Apocynaceae), Cassidispermum Hemsl. (Sapotaceae), Kajewskiella Merr. & L.M.Perry (Rubiaceae), Rehderophoenix Burret and Strongylocaryum Burret (Arecaceae).

  cited only a few examples of adaptive radiations in New Caledonia: Araucaria, Dacrydium Lamb, Podocarpus L'Hér. ex Pers. (all relatively small radiations of conifers), Phyllanthus L. (multiple colonization events,

  There are currently only four to six pairs of sister endemic genera: Clematepistephium & Eriaxis, Clinosperma & Cyphokentia, Amphorogyne & Daenikera, Arthroclianthus & Nephrodesmus and, possibly, Morierina & Thiollierea and Kermadecia & Sleumerodendron. There is no clade of three or more endemic genera (but see Pycnandra below).

Monimiaceae

  Renner et al. (2010) recovered the monotypic Kibaropsis Vieill. ex Jérémie in clade III, which also includes the Oceanian Levieria Becc. and Hedycarya J.R.Forst. & G.Forst. Support in this clade is moderate, but Hedycarya appears polyphyletic, with Kibaropsis and Leviera nested inside it. Kibaropsis seems closer to the New Zealand H. arborea J.R.Forst. & G.Forst. (bootstrap 65%) rather than the New Caledonian H. cupulata Baill. Generic delimitation in this group requires further investigations.

  , including all of the species of Areceae, confirmed that the two genera are Burretiokentia, whereas two other Cyphophoenix spp, form a clade sister to the Melanesian genus Physokentia Becc. This study also indicates that three Basselinia spp. and the Lord Howe Island endemic Hedyscepe H.Wendl. & Drude form a polytomy, although

	(2/2), Chambeyronia Vieill. (2/2) and Kentiopsis Brongn. (4/4), the Australian
	Archontophoenix H.Wendl. & Drude, and the Papuan Actinorhytis H.Wendl. & Drude, but
	relationships and generic delimitations between the three New Caledonian genera and
	Archontophoenix remain unclear, including the monophyly of Chambeyronia and Kentiopsis
	(Domenech et al., 2014). Basselinia Vieill. (3/14), Burretiokentia Pic.Serm. (2/5) and
	Cyphophoenix H.Wendl. ex Benth. & Hook.f (3/4) are placed in subtribe Basseliniinae. The
	phylogenetic study by Baker et al. (2011) suggested that Cyphophoenix nucele H.E.Moore
	could be sister to Hedyscepe has been assigned to a different subtribe, Rhopalostylidinae. Further work is
	needed to clarify the taxonomic circumscriptions of the genera in subtribes
	Archontophoenicinae and Basseliniinae.
	reciprocally monophyletic. Subtribe Archontophoenicinae include Actinokentia Dammer

ACKNOWLEDGEMENTS

We thank Bill Baker, Mark Chase, Ashley Egan, Hervé Jourdan, Eve Lucas, Jean-Yves Meyer, Arnaud Mouly, Laurence Ramon, Tim Utteridge, Hervé Vandrot and Thais Vasconcelos for comments or for sharing unpublished results with us, Vanessa Hequet for providing a picture of Loxodiscus, and Carlos García-Verdugo, Phil Garnock-Jones and an anonymous reviewer for insightful reviews on a previous version of this manuscript.