The main diversity among genus '' Araucaria'' is hosted in New Caledonia, where 14 species, all endemic, are described out of a total of 20 extant species.Mill RR., Ruhsam M., Thomas PI., Gardner MF. and Hollingsworth PM. 2017. ''Araucaria goroensis'' (Araucariaceae), a new Monkey Puzzle from New Caledonia, and nomenclatural notes on ''Araucaria muelleri''. ''Edinburgh Journal of Botany'' 1–17. These New Caledonian species are mainly found as dispersed populations in open areas, where competition is less intense.Veillon JM. 1980. Architecture des espèces néo-Calédoniennes du genre ''Araucaria''. ''Candollea'' 35: 609-640. New Caledonia, considered as the smallest of the most significant

biodiversity hotspot A biodiversity hotspot is a biogeographic region with significant levels of biodiversity that is threatened by human habitation. Norman Myers wrote about the concept in two articles in ''The Environmentalist'' in 1988 and 1990, after which the c ...

s in the world, hosts a unique flora of which 75.1% is endemic. Species of ''Araucaria'' trees can be found in every habitat that New Caledonia possesses. However, almost all of them are growing on ultramafic substrate, characterized by low fertility (low N, P, K levels) and high levels of heavy metals (nickel, cobalt, etc.).

Phylogenic history

Context

An alternative to the view that the island is a museum for plant relicts is the possibility that the diversity results from a recent radiation, subsequent to the island's emergence.Kranitz ML, Biffin E, Clark A, Hollingsworth ML, Ruhsam M, Gardner MF, ''et al.'' 2014. Evolutionary Diversification of New Caledonian ''Araucaria''. PLoS ONE 9(10) New Caledonia was part of the supercontinent Gondwana, and separated from Australia 80 Ma. However, geological evidence suggests that New Caledonia was submerged during

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

(ca. 65 Ma) and

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

(until ca. 37 Ma). The actual New Caledonian biota may then result from a total recolonization since the Oligocene. Araucaria columnaris Prony 2

The first ''Araucaria'' species were mentioned by Guillaumin in 1948: ''A. balansae'', ''A. cookie'', '' A. montana'', '' A. muelleri'' and '' A. rulei''. In 1949, J. T. Bucholz added three new species: '' A. bernieri'', '' A. biramuluta'' and '' A. humboldtensis''. In 1972, D. J. de Laubenfels described five other species: '' A. luxurians'', separated from ''A. cookie'' renamed '' A. columnaris'', '' A. laubenfelsii'', '' A. nemorosa'', '' A. scopulorum'' and '' A. schmidii'', and divided these thirteen species in two groups. The first includes species following the Massart model (plagiotropic branches, partial reiterations) while the second includes species following the Rauh model (orthotropic branches and no reiterations) with bigger leaves. Veillon described how the morphology of New Caledonian ''Araucaria'' conforms to these models and noticed that species following the Rauh model have bigger leaves. He also designed a key to help in field identification, based on characters fixed in adults, so ecological factors impacting tree morphology won't interfere with identification. New Caledonian ''Araucaria'' species belong to the ''Eutacta'' section, one of the four sections defined by Wilde and Eames in 1952.Wilde MH, AJ Eames. 1952. The ovule and “seed” of ''Araucaria bidwillii'' with discussion of the taxonomy of the genus. II. Taxonomy. ''Ann Bot'' 16: 27-47. This section also includes '' A. heterophylla'' from Norfolk Island, and '' A. cunninghamii'' hosted by both Australia and New Guinea.

Rejection of the Gondwanan hypothesis

In 1998, first genetic analyses based on ''RBCL'' gene sequence validated the recognition of the four sections within genus ''Araucaria''.Setoguchi H., Osawa T.A., Pintaud J.-C., Jaffré T., and Veillon J-M. 1998. Phylogenetic relationships within Araucariaceae based on rbcL gene sequences. ''Am. J. Bot.'' 85: 1507-1516. Among ''Eutacta'' section, New Caledonian species formed a monophyletic group where ''A. cunninghamii'' (Papua New Guinea) was derived first, then ''A. heterophylla'' (Norfolk Island). The New Caledonian species revealed a strong homology for ''rcbL'' sequences (from 99.5 to 100%), where 10 out of 13 species are identical for this gene sequence. This strong homology and ''A. heterophylla'' as a sister group of New Caledonian species (the Norfolk Island being relatively young, less than 3 million years old) are first elements suggesting a recent differentiation of ''Araucaria'' trees in New Caledonia. This hypothesis comes in opposition of an older Gondwanan origin. Gaudeul ''et al.'' attempted in 2012 to better describe the evolutionary relationships and diversification of New Caledonian species by using AFLP markers and by performing

Bayesian Thomas Bayes (/beɪz/; c. 1701 – 1761) was an English statistician, philosopher, and Presbyterian minister. Bayesian () refers either to a range of concepts and approaches that relate to statistical methods based on Bayes' theorem, or a followe ...

, genetic distances and

cladistics Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...

analyses.Gaudeul M., Rouhan G., Gardner MF. and Hollingsworth PM. 2012. AFLP markers provide insights into the evolutionary relationships and diversification of New Caledonian ''Araucaria'' species (Araucariaceae). ''American Journal of Botany'' 99: 68-81. Ecological, morphological and geographical parameters were also considered in the study, which ended supporting a recent diversification of the genus in New Caledonia. Moreover, another genetic group was created: coastal species. However, no evidence were shown for more environment implication in driving speciation, which may be the result of both adaptation and

allopatry Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

. The concept of cryptic species, rare among such an iconic group, is mentioned, regarding several divergent populations. In the meantime, Escapa and Catalano published a phylogenetic analysis using parsimony. For the first time in the family

Araucariaceae Araucariaceae – also known as araucarians – is an extremely ancient family of coniferous trees. The family achieved its maximum diversity during the Jurassic and Cretaceous periods and the early Cenozoic, when it was distributed almost worldw ...

, genetic (19 plastid, 2 nuclear and 2 mitochondrial genomic regions) and morphologic data (52 discrete and 10 continuous characters) were combined, confirming a strong monophyly for the 4 sections existing. However, relationships among New Caledonian species remain difficult to elucidate even if their relatively recent origin is confirmed by phylogeny based on combination of plastid and nuclear data, and the use of

molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleo ...

. While this study seems to corroborate with overwater dispersal consecutively to the submersion of New Caledonia, New Caledonian ''Araucaria'' species seems too old to originate from one single dispersal from Australia to Norfolk Island, and then to New Caledonia.

Cryptic diversity

The complexity of species identification and delimitation in New Caledonian ''Araucaria'' is illustrated by Rusham ''et al.'' (2016),Ruhsam M., Rai HS., Mathews S., Ross TG., Graham SW., Raubeson LA., Mei W., Thomas P.I., Gardner M.F., Ennos R.A., ''et al.'' 2015. Does complete plastid genome sequencing improve species discrimination and phylogenetic resolution in ''Araucaria''? ''Molecular Ecology Resources'' 15: 1067-1078. underlying a cryptic diversity present between two relative species (''A. rulei'' and ''A. muelleri''). This work leads to the identification of a fourteenth endemic species, ''Araucaria goroensis,'' confirming the difficulty to distinguish species among the Monkey Puzzle genus in the territory. This new species was initially confused with ''A. muelleri'', but it appears to be more closely related to ''A. rulei''. Distinctions with the latter hold in larger leaves, microsporophylls without a shouldered base and shorter female cone bracts. The origin of such a diversity among the genus ''Araucaria'' in New Caledonia still remain unclear, but appears to be relatively recent. Also speciation may be still be processed as suggested by the cryptic diversity observed among the genus. {, class="wikitable" !Group !Species !IUCN status !Leaf length (mm) !Leaf width (mm) !Architectural model !Substrate !Habitat !Altitude (m) , - , Coastal , '' A. columnaris'' , LC , 5-7 , 4-5 , Massart , Calcareous , Calcareous platforms , < 50 , - , , '' A. nemorosa'' , CR , 6-10 , 1.5-3 , Massart , Ultramafic , Maquis , < 100 , - , , '' A. luxurians'' , EN , 5-7 , 4-5 , Massart , Ultramafic , Humid evergreen forest , < 300 , - , Small-leaved , '' A. bernieri'' , VU , 2-3.5 , 1.5-2.5 , Massart , Ultramafic , Humid evergreen forest, deep valleys , 100 - 800 , - , , '' A. schmidii'' , VU , 7-10 , 1.5-2 , Massart , Acidic , Montane cloud forest , > 1400 , - , , '' A. scopulorum'' , EN , 3-4 , 2.5-3 , Massart , Ultramafic , Maquis , 50 - 800 , - , , '' A. subulata'' , NT , 4-6 , 2-2.5 , Massart , Ultramafic , Humid evergreen forest, deep valleys , 100 - 1100 , - , Large-leaved , '' A. biramulata'' , VU , 7-9 , 5-6 , Massart , Ultramafic , Humid evergreen forest, deep valleys , 300 - 1000 , - , , ''A. goroensis'' , EN , 26-33 , 1-16 , Rauh , Ultramafic , Maquis , 150 - 550 , - , , '' A. humboldtensis'' , EN , 5-6 , 4-5 , Massart , Ultramafic , Maquis of high altitude , 600 - 1500 , - , , '' A. laubenfelsii'' , NT , 12-20 , 8-10 , Massart , Ultramafic , Evergreen forest or maquis , 700 - 1200 , - , , '' A. montana'' , VU , 11-14 , 7-8 , Massart , Ultramafic and acidic , Dense humid forest or maquis , 400 - 1200 , - , , '' A. muelleri'' , EN , 30-35 , 15-20 , Rauh , Ultramafic , Dense humid forest or maquis , 150 - 1200 , - , , '' A. rulei'' , EN , 20-25 , 11-14 , Rauh , Ultramafic , Dense humid forest or maquis , 400 - 800

References

External links

www.endemia.nc
Fauna and flora from New Caledonia.
New Caledonian Araucaria Research
Royal Botanic Gardens Edinburgh ''Araucaria'' website. Araucaria Endemic flora of New Caledonia