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The New Caledonian biodiversity hotspot contains many micro-hotspots that exhibit high plant micro-endemism, and that are facing different types and intensities of threats. The Belep archipelago, and especially Île Art, with 24 and 21 respective narrowly endemic species (1 Extinct, 21 Critically Endangered and 2 Endangered), should be considered as the most sensitive micro-hotspot of plant diversity in New Caledonia because of the high anthropogenic threat of fire. Nano-hotspots could also be defined for the low forest remnants of the southern and northern plateaus of Île Art. With an average rate of more than one new species described for New Caledonia each month since January 2000 and five new endemics for the Belep archipelago since 2009, the state of knowledge of the flora is steadily improving. The present account of eight new species from Île Art (Bocquillonia montrouzieri Gâteblé & McPherson, Cleidion artense Gâteblé & McPherson, Endiandra artensis Munzinger & McPherson, Eugenia belepiana J.W.Dawson ex N.Snow, Eugenia insulartensis J.W.Dawson ex N.Snow, Macaranga latebrosa Gâteblé & McPherson, Planchonella serpentinicola Swenson & Munzinger and Psychotria neodouarrei Barrabé & A.Martini) further demonstrates the need both to recognise the Belep Islands as a major New Caledonian micro-hotspot and to formulate concrete conservation programs for the archipelago.
Background and Aims Recent parsimony-based reconstructions suggest that seeds of early angiosperms had either morphophysiological or physiological dormancy, with the former considered as more probable. The aim of this study was to determine the class of seed dormancy present in Amborella trichopoda, the sole living representative of the most basal angiosperm lineage Amborellales, with a view to resolving fully the class of dormancy present at the base of the angiosperm clade.Methods Drupes of A. trichopoda without fleshy parts were germinated and dissected to observe their structure and embryo growth. Pre-treatments including acid scarification, gibberellin treatment and seed excision were tested to determine their influence on dormancy breakage and germination. Character-state mapping by maximum parsimony, incorporating data from the present work and published sources, was then used to determine the likely class of dormancy present in early angiosperms.Key Results Germination in A. trichopoda requires a warm stratification period of at least approx. 90 d, which is followed by endosperm swelling, causing the water-permeable pericarp-mesocarp envelope to split open. The embryo then grows rapidly within the seed, to radicle emergence some 17 d later and cotyledon emergence after an additional 24 d. Gibberellin treatment, acid scarification and excision of seeds from the surrounding drupe tissues all promoted germination by shortening the initial phase of dormancy, prior to embryo growth.Conclusions Seeds of A. trichopoda have non-deep simple morphophysiological dormancy, in which mechanical resistance of the pericarp-mesocarp envelope plays a key role in the initial physiological phase. Maximum parsimony analyses, including data obtained in the present work, indicate that morphophysiological dormancy is likely to be a pleisiomorphic trait in flowering plants. The significance of this conclusion for studies of early angiosperm evolution is discussed.
Background and Aims This work aimed to gain insight into the breeding system at the base of living angiosperms through both character state reconstructions and the study of sex ratios and phenotypes in the likely sister to all other living angiosperms, Amborella trichopoda.Methods Sex phenotypes were mapped onto a phylogeny of basally diverging angiosperms using maximum parsimony. In parallel, sex ratios and phenotypes were studied over two consecutive flowering seasons in an ex situ population of A. trichopoda, while the sex ratio of an in situ population was also assessed.Key Results Parsimony analyses failed to resolve the breeding system present at the base of living angiosperms, but indicated the importance of A. trichopoda for the future elucidation of this question. The ex situ A. trichopoda population studied showed a primary sex ratio close to 1:1, though sex ratio bias was found in the in situ population studied. Instances of sexual instability were quantified in both populations.Conclusions Sex ratio data support the presence of genetic sex determination in A. trichopoda, whose further elucidation may guide inferences on the breeding system at the base of living angiosperms. Sexual instability in A. trichopoda suggests the operation of epigenetic mechanisms, and the evolution of dioecy via a gynodioecious intermediate.
Oxera is a genus of c. 20 species from New Caledonia and Vanuatu. Its phylogenetic placement in Lamiaceae (Ajugoideae) remained uncertain until studies showed close affinities with the large pantropical genus Clerodendrum, the Indo-Pacific Faradaya (three species) and the monotypic Hosea from Borneo. We reassessed the relationships of Oxera with these genera by building a phylogenetic framework based on six plastid and six nuclear loci and on a sampling including 30 ingroup species. The results show that Clerodendrum and its closely related genera are sister to the alliance encompassing Faradaya, Hosea and Oxera. Hosea is sister to all species of Oxera and Faradaya. Faradaya is recovered as polyphyletic as it is partly nested within Oxera. Extensive morphological variability is observed in Oxera. However, Oxera also shares strong similarities with the three Faradaya species. Polyphyletic Faradaya is therefore placed in synonymy with Oxera and we propose three new combinations: O. amicorum, O. lehuntei and O. splendida. A unique synapomorphy supports this new circumscription of Oxera: the petiole vascularization consisting of several small vascular bundles arranged in an interrupted full circle (vs. a large bundle in a half circle in other ajugoids). Oxera thus comprises c. 37 species, with a diversity centre in New Caledonia. Biogeographical processes, plastid paralogy and vascularization shift are discussed.
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