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A taxonomic revision of all native Myrtaceae genera (Eugenia and Syzygium) of the Comoros is presented based on herbarium specimens and molecular and palynological evidence. Eight native species are recognised, seven of which are endemic to the archipelago. We describe the following five new native species: Eugenia choungiensis, E. pascaliana, Syzygium comorense, S. labatii, and S. tringiense. Eugenia anjouanensis is reduced to synonymy under E. comorensis. Lobed stigmas are reported for the first time in Eugenia and only the second time in Myrtaceae. Androdioecy is reported in Eugenia for the first time outside of continental Africa, and its reproductive system is discussed in light of our findings. Preliminary conservation assessments for each native species are calculated according to IUCN Red List criteria, with the majority being threatened with extinction. Recent fieldwork coupled with widespread habitat conversion in the vicinity of the only known specimen suggests strongly that S. humblotii is now extinct.

Two new species endemic to Mayotte are described and illustrated : Marsdenia mayottae W.D. Stevens, Labat & Barthelat and Tylophora mayottae W.D. Stevens, Labat & Barthelat (Apocynaceae, Asclepiadoideae). Marsdenia mayottae is similar to Marsdenia vohiborensis Choux from Madagascar but differs by its very small or sometimes absent corona. Tylophora mayottae is morphologically close to Tylophora coriacea Marais but differs by its much smaller flowers. These two new species, discovered in during recent inventories, are assessed as threaten following the Categories and the Criteria of the IUCN Red List.

In this study, we used an integrative approach combining morphological and molecular data with ecology, in order to clarify the identity of a Dombeya newly recorded as occurring in Mayotte. Morphological and molecular evidence are in agreement and convincingly show that specimens of this newly recorded species can be confidently assigned to D. rosacea, previously known only from four herbarium sheets from Madagascar. The new populations of this species in the Comoros significantly expand the extant area of occupancy of D. rosacea. Ecological preferences are also discussed, as populations of D. rosacea were found in greatly contrasting sub-humid habitats. This newly reported geographical disjunction between the Comoros and Madagascar strengthens the evidence for a biogeographic connection between the floras of these two regions.

Threatened flora of Mayotte : heritage value and challenges for conservation. — This paper deals with the natural history and the flora of Mayotte by presenting some of its characteristics and providing an assessment of its conservation status. Mayotte is a French islands group belonging to the Comoros archipelago (Indian Ocean), located between Madagascar and East Africa. Its geological history, its geographical position and multiple human influences have shaped some remarkable landscapes composed by unique ecosystems and habitats, with an extraordinary biodiversity for a small territory. Since the first inhabitants, via the colonial centuries to the contemporary era, natural vegetation is restricted to the bare minimum but nevertheless it houses most of the plant biodiversity in Mayotte. As sanctuaries these small natural areas are unfortunately still poorly known and highly threatened. The flora of Mayotte was not well studied in the past because the naturalists’ attention was probably drawn by Madagascar. Most of the discoveries were made during the two main periods of investigation that took place during the second half of the nineteenth century and the late twentieth to date. The vascular flora of Mayotte is composed by 681 species that have been recently evaluated by using the categories and criteria of the IUCN Red List. To illustrate the need and urgency to ensure the conservation of this unique heritage, a “Top fourteen” of the critically endangered species is proposed and suggestions for conservation measures are discussed.