Disentangling the diversity and taxonomy of Hymenophyllaceae (Hymenophyllales, Polypodiidae) in the Mascarene archipelago, with ecological implications

We here explore the diversity and ecology, and update the taxonomy of the fern family Hymenophyllaceae, which forms one of the most diverse and emblematic fern assemblages in rainforests of the Mascarene archipelago in western Indian Ocean. Since 1999, we extracted data from floras, literature, and field investigations conducted, and from an exhaustive examination of the collections at P, REU, and MAU. Our checklist recognizes 26 taxa involving 23 species, 2 local varieties and 1 new forma. We reconsider area of distribution in Mascarene Hymenophyllaceae and at least 3 species appear to be restricted to the archipelago. We discuss the updated taxonomy and discrimination of each taxon (including a new nomenclatural proposition for Hymenophyllum tenellum here renamed as H. fumarioides) and provide a dichotomous key. We present and discuss the ecology and elevational distribution of each species, in addition to the local endemicity. Finally, we emphasize the importance of threatened lowland rainforests and of wet ravines in semi-dry forests, which host a high level of diversity in the context of local conservation of habitats.