New insights into the diversity, taxonomy and history of the fern genus Trichomanes (Hymenophyllaceae, Polypodiidae), with a focus on Africa and the western Indian Ocean
Résumé
The filmy fern genus Trichomanes mainly comprises Neotropical species and a few taxa in Africa and the western Indian Ocean. The aim of this study is to infer the phylogenetic placement of all five Afro-Malagasy taxa in the genus and to investigate their history via an expanded and dated phylogenetic analysis including 39 species representing over half the diversity of the genus. The results support the monophyly of Trichomanes including all the sampled species attributed to the genus, but also suggest the inclusion of the species Abrodictyum cellulosum, revealing a morphological diversity of the genus greater than what was traditionally recognized, and highlighting the importance of the campanulate sorus as a generic diagnostic character. To accommodate those new phylogenetic results and morphological investigations, we describe a new subgenus Afrotrichomanes grouping the Afro-Malagasy taxa (except T. crenatum). The dated history of the genus among the trichomanoids suggests at least two origins for the Palaeotropical species. A recent Cainozoic colonization from the Neotropics towards Africa gave rise to the West African taxon T. crenatum, and a possible Mesozoic vicariance event gave rise to subgenus Afrotrichomanes. The low species diversity of the genus in the Afro-Malagasy region is discussed.