New circumscription of Trichomanes cupressoides Desvaux (Hymenophyllaceae), an endemic filmy fern from the Seychelles (Indian Ocean), and new insights into the genus Abrodictyum C.Presl in the western Indian Ocean

Abstract

The filmy fern Abrodictyum cupressoides, initially reported from Madagascar and the Seychelles (locus classicus), is often confused in the field and in collections with similar local species, especially the pantropical A. rigidum. A comparative morphological investigation of Malagasy and Seychellois specimens finds strong differences between A. cupressoides and A. rigidum as well as between Malagasy and Seychellois A. cupressoides, suggesting three distinct morpho-species. A molecular phylogeny based on rbcL sequences focused on the genus Abrodictyum shows the polyphyly of both A. cupressoides and A. rigidum, and reveals that A. cupressoides should be excluded from Abrodictyum, would belong to Trichomanes and is restricted to the Seychelles. A new description for Seychellois Trichomanes cupressoides is thus proposed. In addition, generic treatments for Malagasy T. pachyphlebium, T. madagascariense, T. boivinii and African A. guineense are discussed.