Psilotum (Psilotaceae-Ophioglossales): a taxonomic assessment based on morpho-anatomical studies of the species from the Neotropics

The recent discovery of Psilotum x intermedium in Mexico prompted us to reassess the nomenclature of this genus, which has global implications. From an extensive review of nomenclatural types and herbarium specimens, field collections, and a morpho-anatomical analysis, P. nudum and P. flaccidum are treated as accepted species, while P. x complanatum is treated as an interspecific hybrid between them. With this clarification, we specify their main synonymies and designate seven lectotypes (for Bernhardia schiedeana, Psilotum complanatum var. latissimum, P. complanatum var. mexicanum, P. floridanum, P. neocaledonicum, P. triquetrum, P. triquetrum var. gracile) and we select an epitype to give taxonomic support to the hybrid. We provide descriptions, diagnostic comments, and a key for identification of the accepted taxa, and also update the geographical ranges of these three taxa, mainly in Neotropics.