Partial generic revision of Barbula (Musci: Pottiaceae): Re–establishment of Hydrogonium and Streblotrichum, and the new genus Gymnobarbula

Abstract Large genera, that were defined using a restricted suite of morphological characters, are particularly prone to be polyphyletic. We analysed a representative selection of species traditionally assigned to the genus Barbula, believed to represent the largest genus of the moss family Pottiaceae, but which recently was suggested to be polyphyletic. Special attention was paid to species traditionally assigned to Barbula sect. Hydrogonium and sect. Convolutae, in which phylogenetic relationships are likely to be incongruent with morphological traits, which could have evolved in adaptation to hydric and otherwise extreme habitats. Our phylogenetic analysis was based on nrITS and chloroplast rps4 and trnM–trnV sequence data and resolved only the type of the genus, B. unguiculata, plus B. orizabensis, in subfamily Pottioideae, while most of the species occurring in the Northern Hemisphere are part of Trichostomoideae and need to be recognized within the re–established and partly re–defined genera Hydrogonium and Streblotrichum. The phylogenetically and morphologically divergent B. bicolor needs to be removed from Streblotrichum to a newly described genus, Gymnobarbula. Numerous taxonomic changes and nomenclatural novelties, resulting from the molecular, morphological and nomenclatural studies are proposed for taxa of Hydrogonium, particularly within the H. consanguineum clade. Lectotypes are selected for Tortula angustifolia Hook. & Grev. (≡ Hydrogonium angustifolium (≡ Hook. & Grev.) Jan Kučera, comb. nov.), Tortula consanguinea Thwaites & Mitt. (≡ Hydrogonium consanguineum (Thwaites & Mitt.) Hilp.) and Tortula flavescens Hook. & Grev. (= Hydrogonium consanguineum (Thwaites & Mitt.) Hilp.).