Hidden diversity in the Trichostomum brachydontium complex (Pottiaceae, Bryophyta) revealed by integrative taxonomy

We applied an integrative taxonomic approach combining multilocus phylogenetics, morphoanatomical analyses, and multivariate statistics to reassess the diversity of the Trichostomum brachydontium complex in South America. Analyses of five molecular markers (ITS, atpB-rbcL, trnG, trnL-F, rps4) and 67 morphological characters revealed that specimens traditionally identified as T. brachydontium represent 11 distinct lineages, none matching the diagnostic traits of T. brachydontium sensu stricto. Accordingly, T. brachydontium is excluded from the South American flora. Ten lineages exhibit significant phenotypic differentiation supported by PCA, LDA (accuracy = 96.6%), and hierarchical clustering. Until further studies, four of them are recognized as T. antillarum, T. basilatinervium, T. hondurense and T. termitarum. Our results highlight cryptic speciation and biogeographic divergence between European and South American populations, underscoring the need for taxonomic revision. Additionally, phylogenetic analyses confirm the placement of T. involutum within the genus Trichostomum. We propose a new combination: Neotrichostomum jamaicense (Mitt.) M.J. Cano, M.T. Gallego & Omar Rodr., comb. nov. The known distribution of Trichostomum antillarum is here substantially expanded across South America, T. hondurense is newly recorded in South America, and T. termitarum is reported from Argentina for the first time.