A phylogenetic revision of the genus Hypnum: Towards completion

Abstract

AbstractThe taxonomy of pleurocarpous mosses has long been based on a few key characters such as the presence or absence of a single costa or the posture of the leaves. Molecular analyses performed in the past two decades have often challenged the traditional familial and generic delimitations, as these simple characters have evolved repeatedly. For nearly a century the genus Hypnum has been defined principally by the combination of falcate leaves with a short double costa, differentiated alar cells and the mostly procumbent growth form. Although several earlier treatments revealed the polyphyly of Hypnum in its traditional sense, none of them included a representative selection of the species on a worldwide basis. Therefore, we sampled most of the taxa that were attributed to the genus by the monographer H. Ando, and performed a molecular phylogenetic analysis using DNA sequence data from two chloroplast loci and the nuclear ribosomal ITS region. The outcome of this analysis was a revision of the phylogenetic affinities of these representative taxa; we also matched more than 15 molecularly defined lineages of Hypnum s.l. to morphological characters and solved several nomenclatural problems. Consequently, we suggest taxonomic and nomenclatural re‐arrangements, which encompass the vast majority of taxa attributed to Hypnum and do not contradict their known molecular affinities. We deliver additional support for some of the most recent delimitations of Hypnum s.l. but introduce new data to refute the proposals for the segregation of the genera Lignocariosa and Insomniella, which can be accommodated in the existing genera Pseudohygrohypnum and Calohypnum, respectively. Similarly, we dispute the inclusion of Hypnum sauteri in Anacamptodon and propose the establishment of a new genus for this species. Instead of placing Callicladium in the Hypnaceae and Jochenia in the Entodontaceae, respectively, we propose new families for these two genera. Finally, we propose three other new genera to accommodate (1) Hypnum circinale, (2) H. chrysogaster with H. subchrysogaster, and (3) H. dieckii, respectively. The main diagnostic features of Hypnum in earlier treatments are shown to represent broadly distributed homoplastic characters, correlated with adaptation to the habitat conditions, such as the moisture content.