A multilocus phylogeny of the moss genus Didymodon and allied genera (Pottiaceae): generic delimitations and their implications for systematics

Abstract

Didymodon s.l. is one of the largest genera in the moss family Pottiaceae, with about 122 species distributed in all continents. This, together with its high degree of morphological variation, has made it one of the taxonomically most challenging genera of Pottiaceae. Circumscription of Didymodon s.l. has been, and still is, controversial. To date, the only molecular study that has investigated the delimitation of the genus has been far from comprehensive (35 samples from 27 species), limited in geographical scope (mainly restricted to Europe), and based exclusively on ITS sequences. To evaluate the circumscription of Didymodon s.l. and its relationships with the allied genera Andinella, Gertrudiella, and Tridontium, we conducted phylogenetic analyses of DNA sequences for three plastid markers (atpB–rbcL, trnG, and trnL‐F) and one nuclear locus (ITS) for 335 samples representing 86 species of Didymodon s.l. (ca. 70%), and all taxa of the genera Andinella, Gertrudiella, and Tridontium. Individual markers and concatenated matrices were analyzed using maximum likelihood and Bayesian approaches. Our results indicate that Didymodon s.l. is not monophyletic, because Andinella, Gertrudiella, and Tridontium species are nested within it. Species of these four genera can be divided into eight well‐supported and morphologically distinct genera: Didymodon s.s., Geheebia, Gertrudiella, Husnotiella, Trichostomopsis, Tridontium, Vinealobryum, and Zanderella. In correspondence with the results presented, 38 new combinations, 10 new synonyms, and a new name are provided for those taxa where required, and lectotypes are designated for 13 names. A diagnostic key to the eight recognized genera is provided.