Lumping or splitting? The case of Racomitrium (Bryophytina: Grimmiaceae)

Abstract

The genus Racomitrium (Grimmiaceae: Racomitrioideae) was recently segregated into four genera-Racomitrium, Niphotrichum, Codriophorus, and Bucklandiella-following an infrageneric division originally proposed more than 100 years ago based on morphological traits such as the presence and shape of laminal cell papillae and hyaline leaf hairpoints, and differences in peristome teeth morphology and costa structure. Here we present a molecular phylogeny of Racomitrium s.l. based on nuclear ITS and plastid rps4-trnL and trnK/matK-psbA sequences, to test the monophyly of these four morphological entities. Our results solely support the monophyly of Racomitrium s.str., which includes only R. geronticum, R. lanuginosum, and R. pruinosum, while the members of the other segregate genera are distributed in different clades, rendering them polyphyletic (Bucklandiella, Codriophorus) or paraphyletic (Niphotrichum). Ancestral state reconstruction shows high levels of homoplasy in the characters usually used for the infrageneric division of Racomitrium s.l. (i.e., leaf papillae shape, perichaetial leaves morphology). Based on this evidence, we propose a return to a broader concept of Racomitrium, and adopt a revised sectional classification. Therefore, we propose new combinations for some recently described species of Bucklandiella and Codriophorus.