Cryptic speciation revealed in Scandinavian Racomitrium lanuginosum (Hedw.) Brid. (Grimmiaceae)

ABSTRACT Introduction. Within Racomitrium Sect. Racomitrium, several species are distinguished in the Southern Hemisphere, but only the variable R. lanuginosum (Hedw.) Brid. exists in the north. Plants deviating from the common R. lanuginosum phenotype in leaf orientation and in almost entire or weakly dentate hair-point margins suggest that more than one species may exist in this region. Methods. Sixty-five specimens of R. lanuginosum, including eleven deviating ones (four growing intermixed with ‘normal’ plants), and two of each of the Southern Hemisphere R. geronticum Müll.Hal. and R. pruinosum (Wilson) Müll.Hal. were studied, based on the nuclear ITS and the plastid rpl16 and trnG. Relationships among specimens were explored with NeighborNet split networks, maximum parsimony, and Jacknife analyses. Key results. The molecular analyses revealed one grade and four distinct lineages, two of which correspond with the Southern Hemisphere species. Two of the three R. lanuginosum entities are widespread in Scandinavia, whereas the third occurs only in the mountains. Morphologically deviating plants do not form their own lineage but appeared in all three R. lanuginosum entities. Conclusions. The three entities within R. lanuginosum do not form a monophyletic group, good support exists for their recognition, and they are molecularly as distinct as the two morphologically recognisable Southern Hemisphere species. They should therefore be recognised as cryptic species. The morphologically deviating plants represent genotypic differentiation, which was further confirmed by molecular evidence in three out of four occurrences where they grew intermixed with ‘normal’ plants. Since deviating plants occur in all three cryptic species they should not be taxonomically recognised.