A molecular and morphological study of Leucobryum in Britain and Europe: the presence of L. albidum (P.Beauv.) Lindb. confirmed

ABSTRACT Introduction. Initial morphometric investigations into the differences between Leucobryum glaucum (Hedw.) Ångstr. and L. juniperoideum (Brid.) Müll.Hal. in Britain showed that some populations could not be clearly assigned to either species. An intensive morphological and molecular study was therefore undertaken to understand the diagnostic characters of the European species of the genus, including L. albidum (Brid. ex P.Beauv.) Lindb., whose reported presence in Europe was surrounded by uncertainty. There has been little agreement among previous authors on the relative taxonomic importance of the different morphological characters, or on their metrics. Methods. Molecular sequencing using nuclear and chloroplast markers, in conjunction with previously accessioned data, allowed judgement of the taxonomic importance of various methods for morphological discrimination. These methods included both existing published techniques and newly discovered diagnostic characters. This integrated process was cyclical, the morphological analysis being directed and confirmed by the sequencing of selected specimens. Results and discussion. Data are presented demonstrating the correlation between molecular identification and certain morphological characters in the three European species of Leucobryum. Leucobryum albidum is confirmed as a locally frequent member of the British flora and it is also shown to be present in Ireland and western part of continental Europe. Leucocyst pore morphology is described and its value as a diagnostic character is discussed. An identification key is provided for the three species. Plants from two sites are shown to have a discordance between nuclear and plastid molecular markers and we consider the possibility that horizontal gene transfer could explain the observed patterns.