Conflicting molecular and morphological evidence of evolution within the Bryaceae (Bryopsida) and its implications for generic taxonomy

Abstract

Phylogenetic analyses within the Bryaceae were performed based on DNA sequence data from three chloroplast genomic regions. Special emphasis was placed on sampling the small tuber-bearing species of Bryum ('Erythrocarpa') from Europe and those with axillary bulbils (B. dichotomum group). Multiple exemplars were studied for most of the species investigated. As in previous studies, the results demonstrate a pattern of evolutionary diversification that differs widely from that implied by traditional generic and subgeneric classifications. More recent generic arrangements based exclusively on morphological characters are also shown to seriously misrepresent phylogeny because of convergent evolution of morphology. Among the 'Erythrocarpa', for instance, the superficially similar B. rubens and B. subapiculatum emerge as only distant relatives, the former being close to B. capillare (treated in Ptychostomum here) whereas the latter is close to B. alpinum (placed in Imbribryum here). Likewise, using only morphological characters, B. dunense and B. versicolor [Bryum s.s.] may both be almost indistinguishable from some specimens of B. caespiticium [Ptychostomum]. On the other hand, rapid differentiation of morphology has occurred within some clades, notably of 'Plagiobryum' zieri from within Ptychostomum. Thus the argument is reiterated that 'classification of the Bryaceae based on morphological characters alone cannot be defended', since it leads to classifications which are incongruent with phylogeny and do not take account of all available information. Hence a generic classification is proposed here containing mainly those Bryaceae for which molecular data are available. Several nomenclatural questions that arise from this are resolved.