Molecular markers reveal cryptic species within <i>Polytrichum commune</i> (common hair-cap moss)

Based on morphological characters only, the taxonomy of the moss genus Polytrichum has still not been fully resolved. Application of molecular techniques might clarify some of these problems. Within P. commune s.l., the taxonomic status of several varieties, e.g., P. commune var. commune and P. commune var. uliginosum, is still debated. This study uses allozyme electrophoresis to show that there are two distinct allozyme multi-locus genotypes within our P. commune samples. These two multi-locus genotypes coincide with both differences in morphology and differences in habitat association. This division is corroborated by observations from different Danish and Dutch populations. Based on these results, in connection with a genetic comparison of the two infraspecific taxa of P. commune s.l. with a related species P. formosum, we argue that P. commune var. commune and P. commune var. uliginosum are two genetically distinct entities with fixed morphological differences and a considerable niche differentiation. They should, therefore, be regarded as two distinct species: P. commune and P. uliginosum.