Ptychostomum touwii, a new bryophyte species distinguished from Ptychostomum rubens by iterative morpho-molecular analysis, and a note on Bryum microerythrocarpum

DNA barcoding of Dutch collections of Ptychostomum rubens (Mitt.) Holyoak & N. Pedersen as understood in modern Floras revealed two distinct taxa. A morphological study of these specimens recognized several characters which can be used for identification. Ptychostomum rubens as well as its synonym Bryum bomanssonii Lindb. are lectotypified here. These lectotypes, and hence these two taxa, belong to the same morpho-molecular species. The other species is described here as a new species: Ptychostomum touwii Bijlsma, Kruijer & M. Stech. A key to these two species and the closely related P. bornholmense (Wink. & R. Ruthe) Holyoak & N. Pedersen is given. Their distribution and ecology in the Netherlands are briefly discussed. Ptychostomum rubens is a widespread species in the Netherlands, occurring on disturbed, base-rich, often calcareous and nutrient-rich soils, whereas P. touwii is calcifuge and prefers disturbed, less nutrient-rich, sandy soils and loams. The distribution range of the latter species needs to be clarified yet. After studying material from the South American species Bryum subapiculatum Hampe, B. dentiferum Hampe, and B. rubrinerve Cardot & Broth., we propose to exclude these species from the species concept of B. microerythrocarpum Müll.Hal. & Kindb. awaiting further molecular research of this variable species complex. Since, based on previous molecular research, B. subapiculatum is recently classified in the genus Imbribryum N. Pedersen and B. subapiculatum and B. microerythrocarpum are closely related, we also make the new combination Imbribryum microerythrocarpum (Müll.Hal. & Kindb.) Bijlsma, Kruijer & M. Stech.