A comparative study of the mosses Ptychostomum pseudotriquetrum and P. bimum : Investigating morphological characters, habitat, and distribution across northern Sweden

Abstract: The mosses Ptychostomum pseudotriquetrum and P. bimum (syn: Bryum, Bryophyta) are difficult to distinguish from each other, as they appear morphologically identical besides their difference in sexual condition. Because of their similarities, some researchers treat both as P. pseudotriquetrum, while others treat them as two distinct species. Previous studies have described differences in characters besides sexual condition. However, there are few such studies, and none has been conducted in northern Sweden. The purpose of this study was to investigate if P. pseudotriquetrum and P. bimum could be distinguished by characters other than the sexual condition and study the environmental preferences and distributions of the species in northern Sweden. Thirty-three specimens were used in the study. Ten different characters were examined, and morphological data were collected and analyzed for differences. Information regarding habitat and distribution were gathered and analyzed. The statistical analyses showed a significant difference in the leaf decurrency between the species, and an almost significant difference regarding stem length and shape of median leaf lamina cells. No other differences were found. The results correspond with previous research claiming P. pseudotriquetrum and P. bimum should be considered two distinct taxa. The difference in leaf decurrency suggests that this character might be useful in future research to distinguish the two species, especially when the study samples are sterile, or when there is a lack of molecular data to confirm the species identification. At present the two species are best regarded as semi-cryptic, pending further detailed investigations of potentially distinguishing characters.