Diagnostic characters, ecology, and distribution of Ephemerum serratum (Hedw.) Hampe and Ephemerum stoloniferum (Hedw.) L.T.Ellis & M.J.Price in Austria

The taxonomy of Ephemerum serratum and Ephemerum stoloniferum has been debated for over a century, primarily due to early misinterpretations of key diagnostic characters. Consequently, these two species were often not distinguished in taxonomic identifications, leading to a significant lack of reliable data on their distribution and ecology. To address these gaps, I analyzed 98 herbarium specimens, focusing on morphological and ecological parameters. Spore size and ornamentation emerged as the most definitive differentiating characters. The average spore size of E. serratum was 54 ± 6 µm, whereas E. stoloniferum had a mean spore size of 72 ± 7 µm, with minimal overlap. Additionally, E. serratum spores exhibit a finely papillose or smooth surface, while those of E. stoloniferum are coarsely warty. The frequently cited hyaline veil proved to be an unreliable diagnostic feature, as it could be present in both species. The ecological analysis revealed significant differences in precipitation levels between the species (p < 0.05), with E. stoloniferum occurring at lower elevations with reduced precipitation, although the altitude difference was not statistically significant. No habitat differences were observed between the analyzed samples. Regarding geographic distribution, E. serratum was found in all Austrian provinces, whereas E. stoloniferum was restricted to Burgenland, Lower Austria, Salzburg, Styria, and Vienna. These findings provide a clearer taxonomic and ecological framework for distinguishing these species and contribute to a better understanding of their distribution patterns.