Arctoa (2019) 28: 105–117
The genus Haplohymenium in Russia is represented by four species, including H. sieboldii, reported for the first time for the country, in southern regions of Primorsky Territory and Transbaikalia. This species is very closely related to H. triste and their distinction is discussed in detail. Haplohymenium longinerve is usually described as an easlily recognizable species due to unipapillose laminal cells, whereas in all other species the cells are multipapillose. However the variation in papillosity is drastic in this species. Different expressions of pseudounipapillose pattern of Haplohymenium longinerve are illustrated with different microscopy techniques, revealing a quite delicate structure of large conic papillae, making this character applicable with caution.