This species has become confused in the literature, although it seems to have been picked up by field guides as a generic name for small brown thin mushrooms on moss covered logs.
The problem seems to come from the idea of “calyptrate” spores, which Smith and Singer site as a taxonomically character. This is where the outer covering of the spore pulls away from the plage area to display “flaps” at the edges of the spore. Smith and Singer, in 1964, from the study of North American samples, decided that the 1935 species published by Kuhner from Europe, was not calyptrate, and spores were roughened. Also they went on to display drawings of the cystidia which has acute apecies.
In all recent studies of Galerina from Europe (Watling and Gregory 1993, Haan and Walleyn 2002, Gulden 2006), people have taken a different tack, and stated that the 1935 species is calyptrate, and only slightly roughened to not roughened. Also that the cheilocystidia are blunt and thick.
There now seems to be two descriptions of this species, one from Europe that most are assuming is the true G. hypnorum, and a G. hypnorum sensu Smith and Singer.
There are other very similar species of Galerina, such as G. sahleri, with calyptrate spores, that are not roughened. Haan and Walleyn suggest that G. sahleri is equivilent to a species published by Kuhner – G. hypnorum f. calyptrospora. Perhaps more forms of G. hypnorum need to be defined to sort this out.
Funga Nordica (2008) may offer some clarification to the identity to G. hypnorum.
The species G. calyprospora Kuhner is indicated as the same species as G. sahleri (Quel.) Kuhner s. Favre (G. sahleri of Smith and Singer). The spore size of this species is given as 10.5-13 × 5.5 × 7 microns. The spore size of G. hypnorum (Schrank:Fr.) Kuhner s. Horak and de Haan & Walleyn is given as (7.5-)8-10(-10.5) x (4.5-)5-5.5(-6).
Note: Gro Gulden is the author of the section on Galerina in Funga Nordica.