During a foray in Pasvik, Finnmark in north Norway, August 2011, a Mycena species unknown to me was collected by two of the participants. It pretty much looked like Mycena cinerella; it even possessed a farinaceous smell, but a microscopic investigation showed completely different characters. The material remained unidentified and was put away for future examinations.
One year later, the same taxon was collected in an alpine area in south Norway. Once again it was misidentified as M. cinerella in the field, but again showing the characteristic microscopic features as in the taxon from Finnmark. This observation gave birth to the idea that this was a taxon typical of arctic and alpine areas. I therefore examined all the alpine collections of M. cinerella in the herbarium of Oslo and found one more collection of the new taxon, collected in 2005 at Finse in south Norway.  The two next years the taxon was found in two new localities. It is also present among Gro Gulden´s collections from Finse 1980, identified as M. cinerella. The new species, named Mycena pasvikensis (Aronsen 2016), has now been collected in six different counties in Norway. All records have been done in alpine localities at an altitude of 900 – 1200 m, except for the two collections from Finnmark and Aust-Agder.

Etymology – from Pasvik, the first locality where it was noticed.

Pileus 7-13 mm across, conical to convex, translucent-striate, shallowly sulcate, hygrophanous, glabrous, dark brown to greyish brown, mostly with a paler margin.  Lamellae 15-19 reaching the stipe, arcuate, broadly adnate, decurrent with a tooth, grey to pale greyish brown, edge concolorous or paler. Stipe 15-55 x 0.5-1.5 mm, hollow, equal, straight to somewhat flexuous, terete, glabrous, but pruinose at the apex, somewhat lubricous when moist, somewhat firm, whitish grey at the apex, grey to grey-brown farther down, becoming more brownish with age, the base densely covered with long, flexuous, white, fibrils. Odour strongly farinaceous but rather fugacious, and then experienced as indistinct. Taste noticed as farinaceous (Corriol & Jargeat 2023).

Basidia 23-31 x 6.5-10 µm, clavate, 4-spored, with sterigmata up to 7 µm long. Spores 7.8-10(-11) x 4-5.4 µm, pip-shaped to somewhat cylindrical, Q 1.6-2.2, Qav ≈ 1.8, smooth, amyloid. Cheilocystidia (without excrescences) 13-25 x 5-20 µm, occurring mixed with basidia but sometimes partly forming a sterile band, scarce to numerous, not embedded in gelatinous matter, clavate, rarely ovoid, subcylindrical or pyriform, covered apically with one to few, straight to flexuous, simple to somewhat branched, cylindrical projections 1.5-45 x 1-4 µm, of which one usually is much longer than the others, rarely smooth or covered with only a few very short excrescences. Pleurocystidia not observed. Lamellar trama dextrinoid. Hyphae of the pileipellis 1-5 µm wide, covered with simple to branched, cylindrical excrescences 1-5(-20) x 0.2-2.5 µm, which may form dense masses and tend to become somewhat gelatinized. Hyphae of the cortical layer of the stipe 1-3(-5) µm wide, smooth to covered with cylindrical excrescences 1-4.5 x 0.5-1 µm, embedded in gelatinous matter, terminal cells 3-4 µm wide, narrowly clavate, diverticulate. Clamp connections present at all tissues.

Gregarious among litter or in moss in alpine Salix shrubs. One collection from lowland, on moss covered grassland. Autumn.

Microphotos of cheilocystidia -1

Microphotos of cheilocystidia -2

Microphotos of cheilocystidia -3

Microphotos of the hyphae of the pileipellis

Microphotos of the hyphae of the cortical layer of the stipe

As mentioned above, Mycena pasvikensis can be confused with M. cinerella in the field. M. pasvikensis seems to be almost exclusively alpine-arctic but occasionally M. cinerella too can occur in the same habitats. Both species have a farinaceous smell and decurrent lammellae. However, M. pasvikensis usually has a more brownish pileus. Microscopically the two species are very different, particularly in the shape of the cheilocystidia. Besides, in M. cinerella the lamellar edge is homogenous sterile, while in M. pasvikensis the cheilocystidia are occuring among basidia (lamellar edge heterogenous).

There are not yet many records of M. pasvikensis from Norway but the distribution indicates that it probably is not very rare. More likely, it has been misidentified as M. cinerella and overlooked.
Recently it was also recorded in Gremany (Dr. L. Kriegelsteiner pers. comm.). Pilzkunde.de

Corriol & Jargeat (2023) reported on a collection from the French alps (Savoie) at a altitude of 2400 meters. They did not observe the typical shape of the cheilocystidia seen in all Norwegian collections, but found cheilocystidia more similar to those in M. cinerella, although mixed with basidia and rendering the lamella heterogenous. They measured somewhat smaller spores than in Norwegian collections. The identity was confirmed by ITS sequencing.

Examined material:

NORWAY: FINNMARK, Sør-Varanger, Øvre Pasvik Nasjonalpark, UTM 35W NS 8099 5855, 18 Aug. 2011, in Sphagnum or Polytrichum,  leg. Inger Kristoffersen & Eddi Johannesen (holotype). HORDALAND, Ulvik, Finse, Fetene  UTM(WGS84): MN 193-195 177-183, 10.09.1980, 1205 m.o.h., Rumiceto-Salicetum lapponae, leg. Gro Gulden 615/80 – O-302546, Gro Gulden 612/80 – O-302543, Gro Gulden  614/80 – O-30254, and Gro Gulden  616/80 – O-302547;  Ulvik, Finse, Fetene 26.10.2005, in moss under Salix sp., 1200 m.o.h., leg. A. Aronsen A 25/05 – O-286602. SOGN OG FJORDANE, Lærdal, Hemsedalsfjellet 30.09.2012, alpine Salix shrubs, 1100 m.o.h., leg. I. Kristoffersen & A. Aronsen; 21.09.2013, in moss among Salix shrubs, leg. A. Aronsen. BUSKERUD, Hemsedal, Hemsedalsfjellet ved Slettevatnet UTM 32V MN 54678 59574, 21.09.2013, in alpine Salix shrubs, 1130 m.o.h., leg. A. Aronsen A45/13; Hemsedal, Hemsedalsfjellet ved Heimretjernet, UTM 32V MN 55061 57456, 22.09.2013, in alpine Salix shrubs, 1100 m.o.h., leg. A. Aronsen. TELEMARK, Tinn, ved Møsvann, UTM 32V MM 60605 30873, 14.09.2014, in alpine Salix shrubs, 930 m.o.h, leg. A. Aronsen. AUST-AGDER, Froland, Hynnekleiv stasjon, 32vmk66089569 (±10m) UTM(WGS 84), 25.09.2016, Mosedekket gammel plen med lågurtpreg på gammelt jenbanestasjonsområde, leg. Inger-Lise Fonneland, Dag Pettersen, Jytte Birk Kaas, Asbjørn Lie, Roar Linjord (Artsobservasjoner).