Gregarious among mosses and fallen needles of Picea. Also found among Quercus leaves. Rare. Recorded in Austria, Finland, Germany, Italy, Norway and Switzerland.

Pileus 3-18(-20) mm across, conical, spreading with the margin becoming more or less upturned, without or with a small umbo, often somewhat sulcate, translucent-striate, hygrophanous, sepia brown or fairly dark grey-brown to dingy pale brownish at the centre, paler toward the margin, e.g. brownish cream to brownish white, pallescent on drying out. Flesh thin, concolorous with the surface of the pileus. Lamellae 16-24 reaching the stipe, ascending, c. 1.5 mm broad, somewhat ventricose, fairly narrowly adnate, at times dorsally intervenose, cream with some sepia shade, pale greyish brown to whitish, edge concolorous or paler. Stipe 30-60 x 0.5-1,5 mm wide, hollow, firm, somewhat flexuous, equal, smooth, glabrous, brownish whitish to pale brownish above, grey-brown to sepia brown below, base covered with coarse, long, flexuous, whitish fibrils. Odour and taste raphanoid, sometimes very pronounced, sometimes weak.

Basidia 26-35 x 6.5-10 µm, (narrowly) clavate, 4-spored. Spores 7-10.5 x 4.5-5.5(-6.5) µm, pip-shaped, smooth, strongly amyloid. Cheilocystidia 30-70(-80) x 12-30 µm, forming a sterile band, clavate, mostly long-stalked, above densely covered with evenly spaced, short, cylindrical excrescences. Pleurocystidia similar, not numerous. Lamellar trama dextrinoid, staining yellowish red-brown in Melzer's reagent. Hyphae of the pileipellis 2-17(-20) µm wide, covered with short, narrow, straight to curved, cylndrical excescences 0.5-2 x 0.5 µm. Hyphae of the stipitipellis 2-8 µm wide, densely covered with cylindrical excrescences 1-5 x 0.5-1 µm, terminal cells narrowly clavate, diverticulate. Clamps absent or very rare.

I have seen this species only once, and the description above has partly been taken from Maas Geesteranus (1984), which was based on Favre's notes. Maas Geesteranus never examined the type which "is not allowed to leave the herbarium" The information about the absence of clamps in the type was provided by Dr. O. Monhoux (G).

My experience with this rare species is based on one Finnish and one Nowegian collection that matched Favre's description perfectly except for smaller fruitbodies.

Mycena rapiolens is obviously allied to M. filopes and M. metata, but differs by the lack of the iodoform odour and the much wider hyphae of the pileipellis. Robich (2003), who reported M. rapiolens from Italy, claimed to have observed scattered clamps. He also reported larger spores (10-12 x 4.5-5.5 µm) and wider hyphae of the pileipellis (5-16[-23]). According to Robich the hyphae of the stipitipellis are 3-11 µm wide, densely covered with short, cylindrical excrescences. He did not observe any caulocystidia.

Vizzini (2005), however, who reported on another Italian collection and provided a very thorough discussion and comparison to related species, expressed some doubt about Robich's determination. As he wrote, Robich's collection possessed clamps, the spores were almost cylindrical and larger than Favre had reported for M. rapiolens, and he had not noticed any smell. The radish-like (raphanoid) smell was noticed by Miersch (1985) who reported on a German collection. This collection was found among fallen leaves of Qurecus.

Vizzini (2005) also pointed at the relationship to Mycena flavescens, a species with just as wide hyphae of the pileipellis. Besides, it has a disagreeable odour, often experienced as of raw potato but also as raphanoid. M. flavescens differs from M. rapiolens in having a yellow tinge at the pileus and the lamellae and a violaceous hue at the apex of the stipe. It is, however, a very variable species, and these colours can be completely absent in some collections. Microscopally M. flavescens differs in possessing clamps and having somewhat narrower hyphae of the stipitipellis. The differences between the two taxa will hopefully be better understood by more collections of M. rapiolens and perhaps by molecular studies.

Monthoux (1987) has also given a well annotated description of M. rapioles accompanied by a water colour made by Jeanne Favre.

M. rapiolens is characterized by:

A Finnish collection kindly put to my disposal by Mr. Jukka Vauras fits well with M. rapiolens:

Pileus 3-5 mm, conical to parabolical, translucent-striate, fairly dark, blackish brown or dark sepia brown with the margin much paler, brownish cream (see photo above). Odour and taste not recorded. Lamellae 16-17 reaching the stipe, ascending, narrowy adnate, dark grey, the edge paler. Stipe 35-60 x 0.5 mm, hollow, firm, straight to somewhat flexuous, equal, grey-brown, at the base covered with white fibrils.

Basidia 26-35 x 7.5-10 µm, clavate, 4-spored, with sterigmata up to 5 µm long. Spores 7-10 x 4.5-6 (-6.5) µm, pip-shaped, smooth, strongly amyloid. Cheilocystidia 30-59 x 12-22 µm, forming a sterile band, clavate, mostly long-stalked, densely covered with evenly spaced, short, cylindrical excrescences. Pleurocystidia not numerous, similar. Lamellar trama weakly dextrinoid, yellowish brown in Melzer's reagent. Hyphae of the pileipellis 2-17 (-20) µm wide, diverticulate, densely covered with short, narrow, straight to curved, cylindrical excrescences up to 2 x 0.5 µm. Among the hyphae are present some druze-formed elements, about 8 µm wide. Hyphae of the cortical layer of the stipe 2-8 µm wide, densely covered with cylindrical excrescences up to 5 x1 µm, terminal cells narrowly clavate, diverticulate. Clamp connections absent, very rare or hard to detect (clamp seen at the base of one basidium).

FINLAND: Koillismaa, Kuusamo, Oulanka National Park, in herb-rich forest with Picea abies, Pinus sylvestris, Betula, Alnus incana, Populus tremula and Salix, 3 Sept. 2005, leg. J. Vauras 23396F.

The specimens in this collection are rather small, and much smaller than the type. The colours, however, fit well with the type description, as do the microscopic features. The cheilocystidia are somewhat smaller than reported by Favre, and unfortunately no smell was recorded, but there should be no doubt that it represents M. rapiolens.

From Switzerland M. rapiolens is known from alpine areas at altitudes between 400 and 1000 m. The Italian record, however, was done at an altitude of 239 m in Torino. Oulanka National Park is located in the north of Finland with boreal forests, indicating that it can be found in different habitats.