Gregarious under Alnus incana (and more rarely Picea abies). Not found in Norway.

Pileus up to 50 mm across, at first convex, remaining so or becoming irregularly plane with an undulating partly elevated margin, glabrous, hygrophanous, weakly translucent-striate when moist, sordid lilac when fresh, more brownish in age; surface dry, slightly rugose. Lamellae 28 to more than 30 reaching the stipe, ascending, adnate to broadly adnate or almost decurrent, becoming dorsally intervenose, sordid lilac, densely punctate by minute, dark purplish brown dots (pleurocystidia), and with entirely dark violet edge. Stipe up to 70 x 10 mm, widened downwards but basally narrower, hollow, straight, curved below, terete, covered with conspicuous, very small dark granules at the apex, dry, pale sordid lilac, yellowish at the base. Odour distinctly of radish. Taste mild, of radish. All parts of the basidiocarp often blackening when drying.

Basidia 27-30 x 6.5-8 µm, slender-clavate, 4-spored, clamped. Spores (6.0-)7.5-9.0 x (3.5-)4.0-5.0 µm, pip-shaped or somewhat elongated pip-shaped, smooth, weakly amyloid. Cheilocystidia 43-70 x 7-12 µm, occuring mixed with the basidia, strongly protruding, fusiform, with long, narrow necks, clamped, with purplish brown contents. Pleurocystidia numerous, similar, but often shorter, with purplish brown contents. Hyphae of the pileipellis up to 3.5 µm wide, smooth. Hyphae of the cortical layer of the stipe up to 2.5 µm wide, smooth, the terminal cells cylindrical, curved outwards.

The macroscopic description has been taken from Harmaja's and Maas Geesteranus' descriptions complemented by my own observations on the dried material. The microscopic details are based on examination of four Finnish collections.

Harmaja (1985: 44) described the until then unknown species M. lammiensis as growing in Finland under Alnus incana (and more rarely Picea abies). It shares many features with M. pelianthina, like the violaceous tints, the raphanoid smell, and the dark violet lamellar edge. Microscopically the two species are quite similar too, the only distinct difference being the spore size. In M. pelianthina the spores rarely are more than 4 µm broad, while in M. lammiensis they are almost always broader than 4 µm. (According to my measurements (6.0-)7.5-9.0 x (3.5-)4.0-5.0 µm). The shape of the spores may be somewhat different too. In M. pelianthina the spores are somewhat narrowly pip-shaped, while in M. lammiensis they are pip-shaped to somewhat cylindrical. This is, however, hardly a distinct specific character. Harmaja claimed that the cystidia of M. lammiensis were narrower than the counterparts in M. pelianthina, and that they had longer and narrower necks. Although the outer measurements do not differ much, my impression is that Harmaja is right on this point. The cheilocystidia generally seem to be narrower and with narrower and longer necks in M. lammiensis. Another difference is that the cheilocystidia are much more protruding in M. lammiensis than the counterparts in M. pelianthina.

It is not clear to me whether the colour of the pileus is different between the two species. In Mycena pelianthina the colour is date brown to pale brown with purplish to violaceous tinges, drying to pale ochraceous or beige, with or without a pinkish shade. The descriptions of M. lammiensis suggest a more dingy lilac colour, which is turning more brownish with age. The blackening process when drying seems to be similar in both species.

Harmaja (1985) and Maas Geesteranus (1992: 405) discussed the very slight differences between M. lammiensis and the American species M. rutilantiformis, and concluded somewhat hesitantly that M. lammiensis is a species in its own right. I am not all that convinced by the arguments.

To my knowledge M. lammiensis has been reported from four localities in Finland. Two localities were close to each other in Lammi, South Finland, the third was near Vehmersalmi in East Finland (two different collections), and the fourth were from Kalajoki in West Finland. Mycena pelianthina has been collected in Finland in Uusimaa, Helsinki and Parainen, Åntala.

An interesting question is if the Norwegian collections of M. pelianthina, collected under Alnus, from central and Northern parts of the country actually would prove to represent M. lammiensis. Examination of three collections from the herbarium in Oslo, and five collections from Tromsø, however, showed without doubt that they are M. pelianthina. M.lammiensis has still not been recorded in Norway.

I will express my thanks to the authorities of the herbarium in Helsinki for the loan of the holotype of M. lammiensis and an additional collection from Turku (Leg. S. Huhtinen, 30 Aug. 1985).

Mycena lammiensis belongs to the section Calodontes (Fr. ex Berk.) Quél. on account of the large size, the purplish or violaceous tints, and the raphanoid odour. Within this section it is placed in subsection Marginatae J. E. Lange together with M. Pelianthina (Fr.) Quél. and M. rutilantiformis (Murrill) Murrill because of the intensely coloured lamellar edge. The latter has only been recorded from the United States. Harmaja (2002) transferred Mycena lammiensis to the genus Prunulus, a point of view that has not been followed at this web site.

Collections examined:

FINLAND:
Etelä-Häme: Lammi, Hauhiala, S shore of Lamminjärvi 5 Sept. 1978, Anne Sairanen (Holotype, H)
Sb, Vehmersalmi, Puutosmäki, Pitkälahti, grid 6956:541, by the old limestone quarries, thicket of Alnus, with Daphne, Populus tremula 30 Aug. 1985, S. Huhtinen 85/85 (TUR)
PS. Vehmersalmi, (Soisalo), Puutosmäki, grid 27° E: 69568:5413, 12 Aug. 1992, Pekka Heinonen 60-92 (TUR).
Keski-Pohjanmaa, Kalajoki commune, Rahja-Roukala, grid 27° E: 7125:341, damp, herb-rich forest with mainly Alnus incana and scattered Prunus padus, Picea abies, and Betula, on litter 11. Sept. 2004, Katri Kokkonen 271/04 (TUR).