Basidiomata scattered on the ground under Juniperus communis. Autumn. Only the holotype is known from Norway. Robich
(2003: 238- 241) reported it from Italy. He also provided
a colour photo.
Pileus (dried) up
to 8 mm across, convex, without umbo, sulcate, pruinose,
grey-brown. Flesh thin. Odour
not recorded. Lamellae 16 reaching
the stipe, tender, ascending, c. 1 mm broad, somewhat ventricose,
adnate, decurrent with a short tooth, grey, the edge convex,
pallid. Stipe (dried) 35-45 x
1 mm, hollow, fragile, equal, terete, apically densely pruinose,
glabrous farther below, grey-brown, the base densely covered
with long, coarse, white fibrils.
x 7-9 µm, clavate, 4-spored, clamped, with sterigmata
5.5-6.5 µm long. Spores
7.6-8.2 x 4.9-5.5 µm,pip-shaped, smooth, amyloid.
27-50 x 9-19 x 0-4.5 µm, fusiform, sublageniform (a
few without neck and more ellipsoid), clamped, smooth. Pleurocystidia
not numerous, mostly without neck, ellipsoid. Lamellar
trama brownish vinescent in Melzer's reagent.
of the pileipellis 1.8-2.5
µm wide, clamped, covered with simple or furcate to
somewhat branched, cylindrical excrescences 1.8-15 x 1.5-2
of the cortical layer of the stipe 1.8-2.5
µm wide, clamped, sparsely covered with simple to
furcate, curved to more or less coiled excrescences 2-9
x 1-2 µm, the
terminal cells 4.5-8 µm broad, variously
shaped and generally coarsely diverticulate.
The description has been taken entirely from Maas
Geesteranus (1993: 337-338).
Mycena aronsenii belongs to sect.
Fragilipedes where it comes close to M. leptocephala. The latter differs in having smooth
hyphae of the cortical layer of the stipe, generally with
much inflated caulocystidia, larger spores, and the hyphae
of the pileipellis tending to become somewhat gelatinized.
Following the key in Maas Geesteranus (1992) M. aronsenii comes close to
M. abramsii (Murill) Murill and M.
aetites (Fr.) Quél. The first species has, among other things,
more lamellae reaching the stipe (19-27), larger spores,
and differently shaped excrescences of the hyphae of the
stipe. The latter has, among several differences, differently
shaped cheilocystidia, larger spores, and different shape
of the excrescences of the hyphae of the stipe.
M. aronsenii belongs to a very difficult complex within sect. Fragilipedes, and the type was poorly annotated macroscopally. A recent attempt (2022) to obtain an ITS sequence from the holotype unfortunately was unsuccessfull. For the time being I reluctantly accept it as a separate species.
VESTFOLD, TJØME, Hvasser,
Sønstegård, gregarious under Juniperus,
4 Nov. 1989, A. Aronsen A 67/89 (No. 989.027-053; L).