The North American species of Psathyrella.

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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

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Illust. Text Figs. 415-417.
Pileus 8-15 mm broad, obtuse with an appressed margin when young, expanding to broadly convex or retaining a slight umbo, surface at first covered by the
white fibrillose remains of the outer veil, soon fibrillose-scaly and finally glabrous,
the margin at first appendiculate with fragments of the veil or merely fringed,
evenly dull reddish brown, hygrophanous, more or less avellaneous when faded.
Context very thin and fragile, odor and taste not recorded.
Lamellae broad, subdistant, 1-2 tiers of lamellulae, bluntly adnate, dark
reddish brown ("carob brown") at maturity, edges slightly fimbriate.
Stipe 1.5-2.5 cm long, up to 1.5 mm thick, equal, fragile, white, densely
fibrillose over lower portion, pruinose above.
Spores 6-7.5 (-8) x 3-3.5 I, smooth, apical pore present but apex not truncate,
shape in face view narrowly elliptic to oblong, in profile obscurely inequilateral
to obscurely bean-shaped, color in KOH chocolate color and slowly becoming
slightly darker, in Melzer's reddish tawny, wall about 0.2 / thick.
Basidia 4-spored, 18-22x5-7 I, clavate, hyaline in KOH. Pleurocystidia
scattered to abundant, 36-48x 7-13 pu, narrowly fusoid-ventricose with subacute
apex, or shorter (about 32 x 14 p) and with a more rounded apex, the latter type
not abundant, wall thin, smooth and hyaline, cell content not distinctive in KOH
or Melzer's. Cheilocystidia similar to pleurocystidia or clavate to globose and
12-18x8-13,u, hyaline in KOH. Caulocystidia similar to the cheilocystidia.
Gill trama regular, pale to moderately dark cocoa-color in KOH (nearly
hyaline in thin sections). Pileus trama cocoa-color in KOH, hyphal walls smooth
or practically so. Cuticle of pileus formed by a layer of inflated hyaline cells
several deep, the walls hyaline to weakly cinnamon in KOH, cell content not
distinctive. Clamp connections present. No distinctive reaction noted on any
tissue mounted in Melzer's.
Type locality. Near Stockbridge, Michigan.
Habit and habitat. Gregarious on debris under a brush pile (in hardwoods).
Distribution. Michigan.
Observations. This species might be sought for under section Appendiculatae
in this work as the margin in a few basidiocarps was truly appendiculate. The
small spores are distinctive in comparisons with the P. fibrillosa group.
Material examined. Michigan: Potter 6355, Smith 32-455 (Type), 36067.
Stirps Fibrillosa
Key to the Species of Stirps Fibrillosa
1. Many pleurocystidia having 1-3 finger-like projections at or near the apex.
184. P. cornifericystis.
1. Not as above-only rarely one finds a cystidium having projections. 2
2. Spores bright ochraceous-tawny when first mounted in KOH; basidiocarps
typically cespitose. 185. P. subcaespitosa.
2. Not as above (spores cocoa-color revived in KOH). 3
3. Stipe and pileus drying violaceous umber to violaceous-cinereous; spore apex
distinctly truncate; cuticle of pileus 2-3 cell deep. 186. P. umbrinescens.
3. Not as above. 4
4. Habitat on sphagnum. 187. P. laurentiana.
4. Not as above. 5
5. Spores 8-11 X 4-5 /u. 6
5. Spores 6-9 X 3-4.5 tz (rarely 5-6,u wide). 7
6. Stipe 3-5.5 cm long; pleurocystidia (at least some) having dingy vinaceousbrown tints in KOH. 193. P. harrisonii.