The North American species of Psathyrella.

1972]

PSATHYRELLA

111

apical pore present, shape in face view oblong to elliptic, in profile oblong to
subelliptic or obscurely inequilateral, color in KOH dark rusty brown slowly
becoming dark chocolate-color or fuscous-violaceous, in Melzer's reddish tawny,
wall about 0.5 A thick.
Basidia 4-spored, 18-23 x 7-9 t, hyaline in KOH, projecting about one third
to one half their length when sporulating. Brachybasidioles globose to nearly
so, 8-10 / wide. Pleurocystidia 38-47(-52) x 10-17 t, utriform or subutriform,
ventricose-subcapitate or fusoid-ventricose with obtuse apex, all hyaline, thinwalled, and smooth (as revived in KOH), content not distinctive (in KOH or
Melzer's). Cheilocystidia vesiculose to saccate and with yellowish walls for
the most part as revived in KOH, 10-16 ft wide, present as scattered cells near
the edge at times. Caulocystidia present as clavate to vesiculose cells much like
the cheilocystidia.
Pileus cuticle a layer about 2 cells deep of smooth, hyaline, thin-walled
vesiculose cells lacking distinctive content in KOH or in Melzer's. Hyphae of
the trama next to the cuticle smooth, weakly cinnamon, fading to pale dingy
ochraceous and lacking distinctive content. Clamps present.
Type locality. Upper Priest River, Bonner County, Idaho.
Habit and habitat. Gregarious under cottonwood trees on debris, October.
Distribution. Idaho.
Observations. The distinguishing features of this species are the presence of
brachybasidioles in the hymenium, the variable pleurocystidia, vesiculose to
clavate yellow cheilocystidia as revived in KOH, the almost oblong spores in face
view, and the delicate nature of the fresh basidiocarps. The species is placed here
on the assumption that the veil was appendiculate on the margin at first.
Material examined. Idaho: Smith 73946, 76781 (Type).
70. Psathyrella semivestita (Berkeley & Broome) A. H. Smith, Contr. Univ. Herb.
5:57. 1941.
Agaricus semivestitus Berkeley & Broome, Ann. Mag. Nat. Hist. III 7:376. 1861.
Drosophila gossypina var. semivestita (Berk. & Br.) Quelet, Flor. Mycol. 62. 1888.
Illust. Berkeley & Broome, op. cit., pl. 14. Text Figs. 181-183.
Pileus 10-30 mm broad, ovoid to obtusely conic when young, becoming
campanulate to convex, at times remaining unexpanded but with a flaring margin,
surface more or less glabrous around the disc, with white fascicles of fibrils near
the appendiculate or fringed margin, not scaly, soon glabrescent, striatulate when
moist, color variable, "Mars brown," "cinnamon-brown" or "Prout's brown"
when fresh and moist, (dark rusty brown to yellowish brown), hygrophanous
and fading to near "wood brown" or a sordid tan, usually fading along the
margin first. Context very thin, moderately fragile, cinnamon-brown when moist,
sordid tan when faded, odor and taste mild.
Lamellae ascending but bluntly adnate and soon seceding, close, 3 tiers of
lamellulae, moderately broad (23 mm), pallid at first, soon becoming "wood
brown," edges even.
Stipe 4-12 cm long, 1.5-3 mm thick, equal, strict, tubular, fragile, delicately
appressed fibrillose from scant veil remnants, apex pruinose, base faintly mycelioid, more or less glabrescent in age, white, becoming pale dingy honey-color on
lower portion.
Spores 10-12 (-14) x 5.5-6.5 I, smooth, apical pore distinct and apex truncate,
shape in face view elliptic to narrowly ovate, in profile subelliptic to very ob