The North American species of Psathyrella.

1972]

PSATHYRELLA

133

88. Psathyrella albescens Hesler & A. H. Smith, sp. nov.
Pileus 5-7 cm latus, convexus demum planus subspadiceus demum pallidus,
ad marginem appendiculatus, saepe radiate rugulosus; lamellae latae adnatae
demum subdistantes pallide argillaceae demum fusco-brunneae; stipes 6-8 cm
longus 5-6 mm crassus palidus sursum furfuraceus; sporae 7-8.5x3.5-4.5 pu;
pleurocystidia (28-)35-56(-64) x14-17(-20) f; fibulae adsunt. Typus. Hesler
18895 (MICH); legit L. R. Hesler prope Farragut, Knox County, Tennessee.
Illust. P1. 45; P1. 79, fig. b; Text Figs. 218-221.
Pileus 5-7 cm broad, hemispheric, expanding to convex or nearly plane, moist
but not viscid, hygrophanous, dark yellowish brown ("Dresden brown") when
moist, fading to whitish or "pale vinaceous-buff," mature pilei mostly whitish
when dried, slightly atomate, appearing striatulate, in some radially rugulose, at
first margin appendiculate from remains of a thin white veil. Context thin, pallid,
odor and taste mild.
Lamellae adnate to slightly decurrent, whitish to pale pinkish buff at first,
"snuff brown" at maturity but more purplish in age from spores, in dried basidiocarps having a cocoa-colored tinge, rather broad, narrowed somewhat in front,
close, edge fimbriate.
Stipe 6-8 cm long, 5-6 mm thick, strict, hollow, whitish, a few dark fibrils
present, apex white-mealy to squamulose, base curved.
Spores "blackish brown (1)" in deposit, 7-8.5 x 3.5-4.5,, smooth, apical pore
distinct, shape in face view oblong to elliptic, in profile slightly bean-shaped to
obscurely inequilateral, when revived in KOH dark cocoa-color slowly changing
to dark chocolate-color, in Melzer's reddish tawny, wall about 0.3 / thick.
Basidia 4-spored, 18-24x6-7 /A, narrowly clavate, hyaline in KOH. Pleurocystidia abundant (28-)35-56(-64) x14-17(-20) A, variable in shape from
subglobose-pedicellate to ellipsoid-pedicellate but mostly ventricose with obtuse
to rounded or subcapitate apex, thin-walled, smooth, hyaline in KOH, content not
distinctive in KOH or Melzer's. Cheilocystidia mostly subglobose to clavate,
18-28 x 10-17 A, in old basidiocarps some having highly refractive localized
deposits of material on the interior face of the wall (these may appear as highly
refractive wall thickenings). Caulocystidia variable in size and shape.
Gill trama regular, the cells becoming greatly enlarged in age, dull brownish
in KOH but fading. Pileus with a cuticle in the form of a layer of inflated cells
two or three deep but with many clavate-pedicellate cells intermixed and over the
disc more or less forming a palisade, in old basidiocarps many of the cells with
the highly refractive deposit noted for the cheilocystidia. Hyphae of the trama
when first revived in KOH cocoa-color but fading to sordid brownish or hyaline.
Clamp connections present. No distinctive reaction on any tissue when mounted
in Melzer's.
Type locality. Farragut, Knox County, Tennessee.
Habit and habitat. Scattered on piles of chips.
Distribution. Colorado, Idaho, Massachusetts, Michigan, Tennessee.
Observations. Romagnesi (in Kiihner and Romagnesi, 1953) described Drosophila exalbicans which appears to be somewhat similar to P. albescens but has
spores often elongate-subtriangular, and a very slight veil. He also describes
D. exalbicans as having pale to medium pale spores. Because of these differences
I do not consider his species the same as P. albescens.
Material examined. Colorado: Smith 51822. Idaho: Smith 44653. Massa