The North American species of Psathyrella.

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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

[VOL. 24

Key to the Series of Subsection Limicolae
1. Habitat various as follows: On burned areas, under sagebrush, on Sphagnum,
and in alpine habitats including volcanic ash. series Boreales.
1. Habitat on wood or soil, muck, humus, etc. series Limicolae.
Series Boreales A. H. Smith, ser. nov.
Habitationis specialis. Typus. Psathyrella borealis.
Key to the Species of Series Boreales
1. On burned areas; spores 8-10 X 5-6. 372. P. ambusta.
1. Not as above. 2
2. Growing under or near sagebrush. 3
2. Not as above. 4
3. Stipe shining white; spores 8-10X4.5-5 u. 403. P. grasmerensis.
3. Stipe soon brownish below; spores 7-9 X 5-6(-6.5) j. 373. P. deserticola.
4. Habitat on Sphagnum. 5
4. Not on Sphagnum. 6
5. Spores 8-10 X 4-5 A; veil rudimentary. 374. P. borealis.
5. Spores 6.5-8 X 4-4.5 u; veil fibrils usually present on pilear margin. 375. P. paludosa.
6. Hyphae of cortex of stipe with content in part of particles of highly refractive
amorphous debris; growing on volcanic ash. 376. P. katmaiensis.
6. Not as above. 7
7. On barren sandy soil. see 389. P. seymourensis and 407. P. parva.
7. Not as above. 8
8. Pleurocystidia subeylindric to narrowly subfusoid; on exposed soil above
timberline. 377. P. mazamensis.
8. Pleurocystidia typically fusoid-ventricose. 9
9. Walls of cells comprising the pileus cuticle rusty to pale cinnamon in KOH;
basidiocarp with aspect of a Deconica. 378. P. psilocyboides.
9. Cuticular cells with ochraceous to hyaline walls in KOH. 379. P. boulderensis.
372. Psathyrella ambusta A. H. Smith, sp. nov.
Pileus 1-3 cm latus, demum plano-umbonatus, sordide fulvus, glaber; contextu
pallide fulvus; lamellae confertae latae brunneolae demum fusco-brunneae; stipes
3-4 cm longus, 2.5-4 mm crassus, pallidus, dissiliens, sparse fibrillosus; sporae
8-10x 5-6 /; pleurocystidia 40-58 (-62) x 10-14 tt, fusoide ventricosa, obtusa vel
acuta, interdum bifurcata; fibulae adsunt. Typus. Smith 34408 (MICH); legit
prope French Creek, Medicine Bow Mountains, Wyoming.
Illust. Text Figs. 751-753.
Pileus 1-3 cm broad, obtuse with a straight margin, expanding to plane with
a slight umbo, surface moist and hygrophanous, dull tawny to near cinnamonbrown except for pallid margin, fading to cinnamon-buff and in age the cuticle
checking into flat scales; veil very thin and showing only a fringe of fibrils along
the margin when it breaks. Context thin, concolorous with surface, odor and taste
none.
Lamellae close, broad, adnate-seceding, pallid brownish becoming dull
chocolate-brown to near drab.
Stipe 3-4 cm long, 2.5-4 mm thick, equal or narrowed downward and sunken
in the soil, moderately cartilaginous, whitish, hollow, splitting, surface fibrillose
from the thin veil, fibrillose-striate.
Spores 8-10 x 5-6 ~/, smooth, apical pore distinct and apex somewhat truncate,
shape in face view ovate to elliptic, in profile somewhat inequilateral to obscurely
ovate, in Melzer's tawny to reddish tawny, wall about 0.3 u thick.