The North American species of Psathyrella.

1972]

PSATHYRELLA

371

on them, no distinctive reaction on any tissue in mounts made in Melzer's. Clamps
present.
Type locality. Tahquamenon Falls State Park, Luce County, Michigan.
Habit and habitat. Gregarious on a very decayed log of a hardwood tree.
Distribution. Maine, Michigan, New York.
Observations. The distinctive features of P. parvifibrillosa are the thin
fibrillose outer veil, cinnamon to tawny colors, the stipe darkening appreciably
at the base, the variable spore size and shape, and the lignicolous habitat. It
may be characterized as a very commonplace Psathyrella.
Material examined. Maine: Bigelow 3738, 3742, 3743, 3745, 3906. Michigan:
Smith 36516, 39069 (Type). New York: Shaffer 448.
Section Obtusatae (Fr.) Singer,
Agar. Modern Taxon. 509. 1962 (excluding synonymy)
Veil remnants on pileus greatly reduced to absent, often present as a thin
coating of fibrils along the margin; spores up to 10(-11) u long; pleurocystidia
acute to obtuse (rarely broadly rounded and if so then these mixed with others
merely obtuse at apex).
Type. Psathyrella obtusata.
Key to the Subsections of Section Obtusatae
1. Densely cespitose on wood or humus. subsect. Caespitosae.
1. Solitary to gregarious or in small clusters. 2
2. On wood (or often very rotten remains of logs etc. or on chip dirt).
subsect. Obtusatae.
2. Truly terrestrial (but stipe may be attached to small sticks), or on Sphagnum,
lichens, or on compost. subsect. Limicolae.
Subsection Caespitosae A. H. Smith, subsect. nov.
Caespitosae. Typus. Psathyrella multipedata
Key to the Species of Subsection Caespitosae
1. Veil remnants forming a fibrillose volva near base of stipe. 345. P. columbiana.
1. Not as above. 2
2. Spores 5-6 X 2-3.5 A (see 78. P. confertissima also). 346. P. fragrans.
2. Spores larger. 3
3. Veil buff colored. 347. P. mucrocystis.
3. Veil, if present, white. 4
4. Cluster of basidiocarps arising from a well-developed pseudorhiza.
348. P. multipedata.
4. Not as above. 5
5. Spores 8-10(-11) X 4.5-6 /i. 6
5. Spores smaller (see 211. P. polycephala and related species also). 8
6. Pleurocystidia 48-64 L long. 7
6. Pleurocystidia 26-38(-45) X 8-12 u; stipe 6-12 cm long. 349. P. longistipes.
7. Spores dark coffee brown in KOH, slowly becoming chocolate-color; stipe white
over all. 350. P. rugoradiata.
7. Spores cocoa-brown at first in KOH; stipe brownish in age. 351. P. baragensis.
8. Pleurocystidia very variable in shape. 352. P. heterocystis.
8. Not as above. 9
9. Spores 6.2-7.5 X 3.5-4 IL. 353. P. acuticystis.
9. Spores 7-9 AI long. 10
10. Spores truncate. 354. P. ophirensis.
10. Spores not truncate. 355. P. microsperma.