The North American species of Psathyrella.

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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

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(See) 211. Psathyrella polycephala (variant Smith 81000).
Pileus 2-4 cm broad, obtuse to convex expanding to nearly plane, margin
inrolled at first, surface glabrous, moist, hygrophanous, dark to medium honey
brown but fading to dingy buff or pallid (except where blackish from deposited
spores); veil rudimentary to absent, all traces soon vanishing.
Lamellae close, moderately broad, adnate, seceding, pallid to brownish when
young, blackish at maturity, edges even.
Stipe 4-8 cm long, 2-4 mm thick, equal, fragile-cartilaginous, whitish and
bound into clusters at base by whitish mycelium, whitish overall fresh or dried
except where dusted by spores, surface unpolished, veil rudimentary and not
leaving readily distinct traces.
Spores 6.5-7.5 x 4-4.5 ju, smooth, lacking a distinct apical pore; shape in face
view elliptic to ovate, in profile subelliptic to obscurely inequilateral, color in KOH
dark chocolate color slowly becoming medium to pale chocolate color, in Melzer's
reddish rusty brown.
Basidia 4-spored, 6-7 IL wide, hymenium pale bister in thick sections revived
in KOH but fading on standing. Pleurocystidia scattered, 38-52 x 9-15 p, fusoidventricose with obtuse apex or varying to subcylindric, hyaline in KOH when wellrevived, wall thickening present as a slight thickening in the apex, surface smooth.
Cheilocystidia similar to pleurocystidia or clavate, but some voluminous (up to
65 x 18 A), hyaline and smooth in KOH.
Gill trama of interwoven hyphae having inflated cells, hyaline in KOH (or
near subhymenium pale bister as revived in KOH); subhymenium bister in KOH,
composed of small cells, color fading on standing in mounting medium. Pileus
cuticle of inflated cells 2-3 deep, some pyriform (but irregularly arranged); some
connective hyphae in region adjacent to cuticle with thickened brown walls at the
septa, remainder of trama hyaline. Clamps present.
Habit, habitat and distribution. Cespitose on elm logs, Cedar Lake, Washtenaw County, Michigan, Oct. 17, 1971, Florence Hoseney (Smith 81000).
Observations. The spore deposit as obtained on the surrounding leaves and the
caps of basidiocarps in the clusters is nearly black yet in KOH the spores fade
slowly to being only moderately dark colored. The gills at maturity are also
blackish. The large cheilocystidia are in bunches or small areas along the edge
of mature gills. The cystidia are not truly typical of Homophron yet the collection
is unquestionably very close to P. cernua and P. saccarinophila. It is placed in
P. polycephala temporarily at least because the gills finally become blackish and
broad. It has the spore size of P. saccarinophila.
408. Psathyrella populorum Trueblood & A. H. Smith, sp. nov.
Pileus 3-5 cm latus, obtusus demum convexus vel subplanus, aquose cinnamomeus, deinde pallide subochraceus; contextus sordide brunneus, fragilis; lamellae pallidae demum vinaceo-brunneae, latae, subdistantes, adnatae; stipes 3-7 cm
longus, 3-8 mm crassus, pallidus, ad basin sordidus, glaber, sursum pruinosus;
sporae 8-9.5 x 5-6 v; pleurocystidia 38-65 x 10-18 /A, fusoide ventricosa; tenuiter
tunicata vel crassotunicata. Typus. E. Trueblood 4485 (MICH); legit Juniper
Mountain, Owyhee County, Idaho, 9 June, 1971; subcaespitosa prope Populus
tremuloides.
Pileus 3-5 cm broad, obtuse to convex, the margin curved in somewhat,
expanding to plane or with a low umbo, pale watery tan moist, fading to pale
buff or dingy pallid, in age often dingy cocoa-color as spores mature (color much