The North American species of Psathyrella.

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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

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4-4.5,; pleurocystidia nulla; solitaria. Typus: Smith 20541 (MICH), legit prope
Milford, Michigan.
Pileus 2-4 cm broad, broadly convex, expanding to plane or the margin wavy
to undulating at maturity, surface glabrous except for the appendiculate margin
(only mature to nearly mature pilei were available), hygrophanous, cream-buff
fading to whitish. Context relatively thick and firm, odor not distinctive.
Lamellae crowded, narrow, adnate, brownish soon becoming dark cocoa-color,
edges distinctly whitish and remaining so.
Stipe 4-5 cm long, 3-4.5 mm thick, equal down to a slight basal enlargement,
white, not discoloring, naked or apex faintly pruinose.
Spores 7-9 (-12) x 4-4.5 va, smooth, apical pore small but distinct and apex
truncate under oil, shape in face view oblong to narrowly elliptic (a few large
spores subfusoid), in profile oblong to narrowly and obscurely inequilateral, color
in KOH rich cocoa-color darkening to chocolate-brown, in KOH reddish tawny,
wall about 0.2 p thick.
Basidia 2- and 4-spored. Pleurocystidia absent. Cheilocystidia as in var.
candolleana. Pileus cuticle of vesiculose cells 1-3 deep, hyaline and thin-walled.
Trama of pileus cocoa-brown in KOH but soon fading to pallid. Clamp connections present.
Type locality. Milford, Michigan.
Habit and habitat. Solitary on sandy humus under brush, September.
Distribution. Michigan.
Observations. The normal spores are oblong and dark cocoa-brown in KOH.
The cocoa-brown trama as revived in KOH and the features of the spores are
the important characters of the variety. It is rather anomalous to find such a
weakly pigmented pileus with the trama giving this reaction in KOH. The
basidiocarps are relatively fleshy and firm compared to other North American
variants, and occur solitary to scattered, but these features may not prove
constant.
Material examined. Michigan: Hoseney 1524, Mazzer 6091; Patrick 1921;
Smith 20541 (Type), 20545.
Section Fragilissimae (Romagnesi) Singer, Lilloa 22: 446. 1951.
Drosophila sect. Fragilissimae Romagnesi, Bull. Soc. Linn. Lyon 12: 51-54. 1944.
As indicated in the key, the major feature of this section is the spore length,
but, generally speaking, the species placed here have stipes 3.5-6 mm thick or
more
Type. Psathyrella marcescibilis.
Key to the Species of Section Fragilissimae
1. Spores 6 ju or more wide in broadest view. 2
1. Spores 4.5-6 A wide. 5
2. Spores somewhat compressed laterally. 3
2. Spores terete in cross section. 4
3. Spores 10-13 X 7-8 X 8-10 jA; veil remnants present only along the margin of the
pileus. 52. P. longipes.
3. Spores 13-15 X 6-7 X 7-8.5 Au; veil remnants covering the pileus at first.
53. P. fragilissima.
4. Spores 12-15 X 6.5-8 f. 54. P. elwhaensis.
4. Spores 15-18 X 10-12 /h. 55. P. thomii.
5. Spores 9-11 X 5-6.5 /; hyphae of subcuticular region of pileus heavily incrusted;
caulocystidia much inflated (to 30 A). 56. P. incrustans.