The veiled species of Hebeloma in the western United States / Alexander H. Smith, Vera Stucky Evenson, and Duane H. Mitchel.

The Subgenus Hebeloma

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pointed base, stuffed becoming hollow with a distinct white copious
cortina in button stages, brunnescent (+ bister) in age, near apex
white-pruinose, surface below apex ~ appressed white-fibrillose from
veil remnants; base with white rhizomorphs.
Spore deposit "Vinaceous-Cinnamon." Spores (7.5) 8.5-11.5 x
5.5-6 iLm, ovoid to ellipsoid, apex rounded, smooth in KOH and pale
yellow, not dextrinoid, smooth at 7,000 x magnification with SEM.
Hymenium.-Basidia 4-spored, 22-26 x 6-7 pjm. Pleurocystidia
none. Cheilocystidia 34-49 x 5-9 [mm, + fusoid-ventricose, apex obtuse, internally with clumped refractive material, orange-yellow in
KOH when fresh and somewhat resembling that of chrysocystidia.
Lamellar and pilear tissues.-Lamellar trama typical of the genus. Cuticle of pileus a thin ixocutis, the hyphae clamped, yellowish
and 3-5 (xm diam, encrusted refractive pigment present on the walls.
Hypodermium intermediate (both cellular and hyphoid elements present), yellowish in KOH in fresh material. Pileus trama compactly
interwoven, yellowish to hyaline in KOH, the cells often greatly
inflated.
Habit, habitat, and distribution.-Gregarious under young cottonwoods on litter in an old granite pit, Poorman Gravel Pit, Sunshine,
Boulder County, Colorado, May 22, 1979, legit Vera Evenson (type,
DBG).
Observations.-The stature, raphanoid odor and taste, and the
color of the mature gills indicate the genus Hebeloma, but the cheilocystidia are aberrant insofar as their content is concerned, and the
color of the spore deposit is not typical of the genus. It is, however
within the range we have found for the genus. The pale yellow color of
the spores in KOH is a feature not infrequently encountered in other
species of the genus, and the absence of ornamentation on the spores
as seen in SEM studies (pl. 9) is not typical of the genus. Ricken
(1915) described cheilocystidia with a yellow content for Hebeloma
punctatum. The cheilocystidia of H. evensoniae, however, are larger
and not threadlike, the stipe base slowly becomes very dark brown,
and the spores are not exceptionally thick-walled for the genus.
Stirps CHAPMANAE
Spores narrow, 3.5-5 Rm wide; taste bitter.
9. Hebeloma chapmanae sp. nov.
Pileus + 3 cm latus, plano-convexus, saepe umbonatus, glabrescens, subviscidus, argillaceus vel ochraceus ad marginem, ad centrum