TYLOPILUS HUMILIS Thiers, Mycologia 58:815. 1966

Illustrations: See Microfiche No. 52

Pileus 5-12 cm broad at maturity, convex to subglobose when young, becoming broadly convex to plano-convex to highly irregular with age, frequently with an undulating or convoluted margin, often not appearing fully expanded at maturity; surface dry, but sometimes viscid to subviscid in wet weather, dull to rarely shining or glistening when old, velutinous to subtomentose, often appearing matted-tomentose when mature, sometimes becoming areolate with age; color brown ("cinnamon-brown" to "Prout's brown" to "snuff brown" to "Verona brown" to "Saccardo's umber") during all stages of development; margin sterile, entire, incurved, unchanging or becoming decurved with age. Context 1-2 cm thick on the disc, firm, white to whitish, staining pale vinaceous ("avellaneous") when exposed (irregular areas of blue discoloration observed in one collection). Taste and odor mild, not distinctive.

Tubes 5-10 mm long, depressed, often narrowly and shallowly so, white when young, becoming pale flesh color ("tilleul buff" to pale "salmon-color" to "seashell pink" to "pinkish vinaceous"); pores one to two per millimeter, angular, concolorous with the tubes, staining brown ("cinnamon brown" to "Prout's brown") when bruised.

Stipe 2-5 cm long, 0.5-3.5 cm thick at maturity, characteristically short and sometimes poorly developed, subbulbous to frequently equal except for an abrupt pinching or tapering at the base, sometimes eccentric, solid; surface dry, glabrous, smooth, except frequently reticulate at the very apex, white or whitish at the apex, unchanging or sometimes becoming pale vinaceous ("avellaneous") toward the base when old, staining brown ("cinnamon-brown" to "Prout's brown") when bruised. Context white, staining pale vinaceous ("avellaneous"), except sometimes yellow in outer layer near the base when exposed (irregular bluish areas observed in one collection).

Spore print dull reddish brown. Spores 8-12 X 3-4 Ám, hyaline in KOH, pale yellow in Melzer's, cylindric to subfusoid to subellipsoid, smooth, thin-walled.

Basidia 32-34 X 8-12 Ám, clavate, four-spored, hyaline in KOH. Hymenium staining brown in KOH. Hymenial cystidia 30-66 X 7-12 Ám, scattered to abundant, hyaline to yellow to occasionally dark brown in KOH, color sometimes fading, not incrusted, embedded in the hymenium, subcylindric to subfusoid to fusoid to fusoid-ventricose to clavate or mucronate with elongated apices.

Tube trama hyaline in KOH, strongly divergent from a distinct mediostratum that stains pale brown in KOH. Pileus trama homogeneous, interwoven. Pileus cuticle differentiated as a very thin layer of interwoven to appressed, nonincrusted hyphae that stain brown in KOH, underlain by a layer, 150-250 Ám thick, of gelatinous to subgelatinous hyphae. Stipe cuticle differentiated as a layer of clavate cells, 20-35 X 6-10 Ám, that stain brown in KOH, with scattered caulocystida 33-52 X 9-15 Ám that are typically mucronate with tapering, subacute apices, staining dark brown in KOH, with a layer of hyaline, gelatinous to subgelatinous, interwoven hyphae underneath. Clamp connections absent.

Chemical reactions KOH-cuticle black; NH40H-cuticle red; HCL cuticle pink; HN03-context negative to pale pink, cuticle bright pink to red; sulfoformalin-cuticle bright pink; guaiac-context dark blue; FeS04-context gray to green.

Habit, habitat, and distribution Solitary to gregarious to cespitose in a mixture of Bishop and beach pine. Fruiting only during the late fall and early winter season. This bolete certainly is one of the rarest of all the California species. It is known only from a single open grove of pines covering not more than half an acre in the vicinity of the now destroyed old dormitory of the fire station in Jackson State Forest east of Mendocino.

Material studied Mendocino County: Thiers 8391, 8815, 9009, 9067, 9290, 9333, 9347, 9437, 9687, 9813, 10582, 10594, 11053, 14157, 14599, 21276.

Observations The most unusual feature of this species is the apparent trend toward becoming gastroid. The stipe is frequently poorly developed and eccentric, and the tubes are sometimes permanently covered by the cuticle of the pileus. Furthermore, the basidiocarps often remain below ground until full maturity and some become only partially exposed. However, T. humilis is not a true puffball, since the spores are forcibly discharged.

Edibility unknown.

The Boletes of California
Copyright © 1975 by Dr. Harry D. Thiers
Additional content for the online edition © 1998 by Michael Wood, Fred Stevens, & Michael Boom
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