Illustrations: See Microfiche No. 14

Pileus 6-12 cm latus, convexus vel planus, humidus vel subviscidus, valde reticulatus vel rugosus, disco brunneus, margine bubalinus. Contextus albus, immutabilis. Sapor et odor mitis. Tubuli 0.5-1 cm longi, albi demum flavi, tactu immutabiles. Stipes 5-7.5 cm longus, 1.5-3 cm crassus, aequalis vel subclavatus, siccus, reticulatus, bubalinus. Sporae 14.3-17.1 X 3.8-5.2 Ám, laeves, cylindricae vel subellipsoideae, inaequilaterae. Cystidia nulla. Cuticula intertexta, cellulis terminalibus hypharum ovoideis vel clavatis. Holotypus (Thiers, No. 30502) a Mrs. Lillian Mott lectus prope Grass Valley, Nevada County, November 6, 1972; in Herbarium San Francisco State University conservatus.

Pileus 6-12 cm broad, convex when young, typically becoming plane to plano-convex to shallowly and broadly depressed on the disc at maturity; surface moist to subviscid, conspicuously wrinkled-reticulate over entire surface during all stages of development, the reticulum noticeably raised on the disc, but sometimes becoming shallower and may eventually appear as appressed fibrillose scales on the very margin; the reticulations remain very pronounced on dried pilei and are usually darker than the intervening areas; color brown ("cinnamon" to "cinnamon brown") on the disc, fading to buff ("antimony yellow" to "warm buff" to "light buff" to "light ochraceous buff") toward the margin; margin incurved to decurved, entire. Context 1-2 cm thick, soft, white, unchanging when exposed. Taste and odor not distinctive.

Tubes 0.5-1 cm long, depressed, white when young, becoming yellow to greenish yellow ("citrine yellow" to "reed yellow" to "olive yellow") at maturity, unchanging when bruised; pores up to 1 mm broad, angular concolorous with the tubes, unchanging when bruised.

Stipe 5-7.5 cm long, 1.5-3 cm thick at the apex, equal to subclavate, solid; surface dry, finely reticulate over entire surface, reticulations suggestive of those of B. edulis but more delicate; background color buff to pinkish buff ("pinkish buff" to "pale pinkish cinnamon" to "pinkish cinnamon") during all stages of development; reticulations concolorous with the surface. Context white, unchanging upon bruising or exposure.

Spore print color unknown. Spores 14.3-17.1 X 3.8-5.2 Ám, pale ochraceous in KOH, slightly darker in Melzer's, cylindric to subellipsoid in face view, ventricose and inequilateral in profile, walls smooth, thin; some pleomorphic spores present.

Basidia 23-30 X 7-10 Ám, clavate, two- and four-spored, hyaline in KOH. Hymenial cystidia not seen (cystidia possibly present, but not reviving in KOH).

Tube trama parallel to only slightly divergent, narrow, laticifers sometimes present, hyphae 3-5 Ám wide, cross walls prominent but inamyloid. Pileus trama homogeneous, interwoven, hyphae 5-7 Ám wide, cross walls inamyloid. Pileus cuticle subgelatinous, up to 500 Ám broad, well differentiated as a somewhat tangled to suberect trichodermium, hyaline in KOH, not staining in Melzer's, terminal hyphae septate with terminal cells ovoid to clavate, 20-40 X 10-20 Ám, subterminal cells more elongate to ellipsoid, walls sometimes incrusted, cross walls inamyloid, hyphae 3-7 Ám wide. Stipe cuticle differentiated as a layer of fertile basidia with scattered, fusoid to clavate to fusoid-ventricose caulocystidia. Clamp connections not seen.

Chemical reactions negative.

Habit, habitat, and distribution Known only from the vicinity of Grass Valley and Nevada City, where it has been found under conifers.

Material studied Nevada County: Thiers 30503 (collection made by Lillian Mott) type.

Observations This species appears most closely related to B. edulis and other members of that species complex. The strongly reticulated or ridged surface of the pileus readily distinguishes it, however, from any member of that group. The color of the pileus is also different, and the reticulum on the stipe appears much more delicate than that usually associated with B. edulis. The only other species known from California in which the surface of the pileus is even remotely suggestive of B. mottii is B. fibrillosus, but that species has yellow tubes when young, a rather elongated stipe, and a much darker colored pileus.

Edibility undetermined.

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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