LECCINUM ARBUTICOLA sp. nov.

Illustrations: See Microfiche No. 27

Pileus 7-10.5 cm latus, viscidus, glaber vel subtomentosus, brunneus vel ferrugineus, tactu caerulescens. Contextus albus, tactu testaceus demum fuscus vel nigrescens. Sapor et odor mitis. Tubuli usque 1.5 cm longi, brunnei demum bubalini; pori 0.5-1 mm lati, tactu olivaceo-brunnei. Stipes 9-13 cm longus, 1-3.5 cm crassus, aequalis, solidus, albus, squamis albis demum fuscis. Contextus stipitis albus, tactu apice pileo similis et basi caerulescens. Sporae 15-17.1 X 4.5-5.8 µm, ellipsoideae vel subcylindricae. Cystidia 41-46 X 9-11 µm, hyalina, fusoideo-ventricosa, dispersa vel rara. Cuticula intertexta, cellulis elongatis, incrustatis, globulis pigmenti nullis. Caulocystidia fasciculata, clavata, brunnea in KOH. Holotypus (no. 30514) a H. D. Thiers lectus prope Nevada City, Nevada County, November 11, 1972; in Herbarium San Francisco State University conservatus.

Pileus 7-10.5 cm broad, obtusely convex to convex when young, typically becoming plano-convex to occasionally convex with an incurved or decurved margin with age, occasionally with shallow depressions on the disc; surface viscid (at least in wet weather), viscidity much more apparent in older basidiocarps and often only slightly viscid when young, glabrous to obscurely tomentose, no evidence of appressed fibrils or scales (as in L. manzanitae), staining blue when bruised, especially when young; color brown to rust brown ("cinnamon brown" to "ochraceous tawny" to "Dresden brown" to "buckthorn brown"), little indication of reddish pigments, evenly colored or somewhat paler toward the margin, with age fading to pale brown ("buckthorn brown") to tan ("warm buff" to "light buff"), when covered with leaves or debris tan to buff ("clay color" to "warm buff" to "light buff") with many paler areas ("pale olive buff") or almost white, occasionally with darker areas ("cinnamon buff" to "pale ochraceous buff"); margin sterile. Context 2-3 cm thick, white, changing to reddish before becoming fuscous, reddish stage often persisting and readily noticeable; eventually the fuscous color fades and context becomes pallid. Taste and odor not distinctive.

Tubes up to 1.5 cm long, adnate to depressed when young, becoming deeply and narrowly depressed with age; when young dark brown ("Dresden brown"), with age fading to buff ("pale olive buff" to "olive buff"), staining darker olive buff to lavender ("avellaneous" to "wood brown") when bruised; pores 0.5-1 mm broad, staining olive brown when bruised.

Stipe 9-13 cm long, 1-3.5 cm broad at the apex; typically equal, but sometimes enlarging toward the base, solid, whitish mycelium at the base; surface dry, with scattered scabrosites, which never form a conspicuous element on the surface; background color white but with a strong tendency to stain blue when bruised, color change immediate and suggestive of that of Gyroporus cyanescens; ornamentations white to pallid at first, typically becoming dark brown to fuscous, if covered with debris remaining pallid or white. Context white, staining as in pileus.

Spore print color unknown. Spores 15-17.1 X 4.5-5.8 µm, pale ochraceous to rarely dextrinoid in Melzer's, ochraceous in KOH, fusiform to subcylindric in face view, inequilateral in profile, walls smooth, thin.

Basidia 25-29 X 9-12 µm, one to four-spored, clavate, hyaline, often filled with conspicuous oil droplets. Hymenial cystidia 41-46 X 9-11 µm, rare to scattered, embedded in the hymenium, often inconspicuous, hyaline, thin walled, fusoid to fusoid-ventricose, often with an elongated and somewhat flexuous apex.

Tube trama hyaline, divergent from a distinct central strand, hyphae 5-6 µm wide. Pileus trama interwoven, hyaline in KOH, with scattered conspicuous laticifers, hyphae 5-7 µm wide. Pileus cuticle differentiated as a tangled trichodermium; orange yellow in ammonia, pale yellow in KOH and ochraceous in Melzer's; homogeneous, no pigment globules in Melzer's, some disarticulation, hyphae 8-12 µm wide, terminal cells elongated and with a tapered apex. Caulocystidia 25-36 X 7-10 um, clustered, clavate to rarely fusoid-ventricose, contents when older staining brown in KOH, some secondarily septate, occasionally fertile basidia and huge caulocystidia intermixed. Clamp connections absent.

Chemical reactions KOH-context of stipe yellow; NH₄OH-context of pileus yellow.

Habit, habitat, and distribution Scattered to gregarious under madrone (Arbutus menziesii), often completely covered with leaves and debris. Known only from lower elevations of the Sierra Nevada in the vicinity of Grass Valley and Nevada City.

Material studied Nevada County: Thiers 30512, 30513, 30514 type, 30519, 30520.

Observations This is another addition to the ever-increasing number of Leccinums associated with members of the Ericaceae (manzanita, madrone, etc.). It is readily distinguished from the other species associated with these trees by the brown to buff color of the pileus, the distinct reddish stage in the sequence of color changes in the flesh with the eventual return of the context to almost white after prolonged exposure, and the strong blue discoloration developing in the basidiocarp when bruised. The absence of pigment globules in the cuticular hyphae in Melzer's reagent further differentiates it from L. manzanitae.

Edibility undetermined.