Armillaria straminea (Krombholz) Kummer var. americana var. nov. f. americana

Agaricus stramineus Krombholz, Naturgetreue Abbildungen und Beschreibungen der essbaren, schadlichen und verdachtingen Schwamme; pl. 25, figs. 8-14, 1836. Illustrations: Fig. 3; Smith (1949) reel 32, no. 222, (1975) p. 143.

Pileus 4-18 cm latus, demum late umbonatus vel convexus siccus, sapor mitis; lamellae latae, adnatae, confertae, vel subdistantes, pallide lutae; stipes 5-12 cm longus, 1.2-2.5 cm crassus, saepe bulbosus (3 cm latus); vellum copiosum, floccosum; sporae in cumulo albae, (5) 6-8 x (3.7) 4-5 microns leviter amyloideae; trama lamellorum hyphis parallelis. Specimen typicum in Herbarium Denver Botanic Gardens conservatum est; legit prope West Village, Aspen, Colorado, 9 August 1975, Smith 85661 (DBG--6254).

 Pileus 4-18 cm broad, obtusely conic to convex, becoming broadly umbonate to plane, surface dry, with conspicuous triangular scales, appressed-fibrillose at first but scales becoming tufted and recurved in age (up to 1 cm broad with recurved tips to 0.5 cm long), imbricate, arranged in concentric circles, surface of cap glabrescent in age; ground color "straw yellow" and scales varying from "lemon chrome" to "mustard yellow" and finally at times with orange-brown tips, fading in sun to whitish; margin incurved at first, becoming straight, appendiculate with remnants of yellow floccose veil. Context white except stained bright yellow to depth of 3-4 mm under cuticle, firm, up to 3 cm thick, odor and taste mild, KOH and FeSO4 both negative.

Lamellae adnate to sinuate, moderately close, broad (to 12 cm), margins crisped and soon eroded to serrate, light yellow when young becoming pale lemon yellow in age, always lighter colored than pileus, not staining.

Stipe 5-12 cm long, 1.5-2.5 cm thick, equal to expanding upward but often with a bulb up to 3 cm thick; smooth and white above the thick floccose veil, soon shaggy squamulose below from veil remnants; the scales concolorous with pileus and up to 5 mm long, arranged in concentric zones below annular zone; base not discoloring, solid to loosely stuffed with white pith; cortex stained yellow to depth of 1 mm in area below annulus.

Spore deposit white. Spores (5) 6-8 x (3.7) 4-5 microns. Cystidia none. A few dextrinoid basidioles scattered in hymenium. Lamellar trama parallel, hyphae thin-walled, tubular, the cells 30-45 x 10-15 microns and rectangular in optical section. Clamps present. Cuticle of pileus of long filamentous hyphae untited in places into semi-erect fascicles, cells 80-150 x 8-15 microns, vey little constriction at cross-walls, clamps infrequent. Yellow pigment soluable in alcohol, water, and KOH and soon breaking down where exposed to sunlight.

Habit, habitat and distribution: In aspen groves with scattered alder and maple, common most years at elevations of 7,000 to 9,000 feet during the summer rainy period.

Observations: No collections were found that showed any integradation with A. albolanaripes but Miller's (1972) pl. 107 may be such a variant.

Material cited: COLORADO: Barrill 18; Hesler 12684; Mitchel 1307 (A), 2430, 2803, 3794, 4116, 5111, 5300, 5949, 5950, 5974, 5975, 6129, 6130; Smith 85140, 85847. WASHINGTON: Smith 31216. WYOMING: Solheim 3522, 3558.