Description: Habit collybioid; fruit body size rather variable, depending on substrate quality and environmental conditions (Figs. 2 and 3). Pileus 1.5–7(9) cm diam., rarely larger, broadly convex to plane when mature, often also almost hemispheric and not umbonate, sometimes slightly depressed in the centre, with a straight margin, sometimes slightly incurved, only rarely somewhat wavy, sometimes with a striate margin in mature specimens when moist (striations con- tinue one fifth to half of the way to the pileus centre); surface smooth, viscid when moist, with a separable gelatinous pellicle, hygrophanous, pale orange brown or caramel brown when moist, fading to a light yellowish buff as it dries; staining blue when damaged or sometimes in response to environmental conditions. L a m e l l a e adnate to sinuate, cream to pale gray brown when young, dark purple brown mature, margin pale to whitish. S p o r e p r i n t dark violet brown to dark tobacco brown. S t i p e 4–7(9) × 0.2–0.7 cm, cylindrical, hollow, rather firm, apex pruinose, slightly enlarged at base, with thick white rhizomorphs; surface smooth to silky fibrillose, whitish when young and strongly bluing when bruised, later off- white and/or with yellowish shades. M y c e l i u m white, rhizomorphic, sometimes staining sky blue, odour and taste farinaceous. V e i l present in young specimens, cortinate, snow-white, later disappearing. Like P. azurescens or P. serbica var. moravica, a cortinate zone can be present and coloured purplish brown by spores. F l e s h tan, staining blue when damaged, odour and taste strongly farina-ceous.
Basidia cylindrical, mostly 27–37 × 9–11 μm, 4-spored, sterigmata usually 4–5.5 μm long. Clamp connections abundant. Spores (11.1)12.0–12.6–13.1(14.2) × (6.5)6.8–7.1–7.4(7.9) μm, Q = 1.6–1.8–1.9; slightly nar- rower in side view (median ~ 6.8 μm), elongate-ellipsoid, equilateral in face view, somewhat inequilateral in side view, with an apical pore, relatively thick-walled (0.8–1 μm), brownish with a yellow tinge in 5% KOH (Fig. 4C). Cheilocystidia abundant, variable in shape, narrowly clavate-mucronate, narrowly lageniform (neck no longer than 8 μm), rarely with a forked neck, infrequently narrowly fusiform to fusiform, hyaline, thin-walled, mostly 20–30 × 6–8 μm (Fig. 4A). P l e u r o c y s t i d i a common, narrowly to broadly clavate-mucronate (rarely with subcapitate apex), hyaline, thin-walled, mostly 25–35 × 9–14 μm (Fig. 4B). Caulocystidia present, variable in shape but generally similar to cheilo– and pleurocystidia. All types of c y s t i d i a sometimes finely encrusted at apex.
Habitat and phenology. Scattered to gregarious, sometimes caespitose, growing on woody debris, usually on wood chips (Pinus radiata, Cupressus macrocarpa, Eucalyptus, Pseudotsuga menziesii, Alnus and others). Synan- thropic, most common in urban wood chip landscaping and also found in wood chipped gardens, parks and similar urban locations. This species is easy to cultivate on agar, grain spawn, and sawdust or wood chips. Fructifies in cold weather, from late September to January.
Distribution. Known from Los Angeles (CA, USA) to Seattle (WA, USA). This species is not as common in coastal dune grasses as its close relative P. cyanescens, though it does occur there in Northern California. While most col- lections have been found in the San Francisco Bay Area and Humboldt County (CA) within 10 miles of the ocean or bay, it has been found at least 100 miles inland in California.
Chemical analyses are not available. However, P. allenii is consumed for its hallucinogenic properties, and is commonly sought out by some mushroom hunters; it is roughly equivalent in potency to P. cyanescens.