Photo: Sharmin Gamiet
Russula occidentalis
Singer

Pileus: 5.5 - 11 cm broad; convex when young, becoming planar and finally depressed at maturity; margins inrolled at first, becoming straight and even, finally uplifted, at times eroded, striate; surface dry to viscid, smooth, unpolished when weather is dry, but can be polished, peeling readily till disc; colour variable, ranges from olive yellow to dark green to reddish brown; olive, violet brown, dark ruby, dark to greyish green on disc, paler or with yellow tones towards margins; context 0.3 - 1.0 cm at junction of stipe, fleshy to spongy, colour white to brownish grey, slowly bruising red then finally black; taste mild; odour indistinct to variously described as ‘wine-like’, ‘fermenting-like’.

Lamellae: Ascending at first then horizontal to notched, at first close then average to distantly spaced, ‘fat’, forking at stipe; colour white at first, becoming yellow at maturity; no lamellulae.

Stipe: 4.0 - 11.0 cm long X 2.0 - 3.5 cm wide at apex, 1.5 - 3.0 cm wide at base, tapering downward or equal; surface dry, unpolished, fibrous, often with grooves or striations; colour white bruising red at first then black; context solid, spongy, with a thick rind, white to pallid, then yellow, bruising grey black at times without turning red first. Turning red with application of PDAB.

Microcharacteristics: Spore print yellow; spores 9.6 - 14.1 X 7.4 - 11.8 µm, subglobose to broadly ellipsoid, with amyloid warts; with abundant hymenial cystidia.

Comments: In these forests, this species can be confused with R. aeruginea, or R. xerampelina. R. occidentalis is separated from these 2 species because R. occidentalis turns red then black when bruised while the other 2 species do not. R. aeruginea does not show any colour changes, while R. xerampelina may show some yellow to yellow brown when bruised. Tissue of R. occidentalis will turn bright red with PDAB, in the other species it will not .

Further Reading:

Arora, D. 1986. Mushrooms Demystified. Ten Speed Press. Berkeley, Ca. pp 958.
Thiers, H.D. 1997. The Agaricales (gilled fungi) of California. 10. Russulaceae I. Russula. Mad River Press. Eureka Ca. pp 158.