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Species Information
Summary: Subgenus Russularia. Features include 1) a moist, striate cap that is brown to dark brown, 2) white to whey-like milk that is unchanging but stains white paper yellow, 3) close, narrow, light orange gills that bruise reddish brown, 4) a stem colored as the cap or lighter, 5) a mild taste, 6) association with alder, 7) a white spore deposit, and 8) elliptic spores with amyloid warts, spines and ridges. The description is derived from Hesler(4) except where noted.
Collections were cited from WA, OR, and CA, (Hesler(4)). There are collections from BC, WA, and OR at the University of British Columbia and collections from WA and AK at the University of Washington.
Cap: 1-3.5cm across, depressed or sometimes with a papilla, margin decurved [downcurved] first then spreading or uplifting to a shallow funnel; olive-brown to fuscous then tawny to cinnamon or dark vinaceous brown; moist, not viscid, opaque then translucent-striate by maturity, often rugulose [wrinkled] or pitted, (Hesler), "olive-brown to brown-gray then tawny to dark pink-purplish brown", (Leuthy)
Flesh: thin, fragile; buff or toward cinnamon, in stem slowly reddish brown where cut, MILK "white to whey-like, usually soon changing to yellow on exposure to air, but at least staining white paper yellow", (Hesler), "white to whey-like, unchanging, slowly staining field labels pale yellow", (Methven), white to whey-like, may be scanty or absent, (Trudell)
Gills: "adnate or decurrent by lines, close, narrow"; "light pinkish cinnamon" to "pinkish cinnamon", slowly incarnate-tan where broken, often reddish tan when old; edges even, (Hesler), pinkish cinnamon to pinkish tan, (Trudell)
Stem: 3-6cm x 0.5-0.6cm, evenly enlarged downward or equal, solid; "sepia" or paler, the top paler than lower part; smooth, bald, unpolished, (Hesler), color as cap or lighter, (Leuthy)
Odor: none or slight
Microscopic spores: spores 8-10 x 6.5-8 microns, elliptic, reticulum of [presumably amyloid] warts and spines connected by amyloid lines forming nodulose [bumpy] ridges, "not infrequently with short branches and with fine lines connecting to the larger nodules but not forming a reticulum, some isolated warts present, with or without fine tails", prominences 0.2-0.6(0.8) microns high; basidia 4-spored, 31-42 x 8-10 microns, nearly colorless in KOH; pleurocystidia: macrocystidia 60-92 x 8-12 microns, "ventricose-acuminate or fusoid, walls thin", pseudocystidia 2-4 microns wide, filamentous to narrowly clavate, cheilocystidia 26-38 x 4-8 microns, similar to pleurocystidia; cap trama "brownish in KOH and heteromerous, the sphaerocysts rather small", (Hesler), spores 8-9.5(10) x 6-7 microns (Methven)
Spore deposit: white
Habitat / Range
scattered under Alnus (alder) and Thuja, (Hesler), scattered in duff, in coastal coniferous-deciduous forests in association with Alnus (alder), (Methven for California), summer, fall
Similar Species
Lactarius obscuratus var. obscuratus has an olive brown cap, lacks the yellow staining reaction of the milk on white field labels, has a distinctly peppery taste, and has smaller spores (6-7.5 x 5-6.5 microns), (Methven, who calls it a European species). The association with alder and the presence of rosettes of sphaerocysts in the cap and stem trama are useful in differentiating Lactarius occidentalis from other small Lactarius species with similar colors. Lactarius carbonicola has milk that is not whey-like, taste is slightly peppery, and the colors are "those of the vinaceous-red series of Ridgway", (Hesler(4)). See also SIMILAR section of Lactarius obscuratus var. radiatus.
