Summary:
Features include a cap that is often a shade of brown and having a margin that is inrolled for a long time, staining of all parts brown to reddish brown when handled or when old, decurrent gills that are forked or veined near stem, a stem shorter than the cap width, and sometimes association with birch. Paxillus involutus group is commonly found in the Pacific Northwest and several species are involved. |The group designation is used because Paxillus involutus is a genetic complex of at least four species. This was worked out as recorded in Hedh(1), Vellinga(22), Gelardi(1), and Jargeat(1). |The species are Paxillus ammoniavirescens Contu & Dessì (= Paxillus validus), Paxillus obscurisporus C. Hahn, Paxillus cuprinus Jargeat, Gryta, J.-P. Chaumeton & Vizzini, and Paxillus involutus sensu stricto. A key in Jargeat(1) differentiates them as follows (spore characters are omitted here). |Paxillus ammoniavirescens has a green reaction on the cap with concentrated ammonia especially on the slimy part, unlike the other species in the complex. It is usually also more brightly colored with yellow, orange or fulvous shades than the others and more slimy. The spore print is usually greenish-tinged. (Jargeat(1), p. 28). |Paxillus obscurisporus has a fairly large cap up to 30cm across and often grows in clusters. The fresh spore print is deep reddish brown to vinaceous brown. (The couplet of Paxillus involutus and Paxillus cuprinus have a cap up to 12(20)cm across, grow scattered or connate in 2s or 3s, and the spore print is lighter, ochraceous with a reddish shade.) (Jargeat(1), p. 28). |Paxillus cuprinus is a species associated with birch and other Betulaceae (growing in bright places, both urban areas and natural sites), described from Europe in 2014. The cap has an olivaceous shade when young and coppery brown or reddish brown when old. (Jargeat(1), p. 28). |Paxillus involutus grows in forests, typically in shady areas. It grows with a wide range of conifers and hardwoods. The cap is often umbonate with variable colours: gray-brown, rusty brown, ochraceous brown, olivaceous brown, or sometimes whitish. (Jargeat(1), p. 28).

Cap:
4-15(20)cm across, at first broadly convex with strongly inrolled margin, then flat or centrally depressed with margin eventually unfurled; brown to dingy yellow-brown, olive-brown, or dingy reddish brown, often with darker brown stains; "viscid when moist but otherwise dry", "smooth or with soft matted hairs that wear away", sometimes cracked (areolate) when old, "margin often slightly velvety or obscurely ribbed", (Arora), 4-15cm across, convex becoming flat with a central depression when old, margin deeply inrolled at first, remaining inrolled until a late age; cap "light reddish brown, tinged with olive, to yellow-brown"; dry, "covered with matted, soft hairs, sometimes obscurely zoned or spotted", (Miller)

Flesh:
thick, firm; "pale buff to yellowish, but usually staining reddish to brown when cut", (Arora), thick; dingy yellowish bruising brownish, (Miller)

Gills:
"usually decurrent, close or crowded", often forking and/or forming pores (anastomosing) near stem; "pallid to pale yellowish becoming dingy yellow to olive, brownish, or yellow-brown", staining dark brown or reddish brown when bruised or when old, (Arora), decurrent, crowded, broad, sometimes anastomosing and interveined near stem; yellowish olive bruising brown, (Miller)

Stem:
2-7(10)cm x 0.5-4cm, "usually shorter than width of mature cap, equal or tapered at either end, central to somewhat off-center, solid, firm"; cap-colored or paler, "often with dingy reddish to dark brown stains"; dry, smooth, (Arora), 4-10cm x 1.4-2cm, equal or widening downward, central; "yellowish brown, streaked or stained darker brown"; dry, bald, (Miller)

Veil:
absent (Arora)

Odor:
mushroomy (Phillips), pleasantly aromatic, fruity, (Breitenbach), slightly acid-fruity (Lincoff(1)), pleasant (Miller)

Taste:
acid (Phillips), mild, sourish, fungoid, sometimes astringent, (Breitenbach), mild to unpleasant (Miller)

Microscopic spores:
spores 7-10 x 4-6 microns, elliptic, smooth, (Arora), spores 7-9 x 4-6 microns, elliptic, smooth, yellowish to dextrinoid in Melzer''s reagent, thick-walled, (Miller), spores 6.6-10.2 x 5.1-6.7 microns, elliptic-oval, smooth, iodine-negative; basidia 4-spored, 30-48 x 8.5-10.5 microns, clavate, with basal clamp connection; pleurocystidia and cheilocystidia 40-90 x 8-15 microns, fusiform, with brown contents; clamp connections mentioned for basidia and cap cuticle, (Breitenbach)

Spore deposit:
brown to yellow-brown, (Arora), rust-brown (Breitenbach), clay-brown to yellowish brown (Miller)

Notes:
Jargeat(1) listed the distribution of Paxillus involutus sensu stricto as "Present all over Europe (France, Belgium, Great Britain, The Netherlands, Sweden, Norway, Czech Republic) and in North America (Canada and the USA)." There is genetic evidence in BC of four different species which could align with the four known species in the complex: morphological correlation is required, (D. Miller, pers. comm.). There is also some genetic evidence of Paxillus cuprinus in WA and OR (D. Miller, pers. comm.). Paxillus cuprinus occurs in WA, CA, France (including holotype), Germany, Italy, Sweden, and Iran (Jargeat(1) with original description). Siegel(2) reported and illustrated Paxillus cuprinus from CA and mentions that there are 2 similar undescribed species in CA. There are collections labeled Paxillus involutus from BC at the University of British Columbia, and collections labeled Paxillus involutus at the University of Washington from WA, OR, CA, NB, ON, AK, CO, MI, and NY.

EDIBILITY

poisonous: can cause hemolysis and kidney failure (Arora), severe gastrointestinal upset can result (Miller)