Summary:
Features include 1) a dark brown to reddish brown or orange-brown cap with a slightly viscid, matted-fibrillose, streaked or floccose surface, 2) adnate to notched, close, narrow gills that are pale yellow or yellow, staining reddish brown, 3) a fairly long, dry, whitish to reddish brown stem that is bald to somewhat fibrillose, and 4) farinaceous odor and taste. According to Bessette(5) this species is treated as Tricholoma nictitans in Shanks(2) and Ovrebo(5). Shanks(2) gives the range of T. nictitans in CA as Mendocino County northward, but the name T. nictitans has been abandoned by most European mycologists (Bessette(5)). T. nictitans is synonymized with T. fulvum (DC.) Bigeard & H. Guill. in the online Species Fungorum accessed May. 4, 2016. Breitenbach(3) give the same synonymy for T. fulvum (DC: Fr.)Sacc. but say (with Latin names italicized), "Authors with a narrow species concept [of Tricholoma fulvum] distinguish two species within the one described here: Tricholoma fulvum, an obligate mycorrhizal partner of Betula, with pronouncedly yellow lamellae and yellow stipe flesh along with a ribbed pileal margin; and T. nictitans, under conifers or in mixed forests without birches, with scarcely to slightly yellow lamellae, and with a smooth pileal margin. Microscopic differences are not significant." Shanks(2), on the other hand says that the "European species" T. fulvum has yellow gills and stem apex, spores measuring 5-6.5 x 3.5-4.5 microns, and hyphae of the stem surface that are gelatinized, whereas the gills of T. nictitans are yellowish white to cream and spores measure 5.3-8.2 x 3.4-6.2 microns. Ovrebo(5) says of the T. transmutans concept, italicizing the Latin names, "A species of questionable concept that is related to T. fulvum is Tricholoma transmutans Peck. As pointed out by Ammirati and Ovrebo (1979) its relationship to T. fulvum (and T. pessundatum) is hard to establish because the color of the lamellae is difficult to interpret. Peck described them as being whitish or pale yellow. A plate in a later publication (Peck, 1896) shows the lamellae as yellow in face view but white or light buff when viewed as a group from an oblique angle. Peck''s description does not suggest that the lamellae changed color during maturation either."

Cap:
2.5-11cm across, conic becoming convex or nearly flat, often with low, broad umbo, margin inrolled, remaining so or becoming downturned or straight; "dark brown to reddish brown" with paler, sometimes striate margin; "slightly viscid then dry, with densely matted fibrils over the disc", (Bessette), 5-8cm across, convex, then expanded and umbonate; brown, fulvous, or chestnut, often with a reddish brown umbo, but yellowish brown closer to the margin; finely virgate or floccose, (McNeil), 5-7.5cm across, convex; alutaceous when moist, becoming brownish or reddish brown when dry; smooth, very viscid or glutinous when moist, (Peck)

Flesh:
white to buff, (Bessette), firm; white, yellow under cap surface, (McNeil)

Gills:
"adnate to emarginate or nearly free, close, thin"; "yellowish white to buff", "faces becoming spotted or edge entirely reddish", (Bessette), adnate, then sinuate-emarginate, close, narrow, cream, pale yellow or yellow, staining reddish brown, sometimes becoming pale yellow at maturity, (McNeil), close, narrow, some branched; "whitish or pale yellow, becoming spotted with reddish stains", (Peck)

Stem:
4-15cm x 0.7-2cm, equal or slightly clavate [club-shaped], solid or hollow, "often long relative to the cap diameter and slightly rooting"; "yellowish buff to grayish orange", dull reddish brown toward the base when mature; "dry, appressed-fibrillose, with occasionally projecting fibrils", pruinose at top, (Bessette), 6-15cm x 1-2cm, equal, tapering toward the base, often somewhat rooting, solid or hollow; whitish or reddish; bald or somewhat fibrillose, staining reddish brown with maturity or bruising, (McNeil), "equal or slightly tapering upwards", "stuffed or hollow"; "whitish, often marked with reddish stains"; smooth, (Peck)

Odor:
farinaceous (Bessette, McNeil)

Taste:
farinaceous (Bessette), unpleasant (McNeil)

Microscopic spores:
spores 5-8.6 x 3.4-6.2 microns, elliptic, (Bessette), spores 6-7.5 x 4-5 microns, elliptic, smooth, colorless, (McNeil), spores 5 microns, nearly round, (Peck), spores 5.3-8.2 x 3.4-6.2 microns (Shanks(2) for T. nictitans)

Spore deposit:
white (McNeil)

Notes:
Tricholoma transmutans is said to be the most common Tricholoma species in QC, and also occurs on the West Coast including BC (Bessette(5) who show photographs from BC, QC, and NS). There are two collections of T. transmutans from WA at the University of Washington and one collection from OR at the New York Botanical Garden.

EDIBILITY

unknown, but similar species are poisonous (Bessette(5)), yes, but poor (McNeil(1))