Cap 4.0-8.0 cm broad, convex, broadly so in age; margin incurved, then decurved, often wavy; surface dry, the disc pale-tan, glabrous to areolate, elsewhere appressed-fibrillose, the fibrils whitish over a dull, bluish-green background; context firm, pallid, streaked bluish-green,1.0-2.0 cm thick at the disc, rapidly thinning towards the margin; odor when young, strongly of "mushrooms," unpleasant at maturity; taste slightly astringent, disagreeable.
Gills adnate to subdecurrent, close, relatively thick, dull bluish-grey; lamellulae in three to four tiers.
Stipe 3.0-5.0 cm long,1.0-2.5 cm thick, solid, equal, sometimes with a pointed base, the latter immersed in whitish mycelium; surface dry, appressed fibrillose-striate, the fibrils whitish, darkening with handling, over a dull, bluish-green ground color; context whitish, firm, streaked bluish-grey like the cap context; partial veil absent.
Spores 6.5-8.5 x 4.5-5.0 µm, elliptical in face-view, similar in profile, slightly inequilateral, smooth, thin-walled, hilar appendage conspicuous, inamyloid; spores white in deposit.
Solitary or in small groups in conifer duff at mid-elevations of the Sierra Nevada; fruiting in the spring; rare in most years, occasional in wet seasons.
Unknown; an unpleasant odor at maturity is a deterrent.
Hygrophorus caeruleus is a rare montane species recognized by a bluish-green to bluish-grey color, unpleasant odor, and spring fruiting habit. Its stature is suggestive of Tricholoma or Russula, but the gills are not notched, as is often the case in Tricholoma, nor is the stipe brittle or breaks cleanly as in Russula. Unrelated, similar colored taxa include Clitocybe odora, Stropharia aeruginosa, Stropharia cyanea, and Entoloma bloxami. Clitocybe odora differs in its less robust stature, whitish stipe, and pleasant anise odor, while Stropharia aeruginosa and Stropharia cyanea have viscid caps, brownish gills in age, and lack a strong odor. Entoloma bloxami has a dark-blue cap and sometimes a bluish-tinged stipe. It occurs primarily in coastal forests in the fall and winter and can be distinguished by a pinkish spore print.