Appearance
Fully grown, the cap can range from 7 to 30 cm in diameter, whitish to dull-yellow, and is funnel-shaped with a central depression. The gills are narrow and thin, decurrent in attachment, nearly white when young but becoming pale yellow to buff with age, and sometimes forked near the stipe. The stipe is 3–8 cm long and 2.5–4 cm thick. It is initially white but develops yellowish-brownish discolorations with age. The mushroom sometimes develops a pale green band at the top of the stipe. The spore print is white to light cream.Spores of ''R. brevipes'' are egg-shaped to more or less spherical, and measure 7.5–10 by 6.5–8.5 µm; they have a partially reticulate surface dotted with warts measuring up to 1 µm high. The cap cuticle is arranged in the form of a cutis comprising interwoven hyphae with rounded tips. There are no cystidia on the cap .
The variant ''R. brevipes'' var. ''acrior'' Shaffer has a subtle green shading at the stipe apex and on the gills. ''R. brevipes'' var. ''megaspora'' has spores measuring 9–14 by 8–12 µm.
Naming
The subalpine waxy cap is somewhat similar in appearance to ''R. brevipes'' but lacks its brittle flesh, and it has a sticky, glutinous cap. The Pacific Northwest species ''Russula cascadensis'' also resembles ''R. brevipes'', but has an acrid taste and smaller fruit bodies. Another lookalike, ''R. vesicatoria'', has gills that often fork near the stipe attachment. ''R. angustispora'' is quite similar to ''R. brevipes'', but has narrower spores measuring 6.5–8.5 by 4.5–5 µm, and it does not have the pale greenish band that sometimes develops in the latter species. The European look-alike ''R. delica'' is widely distributed, although rarer in the northern regions of the continent. Similar to ''R. brevipes'' in overall morphology, it has somewhat larger spores with a surface ornamentation featuring prominent warts interconnected by a zebra-like patterns of ridges. The milk-cap mushroom ''Lactifluus piperatus'' can be distinguished from ''R. brevipes'' by the production of latex when the mushroom tissue is cut or injured.
Distribution
It is a common ectomycorrhizal fungus associated with several hosts across temperate forest ecosystems. Typical hosts include trees in the genera ''Abies'', ''Picea'', ''Pseudotsuga'', and ''Tsuga''. The fungus has been reported in Pakistan's Himalayan moist temperate forests associated with ''Pinus wallichiana''. Fruit bodies grow singly or in groups; fruiting season occurs from summer to autumn. In western North America, where the mushroom is quite common, it is encountered most frequently in late autumn. The mushrooms are usually found as "shrumps"—low, partially emerged mounds on the forest floor, and have often been partially consumed by mammals such as rodents or deer.Studies have demonstrated that geographically separated ''R. brevipes'' populations develop significant genetic differentiation, suggesting that gene flow between these populations is small. In contrast, there was little genetic differentiation observed between populations sampled from a smaller area . ''R. brevipes'' is one of several ''Russula'' species that associates with the myco-heterotrophic orchid ''Limodorum abortivum''.
Habitat
It is a common ectomycorrhizal fungus associated with several hosts across temperate forest ecosystems. Typical hosts include trees in the genera ''Abies'', ''Picea'', ''Pseudotsuga'', and ''Tsuga''. The fungus has been reported in Pakistan's Himalayan moist temperate forests associated with ''Pinus wallichiana''. Fruit bodies grow singly or in groups; fruiting season occurs from summer to autumn. In western North America, where the mushroom is quite common, it is encountered most frequently in late autumn. The mushrooms are usually found as "shrumps"—low, partially emerged mounds on the forest floor, and have often been partially consumed by mammals such as rodents or deer.Studies have demonstrated that geographically separated ''R. brevipes'' populations develop significant genetic differentiation, suggesting that gene flow between these populations is small. In contrast, there was little genetic differentiation observed between populations sampled from a smaller area . ''R. brevipes'' is one of several ''Russula'' species that associates with the myco-heterotrophic orchid ''Limodorum abortivum''.
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