What You Should Know
Russula dissimulans is similar to Russula densifolia in that both are initially white, bruise red, then gray, and finally black. However, Russula dissimulans is a much larger mushroom with somewhat distant, broader, thick gills and a thinner cuticle, which is difficult to peel. It is mycorrhizal with hardwoods and conifers and can be found growing alone, in groups, or scattered in summer and autumn.
It is a North American species most closely related to Russula nigricans in a group of 'blackening' Russula species. This group is part of the Nigricans clade, which forms an isolated clade along with the Archaea and Farinipes clades (Looney et al. 2016).
Other names: Red and Black Russula.
Russula dissimulans Mushroom Identification
Mycorrhizal with hardwoods or conifers; growing alone, scattered, or gregariously; summer and fall (and overwinter in warm climates); widely distributed in North America.
5-20 cm; broadly convex when young, later flat with a central depression, or shallowly vase-shaped; dry; more or less smooth, but with a waxy feel; initially whitish but soon discoloring to brownish, ashy gray, or brown (eventually almost black); the margin not lined; the skin not peeling easily.
Attached or running very slightly down the stem; thick; distant or nearly so; white to cream; bruising and discoloring slowly reddish, then grayish to blackish.
3-8 cm long; 1-4 cm thick; whitish at first, but soon darkening like the cap; bruising reddish, then blackish throughout as much as half an hour; fairly smooth.
White; hard; bruising promptly or slowly reddish on exposure, then blackish over as much as half an hour or more.
Odor and Taste
Odor is slightly fragrant, somewhat unpleasant, or not distinctive; taste mild, slightly acrid, or acrid.
KOH on cap surface negative. Iron salts on stem surface negative to weakly grayish.
Spores 6-11 x 6-9 µ; widely elliptical to subglobose; with ornamentation under 1 µ high, connectors forming partially to completely reticulate areas. Pileipellis 20-150 µ thick; cutis-like, with horizontal elements, tightly interwoven; in KOH "with globules of brown pigment giving them the appearance of transparent intestines" (Roberts, 2008); not embedded in a gelatinous matrix; pileocystidia absent.
Photo 1 - Author: alan_rockefeller (Attribution-ShareAlike 4.0 International)
Photo 2 - Author: alan_rockefeller (Attribution-ShareAlike 4.0 International)
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