Russula densifolia
Description
Russula densifolia is a species of agaric fungus in the family Russulaceae. A widespread species, it is found in Asia, Europe, and North America, where it fruits on the ground in mixed and deciduous forests. Fruit bodies are robust and squat. The mushrooms are characterized by the red and then black color changes that occur in the flesh when it is bruised, and a relatively thick cap cuticle.
This is an edible mushroom, but in some areas of Asia, it is mild to moderately toxic and may cause gastrointestinal upset if consumed. Several bioactive compounds have been isolated and identified from the mushroom.
Common names: Crowded Russula, The Reddening Russula.
Mushroom Identification
Ecology
Mycorrhizal with hardwoods or conifers; growing alone, scattered, gregariously, or in dense troops; summer and fall (also overwinter in warmer climates); widely distributed in North America.
Cap
4-15 cm; broadly convex when young, later flat with a central depression, or shallowly vase-shaped; sticky at first or when wet; more or less smooth, or finely felty to the touch; initially white but soon discoloring to brownish, ashy gray, brown, or blackish; bruising slowly reddish, then blackish; the margin initially somewhat inrolled, not lined or lined faintly and widely; the cap skin peeling easily about halfway to the center.
Gills
Attached or running very slightly down the stem; narrow; close or crowded (sometimes nearly distant); white to cream, eventually yellowish; bruising slowly reddish, then blackish.
Stem
1.5-9 cm long; 1-3.5 cm thick; white but soon darkening like the cap; bruising reddish, then blackish throughout as much as half an hour; smooth or finely felty.
Flesh
White; hard; bruising promptly or slowly reddish on exposure, then blackish throughout as much as half an hour.
Odor and Taste
Odor not distinctive; taste mild or slowly slightly to very acrid.
Chemical Reactions
KOH on cap surface negative. Iron salts on stem surface negative.
Spore Print
White.
Microscopic Features
Spores 7-11 x 6-8.5 µ; elliptical to subglobose; with warts to .7 µ high; connectors usually forming partial or complete reticula. Pileipellis up to 500 µ thick; occasionally disposed as a single, cutis-like layer but more commonly two-layered, with the lower level densely interwoven and cutis-like and the upper level composed of fairly erect elements embedded in a gelatinous matrix; pileocystidia absent.
Look-Alikes
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Has adnate, widely spaced gills and turns reddish-brown before blackening.
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Has cap dry, rarely subviscid when wet (as opposed to viscid, shining when dry), gills usually subdistant, rarely close or distant, and cap cuticle less than 150 microns thick, (Thiers).
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Stains directly to black when bruised and tastes mild, like menthol, (Miller).
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Has sepia to grayish-brown rather than a yellow-brown cap, less tendency to redden before blackening, close but not crowded gills (as opposed to crowded), mild taste (as opposed to mild to somewhat peppery in flesh and always peppery in gills), and mild or wine-barrel odor (as opposed to faintly earthy).
Russula acrifolia
The latter's gills do not change color when bruised.
History
The species was first described by Louis Secretan in 1833 as Agaricus adustus var. densifolius. In 1876, Claude-Casimir Gillet transferred it to the genus Russula. Russula densifolia is classified in the section Nigricantes of Russula subgenus Compactae, which consists of species with robust, squat fruit bodies that discolor to brown or black.
Synonyms of Russula densifolia Secr. ex Gillet include Russula acrifolia Romagn.
Russula, the generic name, means red or reddish, and indeed many of the brittlegills have red caps. The specific epithet densifolia means 'with densely packed leaves - and in mushrooms that means closely-spaced gills.
Photo sources:
Photo 1 - Author: Jerzy Opioła (CC BY-SA 2.5)
Photo 2 - Author: Ron Pastorino (Ronpast) (CC BY-SA 3.0)
Photo 3 - Author: Thkgk (CC BY-SA 3.0)
