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Lactarius argillaceifolius var. megacarpus

[ Agaricomycetes > Russulales > Russulaceae > Lactarius . . . ]

by Michael Kuo

This West-Coast mushroom is currently considered a variety of the eastern North American species Lactarius argillaceifolius, but its differences are substantial and it would not surprise me if DNA analysis were to reveal separate phylogenetic species--in which case the rules of taxonomy would dictate that the West-Coast mushroom become "Lactarius megacarpus."

Lactarius argillaceifolius var. megacarpus is a large, messy species of Lactarius associated with coast live oak and tanoak from southern Oregon to Baja California. Its cap, when fresh, is a dingy purplish color; its gills become dingy yellowish with age; and its off-white milk stains surfaces dingy brownish . . . in short, it's a dingy mushroom. Under the microscope it features partially reticulate, ellipsoid spores with low ornamentation.


Ecology: Mycorrhizal with coast live oak and tanoak; growing alone or gregariously; winter; coastal Oregon to Baja California.

Cap: 7-30 cm across when mature; convex, becoming flat with a central depression, or shallowly vase-shaped; drab lilac brown, fading to dirty buff; without zones; bald or minutely pocked and rugged; slimy when fresh.

Gills: Broadly attached to the stem; close or nearly distant; creamy whitish when young, but soon becoming dirty yellowish and, eventually, pale dingy cinnamon; stained slowly brownish to brown or brownish gray by the latex where damaged.

Stem: 6-20 cm long; 2-5 cm thick; more or less equal; whitish, discoloring to yellowish or brownish in age; dry or slightly sticky; bald; without potholes.

Flesh: Whitish; unchanging on exposure.

Milk: Off-white; unchanging when exposed; staining tissues brown to brownish.

Odor and Taste: Odor not distinctive; taste weakly to moderately acrid (especially the latex).

Spore Print: Whitish to very pale yellowish.

Chemical Reactions: KOH on cap surface yellow.

Microscopic Features: Spores 7-10.5 x 6.5-8 µ; broadly ellipsoid; ornamentation under 0.5 µ high, composed of warts and ridges that often form partial reticula. Pleuromacrocystidia fusiform; to about 100 µ long. Cheilomacrocystidia similar but usually shorter. Pileipellis an ixocutis or ixolattice.

REFERENCES: Hesler & Smith, 1979. (Smith, Smith & Weber, 1979; Arora, 1986; Canduso, Genari & Ayala, 1994; Methven, 1997.) Herb. Kuo 01150505.

This site contains no information about the edibility or toxicity of mushrooms.


Lactarius argillaceifolius var. megacarpus

Lactarius argillaceifolius var. megacarpus

Lactarius argillaceifolius var. megacarpus
Pleuromacrocystidium and Basidia

Lactarius argillaceifolius var. megacarpus

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Kuo, M. (2011, February). Lactarius argillaceifolius var. megacarpus. Retrieved from the MushroomExpert.Com Web site: