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Lactarius imperceptus

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

by Michael Kuo

Found under oaks in eastern North America, Lactarius imperceptus is a brownish species with white milk that turns yellow when exposed to air . . . in theory. In practice the cap is sometimes rather pinkish, and the yellowing of the milk may be faint (even absent) and/or slow to develop. The cap is never zoned, helping to separate it from other oak-loving species with yellowing milk, like Lactarius chrysorrheus.


Ecology: Mycorrhizal with oaks (especially southern live oaks) and possibly with other hardwoods; summer and fall; widely distributed east of the Great Plains.

Cap: 2.5-9 cm; convex, with an incurved margin when young, becoming flat or shallowly depressed, often with a central bump; dry or moist; bald; dull brown to tan, cinnamon tan, pinkish brown, or paler; consistently without zones of color or texture.

Gills: Attached to the stem or beginning to run down it; close; whitish to pinkish or very pale tan; often developing cinnamon to reddish brown stains and discolorations.

Stem: 2.5-9 cm long; up to about 1.5 cm thick; more or less equal; dry or moist; without potholes; smooth; pale at first, becoming colored like the cap.

Flesh: Thin; pale, becoming pinkish; not changing when sliced, or turning slowly yellowish to yellow.

Milk: Creamy; turning slightly to substantially yellowish (often very slowly) or not yellowing appreciably; not staining tissues, or staining them yellowish; staining white paper yellow.

Odor and Taste: Odor not distinctive; taste usually acrid but sometimes weakly so.

Spore Print: White to yellowish.

Microscopic Features: Spores 7-9.5 x 6-8 µ; broadly ellipsoid; ornamentation 0.5-1.5 µ high, as amyloid warts and ridges that form broken reticula or remain scattered. Pleuromacrocystidia to about 70 x 10 µ; fusiform to fusoid-mucronate or subcylindric, often with an apical constriction. Cheilomacrocystidia similar but shorter. Pileipellis an ixolattice or ixotrichoderm, with the gelatinous material quickly dissolving in KOH mounts.

REFERENCES: Beardslee & Burlingham, 1940. (Hesler & Smith, 1979; Phillips, 1991/2005; Binion et al., 2008.) Herb. Kuo 10110904.

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Lactarius imperceptus

Lactarius imperceptus

Lactarius imperceptus

Lactarius imperceptus

Lactarius imperceptus

Lactarius imperceptus

Lactarius imperceptus

Lactarius imperceptus

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Kuo, M. (2011, March). Lactarius imperceptus. Retrieved from the MushroomExpert.Com Web site: