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Lactarius mucidus

[ Basidiomycota > Russulales > Russulaceae > Lactarius . . . ]

by Michael Kuo

"Lactarius mucidus," in English, means "the snotty Lactarius"--a reference to the very slimy cap and stem. Other distinguishing features for this species include the dark brown colors, the pale margin of the cap, the burning-acrid taste, and the white milk (which may or may not dry yellowish to greenish). Lactarius mucidus was originally described from North Carolina (Burlingham, 1908), and its documented range has since been expanded to include much of northeastern North America. Several varieties of Lactarius mucidus were described by Hesler & Smith (1979), primarily on the basis of the color of the dried milk, but a contemporary study of this group is needed.

In western North America Lactarius mucidus is replaced by Lactarius kauffmanii and Lactarius pseudomucidus. Both are larger than their eastern counterpart. Lactarius kauffmani features a brownish orange stem and orangish gills; Lactarius pseudomucidus has a brown stem and features whitish gills that stain brown.


Ecology: Mycorrhizal with conifers; growing alone or gregariously; late summer to early winter; distributed in eastern North America north and east of a line from northern Michigan to the southern Appalachians. The illustrated and described collection is from New Jersey.

Cap: 3–6 cm; convex when young; becoming planoconvex or shallowly depressed; sticky; bald, but finely rugged; overall very dark brownish gray or grayish brown, fading to brown—with a pale buff margin.

Gills: Broadly attached to the stem; close; short-gills frequent; whitish; sometimes stained greenish to yellowish by the milk.

Stem: 2–4 cm long; about 1 cm thick; more or less equal; sticky; bald; without potholes; brownish.

Flesh: Whitish to brownish; unchanging when sliced.

Milk: White; sometimes staining surfaces slowly yellowish to greenish; staining white paper yellowish to greenish overnight.

Odor and Taste: Odor fragrant; taste quickly burning-acrid.

Spore Print: Reported as white by Hesler & Smith (1979).

Microscopic Features: Spores 7–8.5 x 6.5–7.5 µm; subglobose or broadly ellipsoid; ornamentation consisting of amyloid warts and ridges extending 0.5–1 µm high, forming a wide-meshed reticulum; ridges often quite thick (0.5 µ). Hymenial macrocystidia 60–75 x 10–12.5 µm; fusiform; occasionally with a tiny apical mucro; thin-walled; smooth; hyaline to yellowish in KOH. Pileipellis a thick ixotrichoderm; hyaline in KOH.

REFERENCES: Burlingham, 1908. (Hesler & Smith, 1979; Smith, Smith & Weber, 1979; Phillips, 1991/2005; Lincoff, 1992; Miller & Miller, 2006.) Herb. Kuo 10101505.

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Lactarius mucidus

Lactarius mucidus

Lactarius mucidus

Lactarius mucidus

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Kuo, M. (2017, June). Lactarius mucidus. Retrieved from the MushroomExpert.Com Web site: