Lactarius torminosus, commonly known as the woolly milkcap or the bearded milkcap, is a large species of agaric fungus. It was first described scientifically by Jacob Christian Schäffer in 1774 as an Agaricus, and later transferred to the genus Lactarius in 1821 by Samuel Frederick Gray. L. torminosus officially became the type species of Lactarius in 2011 after molecular studies prompted the taxonomic reshuffling of species between several Russulaceae genera.

The caps are convex with a central depression, and attain a diameter of up to 10 cm (4 in). A blend of pink and ochre hues, the cap sometimes has concentric zones of alternating lighter and darker shades. The edge of the cap is rolled inward, and shaggy when young. On the underside of the cap are narrow flesh-colored gills that are crowded closely together. The cylindrical stem is a pale flesh color with a delicately downy surface and brittle flesh; it is up to 8 cm (3 in) long and 0.6–2 cm (1⁄4–3⁄4 in) thick. When cut or injured, the fruit bodies ooze a bitter white latex that does not change color upon exposure to air. The variety nordmanensis, in contrast, has latex that changes from white to yellow. Similar species like L. pubescens or L. villosus differ in morphology and coloration, as well as microscopic characteristics like spore shape and size.

A common and widely distributed species, L. torminosus mushrooms form on the ground singly or in groups in mixed forests of both the Old World and North America. A mycorrhizal species, it associates with various trees, most commonly birch. The species is highly irritating to the digestive system when eaten raw. The toxins, also responsible for the strongly bitter or acrid taste, are destroyed by cooking. It is valued for its peppery flavor and eaten in Russia and Finland. Studies have identified several chemicals present in the mushrooms, including ergosterol and derivatives thereof, and the pungent-tasting velleral.

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