Lactarius vietus (commonly known as the grey milkcap) is a species of fungus in the family Russulaceae, first described by Elias Magnus Fries.

It produces moderately sized and brittle mushrooms, which grow on the forest floor or on rotting wood.

It grows in autumn months and is fairly common in Europe, North America and eastern Asia.

[3][4] In his 1838 work Epicrisis systematis mycologici, Fries reclassified the species as a Lactarius, giving it its current name.

[10] They are thin and flaccid,[9] and there are three to four tiers of lamellulae (short gills that do not reach the stem from the cap margin).

[15][16] In shape, the spores are elliptic, with a moderately well-developed network of ridges, measuring between 8 and 9.5 by 6.5 to 7.5 micrometres (μm).

[13] Lactarius mammosus, a species described by Fries but not often mentioned by the mycological community for some time after his death, is also similar.

Meinhard Moser, examining the identity of L. mammosus, concluded that it "is certainly more closely related to L. vietus than to L. fuscus, but differs in habit and colour.

[10] Although described by many mycologists as inedible,[10][18] David Pegler claims that its acrid taste can be removed after boiling, allowing it to be consumed.

[12] Lactarius vietus is fairly common, and can be found growing in moist areas under trees in autumn,[10] often among Sphagnum moss.

[21] It can also be found growing on rotting wood or other hard surfaces; specimens have been observed on both conifer and hardwood logs.