Purple-staining bearded milk cap

The cap of L. repraesentaneus is 6–18 cm (2.4–7.1 in) wide, convex to broadly funnel-shaped. The margin (the edge of the cap) is conspicuously bearded on young specimens. The cap surface is faintly zoned to azonate, with a thin layer of matted fibers, often becoming scurfy with age. It is dry to somewhat sticky, light yellow to orange-yellow, sometimes with rusty tints when older. The attachment of the gills to the stem is slightly decurrent—running slightly down the length of the stem. The gills are moderately broad, close to crowded, sometimes forked near the stem. Normally a cream to pale ochraceous color, they will stain dull lilac to purple when bruised. The stem is 5–12 cm (2.0–4.7 in) long, 1–3 cm (0.4–1.2 in) thick, nearly equal in width throughout or enlarged downward, hollow at maturity, sticky to dry, scrobiculate (coarsely pitted), pale yellow to orange-yellow, and stains dull lilac to purple. The flesh is firm, brittle, white, and will stain dull lilac to purple when cut. The odor is sometimes faintly fragrant or not distinctive, but when the mushroom is dry it smells intensely of soap. Its taste is mild to slightly acrid or somewhat bitter, and the flavor has been compared to sweet flag (Acorus calamus). The abundant amount of latex produced by the mushroom is white to cream, unchanging, staining all tissues dull lilac to purple. It tastes mild to slightly acrid or somewhat bitter. The spore print is yellowish. The fruit bodies are poisonous and consumption will cause stomach aches, but the nature of the toxic agents has not been identified. A new form, Lactarius repraesentaneus f. immutabilis, was described from Le Sappey, in the Haute-Savoie department of southeastern France in 2011. It differs in the staining reaction of its injured flesh. The spores are 8–12 by 6.5–9 µm, broadly ellipsoid to ellipsoid, ornamented with warts and ridges that do not form a reticulum, prominences up to 0.8 µm high, hyaline, and amyloid. The cap cuticle is an ixocutis—with the hyphae embedded in a slimy or gelatinized layer.