Yellow-staining milkcap

Appearance

The cap of "L. vinaceorufescens" is initially convex, then becomes broadly convex to nearly flat, and reaches diameters of 4–12 cm wide. The cap margin is rolled inwards at first, but later expands, becoming somewhat uplifted and uneven with age. The cap surface is smooth, pale pinkish cinnamon with pinkish buff at the margin when young, becoming darker pinkish cinnamon to orangey cinnamon when older, faintly zoned with bands or water spots of nearly the same color. The gills are attached to slightly decurrent, narrow, close together, and often forked near the stem. There are several tiers of lamellulae. The gills are initially whitish to pinkish buff, later spotting wine red to pinkish brown or dark reddish brown. The latex that is exuded when the mushroom is cut or injured is initially white, but rapidly turns sulfur-yellow.

The stem is 4–7 cm long by 1–2.5 cm thick, nearly equal in width throughout or enlarged slightly downward, and hollow. The stem surface is nearly smooth, with white to brownish stiff hairs at the base, pinkish-white overall, and darkening with age. The flesh is moderately thick, white to pinkish, staining bright sulfur yellow. It has an acrid taste. The spore print is white to yellowish. The mushrooms are poisonous; as a general rule, several guide books recommend to avoid the consumption of "Lactarius" species with latex that turns yellow.

The spores are roughly spherical to broadly ellipsoid, hyaline, amyloid, and measure 6.5–9 by 6–7 µm. They are ornamented with warts and ridges that sometimes form a partial reticulum, with prominences up to 0.8 µm. The basidia are four-spored, and measure 28–33 by 8–10 µm. The pleurocystidia are roughly cylindrical to narrowly club-shaped when they are young, but soon broaden in the mid portion and taper to an abrupt point; they reach dimensions of 40–68 by 9–13 µm. The cheilocystidia are roughly club-shaped or ventricose with acute apices, and measure 32–44 by 6–10 µm. Clamp connections are absent in the hyphae. The cap cuticle is a thin ixocutis composed of gelatinous hyphae that are typically 2–4 µm wide. Projecting out from the cuticle surface are the ends of numerous connective hyphae, about 5–15 µm long.

Naming

"Lactarius xanthogalactus" has nearly identical microscopic features to "L. vinaceorufescens", but macroscopically, it does not have the reddish-vinaceous stains that develop on the cap, gills, and stem of "L. vinaceorufescens", and it grows on the ground under oak. Another lookalike is "L. colorascens", but it may be distinguished from "L. vinaceorufescens" by several features: a smaller fruit body; a whitish cap that becomes brownish red with age and does not spot vinaceous or brown; bitter to faintly acrid latex; and slightly smaller spores. "L. chrysorrheus" is also similar, but it has a whitish to pale yellowish-cinnamon cap with slightly darker spots and grows under hardwoods on well-drained, often sandy soil, and its gills do not discolor or spot vinaceous or brown.

Other superficially similar species include "L. rubrilacteus", "L. rufus", "L. subviscidus", "L. fragilis" and "L. rufulus", but none of these species have the yellow staining reaction characteristic of "L. vinaceorufescens". The edible species "Lactarius helvus" has an orange-brown to light grayish-brown cap with thin bands of dark grayish-brown, a watery latex, and whitish to tan flesh with an odor resembling maple sugar or burnt sugar. "Lactarius theiogalus", the "sulfur-milk Lactarius", has an oranger cap and white latex that slowly changes yellow upon exposure to air; it is typically found in broadleaf and mixed woods.

Distribution

The fruit bodies of "Lactarius vinaceorufescens" grow scattered or in groups on the ground under pine between August and October. The species is known to develop mycorrhizal associations with Douglas fir. It is a fairly common and widely distributed species in North America. The mushroom has been found in boreal forests and high-elevation forests of the Southern Appalachians, associated with the tree genera "Picea", "Abies", and "Pinus". In California, it has been noted to commonly co-occur with "L. fragilis", "L. rubrilacteus", "Russula emetica", and "R. cremoricolor".

Habitat

The fruit bodies of "Lactarius vinaceorufescens" grow scattered or in groups on the ground under pine between August and October. The species is known to develop mycorrhizal associations with Douglas fir. It is a fairly common and widely distributed species in North America. The mushroom has been found in boreal forests and high-elevation forests of the Southern Appalachians, associated with the tree genera "Picea", "Abies", and "Pinus". In California, it has been noted to commonly co-occur with "L. fragilis", "L. rubrilacteus", "Russula emetica", and "R. cremoricolor".