Lactarius alnicola, commonly known as the golden milkcap, is a species of fungus in the family Russulaceae. The fruit bodies produced by the fungus are characterized by a sticky, vanilla-colored cap up to wide with a mixture of yellow tones arranged in faint concentric bands. The stem is up to long and has yellow-brown spots. When it is cut or injured, the mushroom oozes a white latex, which has an intensely peppery taste. The acrid taste of the fruit bodies renders them unpalatable. The fungus is found in the western United States and Mexico, where it grows in mycorrhizal associations with various coniferous trees species, such as spruce, pine and fir, and deciduous species such as oak and alder. It has also been collected in India. Two varieties have been named: var. pitkinensis, known from Colorado, and var. pungens, from Michigan.
Taxonomy
The species was originally described by American mycologist Alexander H. Smith in 1960, from a collection made near Warm Lake, Idaho, two years prior. The species was originally collected under alders with conifers nearby, and its specific epithet reflects the presumed association between the species—alnicola means "living with alder". Researchers subsequently discovered that the species has a relationship with conifers, not with alders, as the name implies. The mushroom is commonly known as the "golden milkcap".
Lactarius alnicola is classified in subsection Scrobiculati of section Piperites in the genus Lactarius. Species in this subsection are characterized by having a milk-white to creamy or whey-like latex that soon turns yellow upon exposure to air, and which may stain freshly cut surfaces of the fruit body yellow. Further, the cap margin is bearded, strigose (covered with sharp, straight, and stiff hairs), and coarsely tomentose or woolly when young. Other species in the subsection include L. subpaludosus, L. delicatus, L. torminosus, L. payettensis, L. gossypinus, L. pubescens, L. resimus and L. scrobiculatus (the type species of the subsection).
Description
The cap is wide, initially convex but becoming depressed to funnel-shaped in maturity. The cap margin is initially rolled inward, then becomes uplifted as the cap expands. The cap surface is sticky to slimy, and near the margin there are matted "hairs" beneath the slimy or sticky layer. The color of the cap surface is yellow-ochre, sometimes with concentric bands of lighter and darker shades; the color becomes paler near the margin. The gills are adnate (squarely attached to the stem) to decurrent (attached to and running down the length of the stem), narrow, and crowded closely together. Forked near the stem, the gills are initially whitish before becoming pale ochraceous-buff. There are many lamellulae—small gills that do not extend completely to the stem.
The stem is long and thick, nearly equal in width throughout or tapered downward, dry, hard, coarsely pitted, and whitish to cream yellowish. It is initially solid, then becomes hollow with age. The flesh is thick, hard, whitish, and slowly stains pale yellow after the mushroom has been cut open. It has no distinctive odor, while the taste is immediately acrid. The latex is sparse, white on exposure to air, and unchanging or very slowly changing color to yellow. It stains cut flesh yellow, and tastes acrid. According to mycologist David Arora, the oak-loving central and southern Californian population of this species has a more latent acrid taste. The spore print may range slightly in color: thin deposits are white, thick deposits are more yellow. The mushroom is considered inedible because of the intensely peppery taste.
Microscopic characters
The spores are 7.5–10 by 6–8.5 µm, ellipsoid, and ornamented with warts and narrow bands that form a partial reticulum. The surface prominences are up to 1 µm high, but mostly in the range 0.3–0.6 µm. The spores are hyaline (translucent) and amyloid, meaning that they will adsorb iodine when stained with Melzer's reagent. The basidia, the spore-bearing cells, are four-spored, and measure 37–48 by 8–11 µm. The cap cuticle is an ixocutis (a tissue layer on the surface of a mushroom made of a layer of gelatinous hyphae) made of encrusted hyphae that are 3–5 µm wide.