The fruit bodies produced by the fungus are characterized by a sticky, vanilla-colored cap up to 20 cm (8 in) wide with a mixture of yellow tones arranged in faint concentric bands.

The species was originally described by American mycologist Alexander H. Smith in 1960, from a collection made near Warm Lake, Idaho, two years prior.

Further, the cap margin is bearded, strigose (covered with sharp, straight, and stiff hairs), and coarsely tomentose or woolly when young.

The flesh is thick, hard, whitish, and slowly stains pale yellow after the mushroom has been cut open.

[3] According to mycologist David Arora, the oak-loving central and southern Californian population of this species has a more latent acrid taste.

[8] The spores are 7.5–10 by 6–8.5 μm, ellipsoid, and ornamented with warts and narrow bands that form a partial reticulum.

[3] In their 1979 monograph of North American Lactarius species, Hesler and Smith named two varieties of L. alnicola.

pungens, reported only from mixed forests in Michigan, is similar but has a tacky surface that soon dries, a dull ochraceous to ochraceous-tan cap with an ochraceous-tawny center.

[7] Novice mushroom hunters may mistake L. alnicola for the edible species Cantharellus cibarius,[8] which has a vase-shaped fruit body with strongly decurrent gills.

[10] L. olympianus associates with conifers and has a pale yellow-ochre, frequently zonate cap, but may be distinguished by its stem, which is usually covered with spots.

The ectomycorrhizae that the fungus forms in association with Picea engelmannii have been shown to contain lactifers (latex-producing cells) and pigments similar to the fruit body.

[16] Fruit bodies of the fungus grow in groups on the ground under alders and conifers, usually appearing between July and October.

[20] Lactarius alnicola generally establishes symbiotic associations with alder trees (Alnus spp.)

As a mycorrhizal fungus, it improves the intake of nutrients for the tree by promoting nitrogen absorption from the soil.