What You Should Know
Lactarius glyciosmus is a semi-edible mushroom in the genus Lactarius. Mycorrhizal, it can be found growing in the soil at the base of birch trees in Europe. It is typically colored a grayish lilac, with the sometimes hollow stem a little lighter colored than the cap. It has crowded, decurrent gills, and smells strongly of coconuts.
This milkcap is drab and undistinguished, as are so many other mushrooms in this difficult genus, and so the habitat and its unusual odor are key field characters that should be noted if you want to fine down the identification options.
On the West Coast Lactarius glyciosmus might be confused with Lactarius cocosiolens, which also smells like coconuts but features a slimy brownish orange cap and appears in coastal, birch-less forests. Whether or not our North American version of Lactarius glyciosmus is the same as the original, European species (first described by Fries in 1818), has not been established.
Other names: Coconut Milkcap
Lactarius glyciosmus Mushroom Identification
Mycorrhizal with paper birch (possibly also with other birches); also reported with alder; growing alone, scattered, or gregariously; late summer and fall; widely distributed in North America wherever the host trees occur.
2–7 cm; thin and fragile; convex with an inrolled margin when young, becoming shallowly depressed, flat, or shallowly vase-shaped; dry; bald; finely roughened; pinkish buff; sometimes featuring vague concentric zones of color or texture.
Attached to the stem or running down it; close; short-gills frequent; whitish to yellowish; not bruising or discoloring.
3–7 cm long; up to 8–15 mm thick; more or less equal; dry; without potholes; bald; colored like the cap or paler.
Insubstantial; pale; not changing when sliced.
White; often scanty; not changing on exposure to air; not staining tissues.
Odor and Taste
Odor strongly of coconuts; taste slightly acrid.
KOH yellowish on cap surface.
Spores 5.5–9 x 5.5–7 µm; broadly ellipsoid to subglobose; ornamentation as thick, amyloid spines and ridges extending 0.5–1 µm high, forming zebroid patterns and partially reticulated areas. Pleuromacrocystidia and cheilomacrocystidia 50–90 x 5–7.5 µm; narrowly fusiform; occasionally developing an apical knob; hyaline to yellowish in KOH; smooth; thin-walled. Pileipellis a cutis; hyaline to yellowish in KOH.
Lactarius glyciosmus Taxonomy and Etymology
This mushroom was described in 1818 by the great Swedish mycologist Elias Magnus Fries, who gave it the binomial scientific name Agaricus glyciosmus. It was Fries himself who, in 1838, transferred this species to the genus Lactarius, thus establishing its currently-accepted common name Lactarius glyciosmus.
Synonyms of Lactarius glyciosmus include Lactarius impolitus, Agaricus glyciosmus Fr., Galorrheus glyciosmus (Fr.) P.Kumm., and Lactifluus glyciosmus (Fr.) Kuntze.
The generic name Lactarius is Latin and means producing milk (lactating) - a reference to the milky latex that is exuded from the gills of milkcap fungi when they are cut or torn. The specific epithet glyciosmus also comes from Ancient Greek words glukos meaning sugar (or sugary), and osmos meaning smell. Sweet-smelling is a suitable translation, as many people consider the smell of coconut to be sweet.
Photo 1 - Author: Andreas Kunze (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 2 - Author: Strobilomyces (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 3 - Author: Ian Alexander (Creative Commons Attribution-Share Alike 4.0 International)