Taxon classification Fungi Russulales Russulaceae

3. Lactarius glyciosmus (Fr.) Fr. Figure 5

Lactarius glyciosmus The following morphological description includes data from Colorado specimens listed in Barge et al. (2016).

Description.

Pileus 15-50 mm in diameter, broadly convex, later becoming plane with or without a depressed center and small papilla, smooth, dry, azonate to lightly zoned especially near the margin, pale gray-brown to violet-brown with a whitish glaucous coating when immature, fading in age; margin incurved when young and remaining so or becoming straight in age. Lamellae adnate to subdecurrent, subdistant to crowded, cream to pale pinkish to pale yellow-orange. Stipe 10-40 × 3-12 mm, equal to slightly clavate, central to eccentric, smooth, dry, buff or pale salmon with a faint glaucous coating at first as in pileus, stuffed, becoming hollow, often white-mycelioid toward the base. Context pale cream. Latex scarce to undetectable, watery, white, unchanging. Odor of coconut. Taste mild to slightly acrid.

Basidiospores 7-9 × 5-7 µm, Q = 1.2-1.4, broadly ellipsoid to ellipsoid, ornamentation forming an incomplete to nearly complete reticulum. Pleuromacrocystidia 45.5-63.5 × 6.5-7.5 µm, scarce to scattered, subclavate to lanceolate; apex rounded to mucronate. Cheilomacrocystidia 33-66 × 5-9 µm, scattered to abundant, cylindrical to subclavate; apex rounded.

Ecology and distribution.

Widespread in the Northern Hemisphere in temperate, boreal, and arctic-alpine areas with Betula . In the GYE and elsewhere in the Rocky Mountains, it occurs in subalpine and alpine areas with Betula glandulosa and possibly other Betula spp., late summer.

Specimens examined.

U.S.A. MONTANA: Carbon County, Beartooth Plateau, Birch Site, near Betula glandulosa, 29 July 1997, CLC1134 = ZT6096 (MONT); 8 Aug 1998, CLC1217 (MONT); 10 Aug 1999, TWO269 (MONT); 19 Aug 1999, CLC1380 (MONT); 13 Aug 2007, ZT12723 (MONT); Carbon County, Hellroaring Plateau, Hellroaring Creek, near Betula glandulosa, 9 Aug 2015, EB111-15 (MONT). WYOMING: Park County, Beartooth Plateau, Island Lake, near Betula glandulosa, 6 Sept 2015, EB160-15 (MONT).

Discussion.

Lactarius glyciosmus is very closely related to Lactarius mammosus Fr. (Figure 2A), however, the latter has a browner pileus, stouter stature, and ecology with Pinaceae (although it has been reported with Betula) (Heilmann-Clausen et al. 1998). Lactarius vietus (Fr.) Fr. has a distinct pale zone near the stipe apex, latex that dries greenish gray, longer pleuromacrocystidia (50-90 × 7-12 µm), a mild to slightly fruity odor, and a strongly acrid taste (Heilmann-Clausen et al. 1998). The presence of Lactarius mammosus and Lactarius vietus in the Rocky Mountains is unclear. Lactarius trivialis (Fr.) Fr., which has been reported from the GYE (McKnight 1982), but could not be confirmed, is typically larger with slightly larger basidiospores (7.3-10 × 5.9-7.8 µm), more numerous pleuromacrocystidia, and a mild to acidic-fruity odor (Heilmann-Clausen et al. 1998). Lactarius nanus has larger basidiospores (7 –10.5(– 12) × 5-8 µm), larger and differently shaped pleuromacrocystidia (53 –96.5(– 114) × 6.5-11.5 µm), a mild odor, and associates with Salix .