Lactarius glyciosmus (Fr.) Fr.

Barge, Edward G. & Cripps, Cathy L., 2016, New reports, phylogenetic analysis, and a key to Lactarius Pers. in the Greater Yellowstone Ecosystem informed by molecular data, MycoKeys 15, pp. 1-58 : 13

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 .