Lactarius nanus J. Favre

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 : 10-12

Taxon classification Fungi Russulales Russulaceae

2. Lactarius nanus J. Favre Figure 4

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

Description.

Pileus 10-50 mm in diameter, shallowly convex to plano-convex becoming plane to infundibuliform, ± papillate, smooth, slightly viscid to dry, with whitish glaucous coating when immature, easily rubbing away or fading in age, deep brown to gray-brown to liver brown with lighter and darker areas present, often lighter toward margin, becoming lighter overall upon desiccation; margin straight when young becoming upturned and wavy to convoluted in age. Lamellae adnate to subdecurrent, subdistant, cream when immature becoming dingy cream to light tan in age, sometimes with a faint pinkish tinge, discoloring to dingy tan where damaged. Stipe 5-30 × 3-15 mm, equal to clavate, central, smooth, dry, at first covered with whitish glaucous coating as in pileus, pale apricot to dingy cream-tan, hollow. Context dingy cream to brownish. Latex scarce to undetectable, watery, white, unchanging. Odor mild. Taste mild to slightly acrid.

Basidiospores 7 –10.5(– 12) × 5-8 µm, Q = 1.1-1.6, subglobose to ellipsoid; ornamentation forming an incomplete reticulum. Pleuromacrocystidia 53 –96.5(– 114) × 6.5-11.5 µm, scattered to abundant, lanceolate; apex acute to moniliform. Cheilo macrocystidia 26-91.5 × 7.5-10 µm, scattered to abundant, subulate to linear; apex acute to rounded.

Ecology and distribution.

Widespread in arctic-alpine areas in the Northern Hemisphere with Salix . In the GYE and elsewhere in the Rocky Mountains it occurs above tree line in alpine areas with Salix arctica , Salix reticulata , and Salix planifolia , late summer.

Specimens examined.

U.S.A. MONTANA: Carbon County, Beartooth Plateau, Highline Trail, among shrubby and dwarf Salix , 7 Aug 1998, CLC1221 ( MONT); among Salix reticulata and other Salix spp., 8 Aug 1998, ZT6422 ( MONT); among Salix arctica , Salix planifolia and Salix reticulata , 18 Aug 2013, EB106-13 ( MONT). WYOMING: Park County, Beartooth Plateau, Frozen Lakes, among Salix arctica , 21 Aug 1999, CLC1403 ( MONT); Park County, Beartooth Plateau, Solifluction Terraces, among Salix arctica , Salix planifolia and Salix reticulata , 11 Aug 2012, EB125 ( MONT).

Discussion.

Lactarius nanus is morphologically and phylogenetically close to Lactarius hysginoides Korhonen & T. Ulvinen (Figure 2A), however, the latter has a more cinnamon-toned pileus, smaller basidiospores (6.5-8.5 × 4.9-7.1 µm), and occurs in boreal areas with Betula , Picea and Salix ; it has not been reported from the Rocky Mountains. Lactarius pallidomarginatus Barge and C.L. Cripps is also similar, however, it is a violet staining species. Differences between Lactarius nanus and Lactarius glyciosmus (Fr.) Fr. are discussed in the comments section under the latter.