Lactarius caespitosus Hesler & A.H. Sm.

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 : 22-23

Taxon classification Fungi Russulales Russulaceae

9. Lactarius caespitosus Hesler & A.H. Sm. Figure 11

Description.

Pileus 35-100 µm in diameter, convex to broadly convex to nearly plane, ± centrally depressed, viscid to dry, smooth, more or less azonate, cream to pale gray–brown to pale vinaceous–brown, ± discoloring ochraceous in places; margin incurved when young, becoming straight in age. Lamellae adnate to subdecurrent, crowded to subdistant, white at first, becoming pale creamy buff, ± discoloring ochraceous to brown where damaged. Stipe 30-80 × 10-35 mm, equal to clavate, viscid to dry, smooth, white, developing ochraceous to faintly violet areas where damaged, solid, becoming hollow. Context white. Latex scarce to undetectable, white, unchanging. Odor mild. Taste acrid.

Basidiospores 8-12 × 7-9 µm, Q = 1.2-1.4, broadly ellipsoid to ellipsoid; ornamentation forming a broken to partial reticulum. Pleuromacrocystidia 50-110 × 8-12 µm, scattered to numerous, subcylindric to fusoid; apex rounded to acute. Cheilomacrocystidia 40-60 × 8-12 µm, scattered to abundant, clavate to mucronate; apex rounded to acute.

Ecology and distribution.

In mountainous areas in western North America with conifers. Hesler and Smith (1979) report it as the common montane Lactarius of wet places in the spruce-fir zone of the Rocky Mountains during the summer and early fall. In the GYE, it occurs in wet depressions and near seeps as well as in drier upland sites in the montane spruce-fir zone, possibly always in the presence of Abies lasiocarpa , summer to fall.

Specimens examined.

U.S.A. MONTANA: Gallatin County, Gallatin Range, East Fork Hyalite Creek, under Abies lasiocarpa and Picea engelmannii , 25 Aug 2015, EB158-15 ( MONT); Gallatin County, Gallatin Range, Windy Pass Trail, under Abies lasiocarpa and Pinus contorta , 10 Aug 2013, EB102-13 ( MONT); Madison County, Madison Range, Big Sky, under Abies lasiocarpa , Picea engelmannii and Pinus albicaulis , 4 Sept 2004, CLC2052 ( MONT); Madison County, Madison Range, Mirror Lake, under Abies lasiocarpa , 3 Sept 2013, EB121-13 ( MONT); Madison County, Tobacco Root Mountains, Branham Lakes, under Abies lasiocarpa , 1 Sept 2014, EB0074-14 ( MONT); Sweet Grass County, Crazy Mountains, Big Timber Creek, under Abies lasiocarpa and Picea engelmannii , 1 Aug 2015, EB095-15 ( MONT). WYOMING: Park County, Beartooth Plateau, Beartooth Lake Campground, under Abies lasiocarpa and Picea engelmannii , 5 Sept 2015, EB159-15 ( MONT).

Discussion.

The European Abies associate Lactarius albocarneus Britzelm. appears to be closely related (Figure 2B), however, it has a lighter cream to dingy whitish pileus, and slowly yellowing latex and flesh ( Heilmann-Clausen et al. 1998). The western North American Lactarius kauffmanii Hesler & A.H. Sm. and Lactarius pseudomucidus Hesler & A.H. Sm. also appear to be related (Figure 2B). Lactarius kauffmanii has a dark to blackish brown pileus (although it can be lighter), smaller basidiospores (7-10 × 6.5-8 µm), and a vinaceous to tan stipe. Lactarius pseudomucidus typically has a darker and more slimy pileus, a gray to gray–brown stipe, and smaller basidiospores (7-9 × 6-7 µm). Both Lactarius kauffmanii and Lactarius pseudomucidus may be confined to Douglas fir/western hemlock forests of the Pacific Northwest ( Hesler and Smith 1979). The western North American Lactarius circellatus v. borealis Hesler & A.H. Sm. is also similar, however, its pileus is pruinose at first and generally darker and faintly zonate to zonate, it has a dry stipe (never viscid as in Lactarius caespitosus ), and its lamellae are unstaining when cut ( Hesler and Smith 1979, Methven 1997). Lactarius trivialis is also similar, however it appears to be fairly distantly related (Figure 2A); it has purplish gray to vinaceous colors of the pileus at least when young and smaller basidiospores (7.3-10 × 5.9-7.8 µm) ( Heilmann-Clausen et al. 1998). Lactarius argillaceifolius Hesler & A.H. Sm. and its varieties are also similar, however, all feature a more purplish gray pileus at least when young (similar to Lactarius trivialis ) and smaller basidiospores. Variety argillaceifolius appears to be confined to oak forests in central and eastern North America, v. megacarpus Hesler & A.H. Sm. to oak forests in coastal western North America, and v. dissimilis Hesler & A.H. Sm. is represented by only one collection from South Carolina ( Hesler and Smith 1979).