Lactarius zonarius v. riparius 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 : 29-31

Taxon classification Fungi Russulales Russulaceae

14. Lactarius zonarius v. riparius Hesler & A.H. Sm. Figure 16

Description.

Pileus 50-80 mm in diameter, depressed–convex to broadly infundibuliform, viscid to dry, smooth to ± matted–tomentose toward the margin, zonate to faintly zonate, yellow–brown to orange–brown, ± lighter toward the margin; margin incurved and matted–tomentose to cottony–tomentose when young, becoming straight and glabrous in age. Lamellae subdecurrent to decurrent, crowded, cream, staining brownish where damaged. Stipe 20-40 × 15-25 mm, equal to tapering toward the base, smooth, dry, cream, ± with small pale brown scrobicules. Context very firm, cream. Latex white, unchanging, staining lamellae brownish. Odor sweet, fruity. Taste slowly acrid.

Basidiospores 7-9 × 5.5-7.5 µm, Q = 1.2-1.4, broadly ellipsoid to ellipsoid; ornamentation forming a highly broken reticulum. Pleuromacrocystidia 40-66 × 4.5-7.4 µm, scarce to scattered, narrowly subfusiform to fusiform; apex acute to moniliform. Cheilomacrocystidia 25-49 × 4.5-5.5 µm, numerous, narrowly subfusiform to fusiform; apex acute to moniliform.

Ecology and distribution.

Originally described and reported from rich wet humus along small streams in hardwood forests in Michigan. There are very few subsequent reports. In the GYE, it occurs in rich, moist riparian areas with Populus trichocarpa , summer to fall.

Specimens examined.

U.S.A. MONTANA: Gallatin County, Bozeman, along Sourdough Creek, under Populus trichocarpa , 2013, CLC2933 ( MONT).

Discussion.

Molecularly, this taxon is very close to the European Lactarius evosmus Kühner & Romagn. (Figure 2B), which also associates with Populus , as well as Quercus , and occasionally Salix ( Heilmann-Clausen et al. 1998). It is also close to but distinct from the European Lactarius zonarius (Figure 2B). Neither Lactarius evosmus or Lactarius zonarius feature a bearded pileus margin at any point in sporocarp development. Lactarius zonarius v. riparius will likely need to be given species level status and a new name, although this hinges on examination of type material.

Similar taxa in western North America include Lactarius sanmiguelensis Hesler & A.H. Sm., described from under cottonwood in southwestern Colorado that has a pileus with cinnamon–buff zones on a pinkish buff ground color, the role of felt along the margin is pinkish buff, it does not have a distinctive odor, it is instantly and very strongly acrid, the lamellae are strongly anastomosed, pinkish buff, and do not discolor where injured, and the stipe is longer and pale pinkish buff ( Hesler and Smith 1979). Bessette et al. (2009) synonymize Lactarius sanmiguelensis and Lactarius subvillosus Hesler & A.H. Sm., the latter being undoubtedly different from the species described here. Lactarius pseudodelicatus is somewhat similar but it has a longer stipe, smaller basidiospores (6-8 × 5-6.5 µm), and much larger pleuromacrocystidia (60-100 × 7-12 µm). Lactarius psammicola A.H. Sm. and Lactarius yazooensis Hesler & A.H. Sm. are similar species with a more Eastern North American distribution in Quercus forests ( Hesler and Smith 1979).