Lactarius alpinus v. mitis 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 : 9-10

Taxon classification Fungi Russulales Russulaceae

1. Lactarius alpinus v. mitis Hesler & A.H. Sm. Figure 3

Description.

Pileus 8-20 mm in diameter (to 80 mm in Hesler and Smith 1979), plano-convex to infundibuliform, ± papillate, dry, finely rimulose to minutely squamulose, red-brown to orange-brown to pinkish cinnamon; margin finely crenulate, incurved when young, becoming straight to wavy in age. Lamellae adnate to subdecurrent, subdistant to crowded, cream to creamy tan, discoloring slightly darker where damaged. Stipe 8-23 × 5-8 mm (30-50 × 10-15 mm in Hesler and Smith 1979), equal to slightly clavate, smooth, dry, pale creamy yellow to creamy tan, solid, becoming hollow. Context concolorous with pileus. Latex scarce, watery, white, unchanging. Odor mild. Taste mild.

Basidiospores 7-9.5 × 5-7.5 µm, Q = 1.3-1.5, ellipsoid; ornamentation forming a broken to partial reticulum. Pleuromacrocystidia 60-100 × 6-10 µm, numerous, strongly projecting, mucronate to fusoid; apex acute to moniliform. Cheilomacrocystidia 50-80 × 6-10 µm, numerous, strongly projecting, mucronate to fusoid; apex acute to moniliform.

Ecology and distribution.

In western and into eastern North America with Alnus . In the GYE only one collection has been made thus far and it was from a riparian area near Alnus incana and Populus trichocarpa , late summer. Further sampling under Alnus in the Rocky Mountains is necessary.

Specimens examined.

U.S.A. MONTANA: Carbon County, Red Lodge, along Rock Creek, under Alnus incana and Populus trichocarpa , 6 Sept 2015, EB161-15 (MONT).

Discussion.

This is the first report of Lactarius alpinus v. mitis from the GYE. According to Hesler and Smith (1979), Lactarius alpinus v. mitis has duller pileus and lamellae colors than Lactarius alpinus v. alpinus Peck, which typically develops bright yellow to apricot colors; variety mitis also has longer and more conspicuous macrocystidia and a mild rather than slowly acrid taste. The collection described here likely did not reach full maturity, and the basidiomes are smaller than reported in Hesler and Smith (1979). Phylogenetic analyses including material of Lactarius alpinus v. alpinus from near the type locality suggest that Lactarius alpinus v. mitis and Lactarius alpinus v. alpinus are distinct species (Figure 2A, 2C), however a more in depth analysis incorporating type material of at least Lactarius alpinus v. mitis should be carried out before making this determination final. For an interesting discussion on Lactarius alpinus see Nuytinck and Voitk (2016) and Rochet et al. (2011).

While Lactarius alpinus v. mitis appears to be quite distantly related to Lactarius alpinus v. alpinus , it is very closely related to the European Lactarius lilacinus (Lasch) Fr., the recently described Mexican Lactarius cuspidoaurantiacus Montoya, Bandala & Garay-Serr., and to a lesser extent Lactarius lepidotus Hesler & A.H. Sm., all of which are also associated with Alnus (Figure 2A). Lactarius lilacinus is typically more pink to violet in color and has a fruity smell. Lactarius cuspidoaurantiacus appears to have more yellow-orange basidiomes, more orange colored, distant lamellae, and a Pelargonium -like odor ( Montoya et al. 2014). Lactarius lepidotus has a more gray-brown to beige pileus. Neither Lactarius lilacinus , Lactarius cuspidoaurantiacus or Lactarius lepidotus have been reported from the Rocky Mountains.