Lactarius pallidomarginatus Barge & C.L. Cripps

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 : 16-19

Taxon classification Fungi Russulales Russulaceae

6. Lactarius pallidomarginatus Barge & C.L. Cripps Figure 8

Lactarius pallidomarginatus The following morphological description is from Colorado material which includes the holotype and all are listed in Barge et al. (2016)

Description.

Pileus 20-50 mm in diameter, convex to broadly convex to plane with or without a depressed center, smooth, subviscid to dry, azonate, blotchy light tan to light brown, developing violet stains, lighter (to cream) toward margin; margin in curved when young, remaining so or becoming nearly straight in age. Lamellae adnate to subdecurrent, subdistant to slightly crowded, white to pale yellow-cream, staining violet where damaged. Stipe 10-40 × 5-10 mm, equal to slightly clavate, smooth, dry, white to cream, staining violet where damaged, hollow. Context white to cream, staining violet where damaged. Latex scarce to undetectable, watery, white, staining tissue violet. Odor mild. Taste mild.

Basidiospores 8-10 × 6.5-8 µm, Q = 1.1-1.4, broadly ellipsoid to ellipsoid; ornamentation forming an incomplete to dense reticulum. Pleuromacrocystidia 81.5-112 × 9-10 µm, scarce to scattered, cylindrical to lanceolate; apex acute to moniliform. Cheilomacrocystidia 48-101.5 × 7.5-13 µm, scattered, cylindrical to lanceolate; apex acute to moniliform.

Ecology and distribution.

Known from only a few alpine localities in the central and southern Rocky Mountains with Salix planifolia and possibly also Salix glauca , late summer.

Specimens examined.

U.S.A. WYOMING: Sublette County, Wind River Range, Union Peak, near Salix glauca , 22 Aug 1994, ZT5229 (MONT).

Discussion.

This species was recently described ( Barge et al. 2016) from the alpine zone in Southern Colorado with Salix . It is tentatively included here because a collection morphologically matching the type was made by Dr Egon Horak from the Wind River Range of Wyoming (technically in the southern GYE) with Salix glauca . Interestingly, out of all of the species examined thus far, Lactarius pallidomarginatus appears most closely related to the bright yellow, violet-staining Salix associate Lactarius aspideus (Figure 2A), to which it bares little resemblance.

In the Rocky Mountains, Lactarius pallidomarginatus is most easily confused with Lactarius nanus , Lactarius glyciosmus , Lactarius montanus , and Lactarius aff. brunneoviolaceus . The basidiomes of Lactarius nanus do not stain violet where damaged and it produces basidiospores with thicker, more jagged ridges, and macrocystidia with more rounded apices (see Barge et al. 2016). Lactarius glyciosmus also does not stain violet where damaged, it has an odor of coconut, slightly smaller basidiospores (7-9 × 5-7 µm), and smaller cheilomacrocystidia (33-66 × 5-9 µm). The closely related violet-staining Lactarius montanus produces basidiomes which are typically much more robust and stain green on the stipe and pileus surface with KOH. Lactarius montanus also has a strongly resinous odor and taste, and is mainly subalpine with conifers. See comments under Lactarius aff. brunneoviolaceus for features differentiating Lactarius pallidomarginatus from that taxon. See Barge et al. (2016) for features differentiating Lactarius pallidomarginatus from the European taxon Lactarius pseudouvidus Kühner.