Lactarius luculentus v. laetus 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 : 44-45

Taxon classification Fungi Russulales Russulaceae

23. Lactarius luculentus v. laetus Hesler & A.H. Sm. Figure 25

Description.

Pileus 30-50 mm in diameter, broadly convex to broadly infundibuliform, ± umbonate, smooth, viscid when wet but soon dry, yellow–orange to dull orange to brilliant orange to orange–brown; margin straight when young to wavy in age. Lamellae adnate to decurrent, crowded to subdistant, cream to pale yellow–orange. Stipe 20-60 × 5-10 mm, equal to slightly clavate to tapering toward the base, smooth, subviscid to dry, lighter than to concolorous with the pileus, typically getting lighter toward the apex, sometimes with scattered small scrobicules present, solid, becoming hollow. Context cream to pale yellow. Latex scarce, white, unchanging. Odor mild. Taste mild to slightly bitter.

Basidiospores 7-10 × 5.5-8 µm, Q = 1.2-1.5, broadly ellipsoid to ellipsoid; ornamentation forming a very broken reticulum. Pleuromacrocystidia 60-98 × 8-12 µm, scattered to numerous, strongly projecting, subfusiform to fusiform; apex acute. Cheilomacrocystidia none observed, possibly absent.

Ecology and distribution.

In western North America with conifers. In the GYE it occurs in the montane spruce-fir zone, summer.

Specimens examined.

U.S.A. MONTANA: Sweet Grass County, Crazy Mountains, Big Timber Creek, under Abies lasiocarpa and Picea engelmannii , 1 Aug 2015, EB097-15 (MONT).

Discussion.

This is the first report of this taxon from the GYE under the name Lactarius luculentus v. laetus . Previous reports of Lactarius aurantiacus (Pers.) Gray from subalpine areas in the GYE ( McKnight 1982) may refer to Lactarius luculentus v. laetus .

Variety laetus is distinguished from var. luculentus by a brighter orange pileus as opposed to orange–brown and a mild to slightly bitter taste as opposed to slightly acrid ( Hesler and Smith 1979). At the molecular level, there is some divergence within Lactarius luculentus (Figure 2C, see also Barge et al. 2016) and there may be more than one species hiding under the name, although more specimens need to be examined and sequenced before making any nomenclatural changes.

Lactarius luculentus v. laetus is very closely related to Lactarius aurantiacus and Lactarius lanceolatus (Figure 2C) and morphological differences between them are subtle. Lactarius lanceolatus appears to have longer and more numerous cheilomacrocystidia (35.5-89 × 5-10 µm), longer pleuromacrocystidia (73.5-127 × 6.5-10 µm), as well as an alpine ecology with Salix . Lactarius aurantiacus also appears to have slightly longer pleuromacrocystidia (68.6-119.4 × 7.6-12.7 µm), and, while it occupies similar habitats to Lactarius luculentus v. laetus , it may be absent from western North America outside of Alaska ( Barge 2015).

The closely related Betula associate Lactarius lapponicus Harmaja (syn.: Lactarius duplicatus A.H. Sm.) (Figure 2C) has yellowing latex as opposed to white, unchanging latex, and appears to have a more boreal to arctic distribution ( Heilmann-Clausen et al. 1998); it has not been reported from the Rocky Mountains. The closely related Lactarius substriatus A.H. Sm. and Lactarius subflammeus Hesler & A.H. Sm. (Figure 2C) have slightly smaller basidiospores (6.5-9 × 6-8 µm, 7.5-9 × 6.5-7.5 µm respectively), a slightly acrid taste, and are scarlet when young ( Hesler and Smith 1979). The latex of Lactarius substriatus also slowly stains pale yellow. Phylogenetic analyses suggest Lactarius substriatus and Lactarius subflammeus are conspecific, and that yellowing latex is a variable feature within the combined species, although more specimens should be sequenced before making this determination final. Neither of these taxa have been reported from the GYE and their distribution seems to be centered along the Pacific Northwest coast. The morphologically similar Lactarius subviscidus , also centered along the Pacific Northwest coast, typically has smaller and more fragile basidiomes, a slightly acrid taste and unchanging latex which stains white paper yellow ( Hesler and Smith 1979). In the Rocky Mountains, Lactarius luculentus v. laetus and Lactarius badiosanguineus occur in the same habitat and can easily be confused. However, the latter has slightly smaller basidiospores (7-9.5 × 6-8 µm) and typically has a more red–brown pileus which is often darker toward the center and lighter toward the margin.