Lactarius rubrobrunneus H.T. Le & Nuytinck
MycoBank number: MB811746; Facesoffungi number: FoF00639
Basidiocarps medium sized. Pileus 15−80 mm diam., convex to widely depressed or infundibuliform, papillate; surface dry, greasy, slightly rugulose, dark brown (8F5−6) in center, reddish orange (7A6−8) to light reddish brown to yellow-brown (6C6−7) to brown (6D7) at the margin. Lamellae 1−4 mm broad, decurrent, crowded, with 3−4 series of lamellulae, forked, cream to grayish orange (5B4−5), sometimes paler, discoloring with reddish brown spots in age. Stipe 50−105 × 2−8 mm, cylindrical to tapering upwards, central, dry, smooth, whitish to pale cream pruinose at apex, light brown (6D4) to brown (6E7) to dark brown (6F6), fistulose, hairy at base. Context 1−3 mm thick in pileus, cream to brownish cream (5B4−5), odor strong, reminiscent of L. quietus or Pentatomidae bugs; taste mild. Latex watery white to white, abundant, unchanging on exposure, unchanging on white tissue paper and on a white cotton handkerchief and with 10 % KOH, taste mild. Macrochemical reaction no reaction on context with 10% KOH, or with FeSO4. Basidiospores subglobose to broadly ellipsoid, 6.1−6.6−6.9−7.4(−7.5) × 5.6−6.0−6.3−6.9(−7.0) μm, Q = 1.05−1.10−1.11−1.23 (n = 40); ornamentation amyloid, an incomplete reticulum up to 1 μm high, consisting of blunt and irregular ridges, connected by thinner ridges, isolated warts common; plage inamyloid to distally amyloid. Basidia 41−57 × 12−16 μm, 4-spored, some 2-spored, subclavate, with guttate contents. Pleuromacrocystidia rare, 38−50 × 10−14 μm, not protruding, with guttate contents. Pleuropseudocystidia abundant, slightly protruding, 3−7 μm diam., with fine granules, irregular to tortuous, sometimes with broadened apex. Lamellar edge heterogeneous, consisting of basidia and marginal cells without cheilocystidia, marginal cells abundant, 15−36 × 5−12 μm, mostly cylindrical to subcylindrical to subclavate. Lamellar trama a combination of globose cells, septate hyphae and lactiferous hyphae. Pileipellis a transition between epithelium and hyphoepithelium, with or without a thin layer of about 5−10 μm thick, repent hyphae, subpellis layer consisting of small to large, globose cells, up to 35 μm diam., layer about 70−100 μm thick.
Habitat: gregarious in montane tropical forests with Fagaceae.
Collections examined: THAILAND, Chiang Mai province, Jomthong district, Bahn Luang sub-district, Doi Inthanon National Park, junction of highway 1009 and road to Mae Cham, N19º31.58 E98º29.64, alt. 1703 m, 25/06/2004, LTH149 (GENT!, CMU!, SFSU!); Mae Hong Son province, Huai Nam Dang National Park, nature trail, alt. 1538 m, N19º18.29 E98º35.88, 29/06/2005, LTH334 (GENT!, CMU!, SFSU!); Chiang Mai province, Mae-On district, Huaikaew sub-district, Bahn Mae Kampong, N18º51.43 E99º22.09, alt. 1450 m, 15/07/2012, KW356 (AV12-044) (holotype, GENT!, isotype, MFLU!).
Notes: Lactarius rubrobrunneus is recognized by its reddish brown to orange-brown cap with a darker brown shade in the center. Lactarius rubrobrunneus differs from L. fuscomaculatus by the lack of dark brown spots on cap. Compared to L. fuscomaculatus, all collections of L. rubrobrunneus have a thinner layer of terminal hyphae in the pileipellis, which is a transition between an epithelium and a hyphoepithelium. In addition, we have observed cheilocystidia in L. fuscomaculatus collections, while they are completely absent in L. rubrobrunneus.
Fig. 1 The obtained ML phylogeny based on ITS sequences. Names in boldface are new species. Names in blue are obtained from public databases. Bootstrap values and posterior probabilities are indicated if they exceed 50% and 0.85, respectively. The bar scale represents the expected number of nucleotide changes per site.