Lactarius aquosus H.T. Le & K.D. Hyde
MycoBank number: MB811741; Facesoffungi number: FoF006F34
Basidiocarps medium-sized. Pileus 21−37 mm diam., rather plane with depressed center to infundibuliform at maturity, typically darker colored in center and appearing more or less zonate near the margin; surface smooth, dry and glossy in moist condition, reddish brown (8E8) in center, reddish blond (5C4) to dark blond (5D4) to reddish brown (8D5), margin pale orange (5A3) to cream colored margin with short and inconspicuous striations, slightly crenulate. Lamellae subdecurrent to decurrent, 1−4.5 mm broad, crowded, with 2−4 series of lamellulae, cream to yellowish white (4A1−2) to light yellow (4A4), with light brown (7D6) discolorations in older specimens, yellowish brown (5D5) when bruised. Stipe 25−48 ×5−15 mm, cylindrical, hollow; surface smooth, rugose when old, often with short hairs and whitish pruinose at base, brownish orange (6C6) to light brown (6−7D6), darkening to brown (7E7) near base. Context 2−4.5 mm broad in pileus, pale yellow (3A3) to grayish yellow (3B4) to light grayish orange (6B−C4), unchanging when cut; smell strong, raphanoid; taste mild or slightly bitter and astringent. Latex watery, unchanging on exposure, moderately abundant, unchanging with 10 % KOH, unchanging on white tissue paper and on white cotton handkerchief. Macrochemical reaction no reaction on the context with 10 % KOH and with FeSO4. Basidiospores subglobose to broadly ellipsoid, 6.1−6.9−7.2−7.9(−8.0) × 5.4−5.9−6.2−6.9 μm; Q = 1.06−1.15−1.17−1.27 (n=60); ornamentation amyloid, composed of ridges up to 1 μm high, forming an incomplete to almost complete reticulum, with short ridges connected by finer lines which are blunt to subacute; isolated warts common; plage inamyloid. Basidia 48−52 × 12−16 μm, 4-spored, subclavate, sometimes bent near base, typically with needlelike to guttate contents. Pleuromacrocystidia 55−74 × 9−16 μm, abundant, subfusiform to subclavate with mucronate or moniliform apex, protruding up to 30 μm, with fine granules and needle-like contents. Pleuropseudocystidia 3−4 μm diam., not emergent, irregularly cylindrical, bent or curved near base; apex round or capitate. Lamellar edge heterogeneous, consisting of basidia, capitate to subclavate marginal cells 27−38 × 12−17 μm and cheilocystidia 34−58 × 8−14 μm, abundant, subfusiform, some irregularly curved, with mucronate to slightly moniliform apex, protruding up to 35 μm above the hymenium. Lamellar trama consisting of smaller and larger globose cells, septate hyphae and lactiferous hyphae. Pileipellis a cutis, 90−140 μm thick, consisting of parallel, repent and sometimes slightly erect hyphae.
Habitat: gregarious or scattered on slope, in montane tropical forest, with Fagaceae. Collections examined: THAILAND, Chiang Mai Province, Mae-on district, Mae Takraii National Park, Thepsaded Waterfall, alt. 1150 m, N18º55.32 E99º21.31, 01/06/2012, KW231 (holotype, GENT!, isotype, MFLU!); Chiang Mai province, Mae Teang district, Bahn Pha Deng village, alt. 900 m., N19º17.12 E98º44.00, 01/06/2004, LTH102 (GENT!, CMU!, SFSU!);—ibid. 05/06/2005, LTH262 (GENT!, CMU!, SFSU!).
Notes: Lactarius aquosus is easily recognized in the field by its smooth pileus surface, zonate cap and transparent latex. Microscopically, this species has incompletely reticulate basidiospores and a cutis as a pileipellis.
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.