Pileus 30-50 mm diam., convex to plane with an umbo, disc gradually depressed, papilla conical, persistent; surface smooth, somewhat leathery, azonate, pale reddish-brown, brownish to deep orange or pale brown, often paler towards margin; margin decurved to inrolled, often wavy. Lamellae subdecurrent to decurrent, close to rather subdistant (ca. 5-7 per cm at margin), lamellulae of different sizes, orangish-yellow, brownish after bruising. Stipe 30-65 × 5-8 mm, cylindric, concolorous to rather darker towards base, smooth. Context hollow, pale orange to light brown. Latex copious watery to milky white, unchanging. Odor not distinct but spicy when dry. Spore print whitish. Basidiospores 7.5-9 × 5.8-8 μm, (Q = 1.1-1.22), broadly ellipsoid; ornamentation amyloid, up to 0.6-0.8 (-1.2) μm high, reticulate or forming a partial reticulum, isolated warts present, plage not distinct; under SEM the ornamentation is composed of continuous, interconnected ridges, with some free extremes, bands with irregular lobate margin. Basidia 38-50 × 8-12 μm, subclavate to clavate, 2- to 4-spored with long sterigma (up to 8 μm long). Pleuromacrocystidia 50-80 × 7-12 μm, oblong to oblanceolate, acuminate to moniliform at the apex, somewhat emergent (up to 8 μm); with refractive contents. Pleuropseudocystidia subclavate to clavate, up to 8 μm broad, numerous. Lamellar edges fertile, with basidia and few cystidia. Cheilomacrocystidia 30-45 × 6-8 μm, clavate to fusiform, infrequent. Subhymenial layer up to 14 μm, cellular. Hymenophoral trama with sphaerocytes and hyphae, laticifers up to 10 μm broad. Pileipellis a hyphoepithelium, up to 70 μm wide, subpellis composed of subglobose to vesiculose cells, arranged in 5-6 layers, cells 12-22 × 8-15 μm; hyphal elements up to 5 μm broad, scarce.
Ecology: Lactarius mukteswaricus grows under Quercus leucotrichophora in subtropical to temperate deciduous forests in the Nainital district of Uttaranchal.
Notes: The present species is distinguished by its papillate and applanate pileus, and its rather stocky habit, unchanging watery white latex, basidiomes without any particular odor when fresh, but spicy when dry. Microscopically, the presence of macrocystidia is distinctive. Lactarius mukteswaricus is close to Lactarius camphoratus (Bull.: Fr.) Fr., but the latter has a spicy odor in fresh condition, crowded lamellae, and basidiospores having a different ornamentation pattern. The examined Belgian and Spanish specimens of L. camphoratus have basidiospores with isolated warts and ridges, at times connected by low bands but not forming a complete reticulum (cf. Heilmann- Clausen et al., 1998; Basso, 1999)