The mushroom is characterized by a stout fruit body with a smooth and sticky orange cap up to 7 cm (2.8 in) in diameter.

The epithet rupestris refers to the campos rupestres montane savanna—the ecoregion where the type species was collected.

For example, although L. rupestris has several characteristics that make the section Edules proposed by Annemieke Verbeken a somewhat close match,[2][3] the taxon cannot be included because the surface of its cap is neither sufficiently areolate (cracked) nor dry enough, and its spores are excessively ornamented in comparison.

The ornamentation on the spore surface is amyloid (staining blue to blue-black in Melzer's reagent) and finely wart-like, with each wart ranging to 0.5–0.7 μm high.

The hilar appendage (the part of a spore once attached to the basidium via the sterigma) ranges in shape from narrowly obtuse to somewhat conical; the plage is not very distinct, but has an amyloid spot.

The edge of the gill is sterile (lacking basidia), and has marginal cells that are 30–45 by 4–6 μm, cylindrical to somewhat sinuous (curvy), thin-walled, and hyaline (translucent).

[1] The mushroom was found buried with up to two-thirds of the stem in sandy soil near several shrubs (Fabaceae, subfamily Mimosoideae and others) in a semi-arid region, after heavy precipitation.

The species is known only from the type locality in Vale do Catimbau National Park in Brazil, in the state of Pernambuco.

Although the fungus is suspected to be mycorrhizal (like all Lactarius), there was a wide diversity of plant species growing in the open, dry forest where the mushroom was found (including members of the tree families Euphorbiaceae, Fabaceae, Myrtaceae, Nyctaginaceae, and Polygonaceae—all known to form mycorrhizal associations), so the authors did not speculate on any specific interactions.