Palicourea costularia is characterized by its dense pilosulous pubescence on vegetative and reproductive structures, with the stem trichomes spreading to weakly reflexed; medium-sized to rather small, petiolate leaves with relatively numerous secondary veins; laminar, deeply lobed stipules with parallel sides and narrowly triangular lobes; shortly pedunculate, subcapitate to shortly cymose inflorescences with the flowers subsessile in several heads and subtended by bracts 7--10 mm long; deeply lobed calyx limbs 5--5.5 mm long; tubular-funnelform, white to yellow corollas that are pilosulous externally with tubes 9--11 mm long; medium-sized, ellipsoid fruits that are weakly laterally flattened; and hemispherical pyrenes with four or five sharp abaxial ridges and a slender medial groove. The corolla lobes have a conical abaxial appendage 0.3--0.4 mm long. This species was illustrated by Steyermark (1974: 1342, fig. 211).

Palicourea costularia is similar to and apparently closely related to several other species that are also found in premontane to usually high-montane elevations in the northern Andes; see the page for Palicourea aschersonianoides for a key to these.