This species is commonly encountered and widely distributed, and can be recognized by its short deciduous stipules 2-4 mm long (or rarely to 5 mm in Central America) that are spathulate and truncate to rounded with deciduous glands along their margins together with its medium-sized leaves that are subsessile to very shortly petiolate, subtruncate at the base, and have well developed crypt domatia; its cymose pedunculate inflorescences with regularly dichasial white axes that are usually articulate; its tubular calyx limbs 1-3 mm long; its white corollas with the tube 2.5-5 mm long and about equal to the lobes, which each have a distinctive short apical appendage; and its white subglobose fruits 4-7 mm in diameter with smooth pyrenes. The truncate base of the leaf blade is sometimes very narrow and easy to overlook. Specimens of Rudgea cornifolia occasionally have diseased inflorescences, with the flowers swollen into fusiform hard structures with the former ovary and former corolla portion each comprising about half of the gall. This is the most commonly collected and widely distributed species of Rudgea.

The identification of Rudgea cornifolia is generally straightforward except in the western Amazon basin, where either Rudgea cornifolia is unusually variable morphologically (e.g., Zappi, 2006) or there are several similar species that have not been been consistently separated. In Peru and Bolivia, the leaves of Rudgea cornifolia are smaller on average than in the rest of its range, and the calyx limbs 1-1.5 mm long. Plants from this region with larger fruits have been provisionally included by some workers in Rudgea cornifolia, but are here referred to Rudgea loretensis and Rudgea obesiflora. Some plants from this region have quite short inflorescences, 1-1.5 cm long including the peduncule, and agree with plants described as Rudgea mazanensis but these plants are not distinct from other plants of Rudgea cornifolia. Here plants from Peru with short inflorescences with the secondary axes as long as the primary axis, the flowers sessile to shortly pedicellate groups usually of three, and ellipsoid to ellipsoid-oblong fruits 7-10 mm long that are longitudinally ridged when dry are included in Rudgea loretensis.

Rudgea cornifolia is commonly confused with Psychotria and Palicourea because its stipules that are deciduous and additionally have distinctive glands that fall off before the rest of the stipule and are easily overlooked; Rudgea cornifolia is in particular similar in aspect to Psychotria horizontalis. Rudgea cornifolia is similar to several other species, in particular Rudgea isthmensis, Rudgea loretensis, Rudgea skutchii, Rudgea poeppigii, Rudgea killipii, Rudgea mazanensis, Rudgea costanansis, and Rudgea guyanensis; see their individual web pages for their distinctions.