This species is characterized by its short deciduous stipules that are spathulate and truncate to rounded with well developed deciduous glands along their upper margins, its medium-sized leaves that are subsessile to very shortly petiolate, subtruncate at the base, and have well developed crypt domatia, its pedunculate subcapitate inflorescences without enlarged bracts, its tubular short calyx limbs, its slenderly funneform corollas with the tube pubescent through most of its length inside and longer than the lobes, and its white subglobose fruits. It is generally similar to Rudgea cornifolia and Rudgea coronata.

Zappi (2000) circumscribed Rudgea guyanensis broadly, to include plants from the western Amazon basin that had been separated as Rudgea cephalantha. These plants are all similar, however the plants originally included in Rudgea guyanensis are found in the Guianas east-central Brazil and have shallowly lobed to undulate calyx limbs and somewhat robust flowers, with the corolla tube 15-16 mm long and the corolla lobes 6--7 mm long, while the Rudgea cephalantha form is found in southern Colombia, easten Ecuador, and eastern Peru and has calyx limbs that are divided almost to the base and smaller corollas, with the tubes 6-10 mm long and the lobes ca. 4 mm long. No material has been seen of this species from central or west central Brazil, so whether the floral difference represent the end ranges of clinal variation cannot be evaluate. Plants from the Guianas commonly have flowers or perhaps fruits that are galled similarly to those of Rudgea cornifolia, with a fusiform shape and a dividing line across the middle.