This species is characterized by its somewhat small leaves, spiciform inflorescences with up to ca. 1 dozen sessile flowers, small entire to denticulate involucels, lobed calyx limbs 5.5-6 mm long, and bright pink to red corollas with tubes 17-21 mm long and the tubes longer than the those. The leaves are elliptic to ovate, have closely reticulated but not very prominent veination. This species has been infrequently collected.

Retiniphyllum glabrum is similar to Retiniphyllum discolor, which Cortés-Ballén (2003) separated by its calyx limbs 8-8.5 mm long and corolla tubes 14.5-16 mm long. Both of these are similar in general to Retiniphyllum schomburgkianum and several related species, but those all have white to pink corollas with tubes 10 mm long or shorter and the lobes longer than the tubes. These first two species are also similar in general to Retiniphyllum maguireorum and Retiniphyllum tepuiense, with pedicellate flowers.