This species is characterized by its tree habit; robust, petiolate, broadly obovate leaves that are densely hirtellous below, cymose multi-flowered inflorescences with bracts 1-2 mm long, 5-(6-)merous flowers, funnelform corollas about 5-6 mm long, and woody capsules 3--5 cm in diameter. The specimens generally dry with a purplish brown or reddish purple color. The higher-order leaf venation is regularly developed, and the leaves are often bullulate. The blades are truncate to shortly cordate at the base. No calycophylls have been seen or described for this species. The calyx limb is 1-2 mm long and shallowly lobed. The corollas are green, with the lobes ca. 1 mm long. The stipules are, as is characteristic for Simira interpetiolar and convolute with each other, so they are twisted around each other into a conical structure; the illustration presented by Steyermark (1974: 346, fig. 56) is a little misleading, because it appears to show stipules similar to those of Hippotis, where the stipules are valvate and the structure formed by the who of them is twisted. Lateral buds on several specimens are unusual for Rubiaceae, with the pair of stipules that covers the young leaves subtended, or enclosed at the base, by shorter pair of leafless stipules.

Steyermark (1972, 1974) recognized three varieties of Simira erythroxylon, which he separated by pubescence details, leaf size, and number of secondary veins. These are also allopatric and differ in habitat, with the exception of one specimen he included in var. erythroxylon that falls in the range of var. meridensis. He did not know the flowers of his two new varieties. Steyermark included the plants from humid lowland forest in northern Venezuela in var. erythroxylon, one specimen from seasonal forest in the Orinoco basin of eastern Venezuela in var. saxicola, and plants from cloud forest in western Venezuela in var. meridensis. Taylor (Taylor et al., 2004) took a skeptical view of this taxonomy, and included var. saxicola in Simira rubescens; however further study with additional specimens shows that actually, these plants are best regarded as a separate species. Var. saxicola dried green or brownish green, has leaves with soft whitened pilosulous pubescence, a longer calyx limb than the typical form of this species, ca. 4 mm long with a leathery basal part, and corollas ca. 8 mm long with acute lobes that are about as long as the tube and have a thickened tip, and is known from granitic outcrops. Steyermark's var. meridensis is also re-evaluated here, and circumscribed differently; these plants are better known now, and probaby better treated as a separate species. One specimen collected at 3450 m in Mérida was included by Steyermark in var. erythroxylon; this has not been seen, and is provisionally excluded here from that variety and perhaps from this species. The type of var. meridensis has also not been located, so this name is used here provisionally based on other collections identified by Steyermark as this variety.

Ironically, the epithet "erythroxylon" has been applied independently to two different species of Simira by two separate authors, and these two species are generally similar. The other use of this epithet was for a species from western Ecuador and Peru, now called Simira ecuadorensis; this western South American species differs from Simira erythroxylon var. erythroxylon in its larger flowers, with corolla tubes 8-9 mm long, that spread at anthesis into a patelliform skirt and stigmas 7-10 mm long. The plants that Steyermark treated as Simira erythroxylon var. meridensis are similar to Simira standleyi, see comments under that variety. The plants included in Simira erythroxylon var. saxicola are similar to Simira rubescens, which has leaves that usually have well developed domatia and are glabrous or coarsely and irregularly strigillose to strigose or hirtellous below and corollas with short rounded lobes.

• Steyermark, J. A. 1974. Rubiaceae. 9(1–3): 7–2070. In T. Lasser (ed.) Fl. Venezuela. Fondo Editorial Acta Científica Venezolana, Caracas.
• Steyermark, J. A. 1972. Rubiaceae. 23: 227–832. In B. Maguire & Collaborators (eds.) Bot. Guyana Highl.—Part IX. Mem. New York Bot. Gard. New York Botanical Garden Press, Bronx.
• Taylor, C. M., J. A. Steyermark, P. G. Delprete, A. Vincentini, R. Cortés-Ballén, D. C. Zappi, C. H. Persson, C. B. Costa & E. Anunciação. 2004. Rubiaceae. 8: 497–847. In J. A. Steyermark, P. E. Berry & B. K. Holst (eds.) Fl. Venez. Guayana. Missouri Botanical Garden Press, St. Louis.