Their leaves are oppositely arranged, small, sessile or sub-sessile, and possess inconspicuous secondary venation.

Flowers are tetra- or pentamerous, with the stamens adnate to the white or pink funnelform or salverform corolla.

[4][5] The remaining species are most closely related to the North American and Caribbean genus Houstonia (including Stenaria) and one species of the polyphyletic genus Oldenlandia (Oldenlandia microtheca) distributed in Mexico and Central America, indicating that Arcytophyllum may be one of the few cases in the family Rubiaceae of a southward migration to reach the Andes.

[6] Flowers of Arcytophyllum are distylous, meaning that two morphs exist differing in the vertical orientation of anthers and stigmas.

If pollinators promote the condition of distyly and asymmetric pollen flow over evolutionary time, it is plausible that gender specialization will evolve into dioecy.