This species can be recognized by its robust habit, leaves that are white-canescent below, stipules that are so deeply divided they appear to be four free stipules, and large inflorescences with rather large white flowers that are bearded or densely hairy at the throat. The flowers are apparently nocturnal, and presumably pollinated by moths. This species is widespread and rather variable in morphology, and one of the more frequently encountered species Isertia.
This species is similar to Isertia hypoleuca, and these have sometimes been confused (most notably by Dwyer in the Flora of Panama Rubiaceae). These species both have robust habits, leaves that are white-canescent below, and flowers of similar size and form. However I. hypoleuca has red to yellow flowers and drupaceous fruits with 5-6 locules, vs. berries 2-3 locules in I. laevis. Isertia laevis is also similar to I. pittieri, in particular in its robust habit and large white flowers; however I. pittieri differs in its leaves that have gray or transparent pubescence on the lower surface and slightly longer corollas.