Casearia sylvestris var. sylvestris inhabits humid, dense forests, while var. lingua is restricted to xeric habitats, yet despite differences in morphology and habitat preference, intermediate forms exist in transitional environments, complicating the delimitation of the taxa. Cavallari et al. examine nine microsatellite markers and conclude that the two C. sylvestris varieties are relatively independent biological units, rather than representing the genetic continuum of a single species. Evidence for the existence of putative hybrid zones between these two varieties is also considered.