This species is widespread in wooded vegetation on both lateritic and quartzite substrates and has been collected in the grasslands of the central plateau. The MO specimens are on loan so the identifications have not been all recorded, and the distribution given here is provisional. Oldenlandia herbacea is similar to Oldenlandia lancifolia, and these species are often confused; Oldenlandia herbacea has been much more commonly collected in Madagascar.
Bremekamp (1952) and Verdcourt (1976) both recognized several varieties of Oldenlandia herbacea, with all but var. herbacea restricted to Africa. Many of the Madagascar plants match var. herbacea in their corolla tubes 2-4 mm long and glabrous smooth calyx and ovary, while some match var. papillosa in having a corolla of similar size but a sparsely pubescent calyx and ovary; these varieties do not seem useful to separate in Madagascar.
!CMT, V 2011