So very cool that John shared photos of this species with me…. prior to his having done so, I had only known this plant from herbarium specimens. But: an interesting species it is! Ruellia bulbifera is part of the “Ebracteolati Clade” sensu Tripp (2007, Systematic Botany). In that clade, it is member to a strongly supported clade of other species that inhabit savannas, cerrados, or other areas subject to fire; these species often produce thickened lignotubers, from which plants re-grow following fire episodes.
Interestingly, this clade is geographically rich: some species are southern South American (such as R. bulbifera, R. beyrichiana, R. eriocalyx, R. hapalotricha, and R. magniflora), and others are Mexican / Central American (R. donnell-smithii). One, R. geminiflora, is widespread.
Wild collected, Bolivia, Darwin Initiative Project 16-004; Photo by John Wood