Systematics of Ruellia (Acanthaceae) in Southern South America

Ruellia comprises 23 species in southern South America, which display great diversification in flower and inflorescence morphology, presumably associated with a wide array of pollinators; this has resulted in the evolution of many different floral syndromes. It is suggested that this diversification could have evolved through heterochronic developmental changes associated with cleistogamy that produce morphological variation in flower form, selected by different types of pollinators. The generic limits of Ruellia are discussed in relation to this variation, and several generic names are considered synonyms, including Penstemonacanthus. Seven informal taxonomic groups of species are delimited: Chiloblechum, Dipteracanthus, Ebracteolati, Hygrophiloidei, Physiruellia, Ruellia, and Salpingacanthus