A Biosystematic Study of the Interiores Species Group of the Genus Vernonia (Compositae)

Abstract

The taxa of the Interiores species group are treated as two species, one of which is divided into two subspecies.Vernonia missurica, a widespread taxon, has large flower heads (32-58 flowers per head), obtuse involucral bract tips, and a characteristic flavonoid Chromatographic profile.Vernonia baldwinii ssp.baldwinii, occurring throughout the Ozarks and Ouachitas, andV. baldwinii ssp.interior of the Central Plains possess smaller flower heads (17-34 flowers per head), acute or acuminate involucral bracts, and a different Chromatographic profile.Vernonia baldwinii ssp.baldwinii is distinguished from ssp.interior by the recurved involucral bract tips and by the possession of more flowers per head. Morphological data reveal that an intergradation zone exists between the population systems of the two subspecies along the edges of the Ozarks and Ouachitas. Although much gene exchange occurs between these two taxa, they maintain a level of genetic integrity that permits their ready recognition throughout wide ranges. All three taxa have a gametic chromosome number ofn = 17 and hybridize extensively with sympatric species.