We tested the phylogenetic hypothesis that the circumscription of the genus Ipomoea comprises all members of Hallier's historical taxon, subfamily “Echinoconiae”, including Argyreia, Astripomoea, Lepistemon, Rivea, Stictocardia, and Turbina. Support for the paraphyly of Ipomoea was found based on phylogenetic analysis of 45 taxa using DNA sequences (the ITS region and three exons and two introns of the 3’ end of the nuclear gene waxy) in combination with morphological data. Two major clades within Ipomoea s. l. were resolved in the strict consensus of 16 most parsimonious trees. One clade included most of the smaller segregate genera interspersed with species of Ipomoea, whereas the other was formed by Ipomoea s.s. and Astripomoea. Our results also indicated the genus Turbina is polyphyletic and Rivea is nested within Argyreia. Together, these results suggest new phylogenetic interpretations and point towards a revised view of the nature of morphological evolution among these taxa. We used both our current understanding of morning glory systematics and the distribution of character state variation in seven taxonomically important characters to demonstrate that: 1) the common Ipomoea form is widely distributed, 2) the common form has given rise to specialized forms exhibiting a diversity of character state combinations, and 3) many of the specialized forms have arisen repeatedly. On the basis of these observations, we forward a general model of mosaic evolution that emphasizes extreme evolutionary lability in morphology among morning glory species.
Communicating Editor: John V. Freudenstein