Systematics of Echiochilon and Ogastemma (Boraginaceae), and the Phylogeny of Boraginoideae

Echiochilon, Ogastemma and Sericostoma are revised resulting in the recognition of 15 species of Echiochilon and one Ogastemma species. Several species are placed in synonymy and three new species are described, E. baricum, E. callianthum and E. cyananthum. The single species of Sericostoma is shown to be nested within Echiochilon. The plastid atpB gene was sequenced for Echiochilon and Ogastemma from the Old World and Antiphytum from the New World, plus for a selection of 33 other Boraginaceae taxa. They were analysed together with selected outgroup taxa to give a framework of the tribes of Boraginoideae. The analysis gave support for establishing the new tribe Echiochileae for Antiphytum, Echiochilon and Ogastemma, and for merging the traditionally accepted tribe Eritrichieae with Cynoglosseae. The ITS region was sequenced for all but one species of Echiochilon and for representatives of Antiphytum and Ogastemma. Phylogenetic analysis of Echiochilon revealed that the strongly zygomorphic-flowered species form a paraphyletic group. The morphological data gave results fairly congruent with the ITS phylogeny. Biogeographic interpretations of the ITS and atpB phylogenies indicated a trans-Atlantic dispersal of Antiphytum as the most plausible explanation to the Old/New World disjunction. Analyses using DIVA (Dispersal Vicariance Analysis) of the distributions of the Echiochilon species indicated an ancestor to Echiochilon with a wide distribution over northern Africa and Arabia to India