Phylogeny and Evolution of Symbolanthus and Wurdackanthus (gentianaceae–helieae) in the Guayana Highlands and Andes, Based on Ribosomal 5s-nts Sequences1

Symbolanthus (Gentianaceae, Helieae) is a genus of small trees, shrubs, and herbs distributed in South America (the central and northern Andes and the Guayana Highlands) and southern Central America. To discover the pattern of Symbolanthus evolution and to assess the relationships between Symbolanthus and the closely related Wurdackanthus of the Guayana Highlands (Venezuela, Brazil) and the Lesser Antilles (St. Vincent), we performed cladistic analyses on members of both taxa. Molecular data (5S-NTS rDNA sequences) were gathered from individual plant samples, mainly from herbarium specimens. 5S-NTS sequence data did not resolve internal relationships well in Symbolanthus and show that the genus may be a recently and rapidly diverging clade. However, these results indicate that Wurdackanthus is either paraphyletic to Symbolanthus or that W. argyreus is nested within a Symbolanthus clade. Furthermore, W. frigidus may be the basalmost species of the Wurdackanthus–Symbolanthus clade. This species is noticeably divergent and distinct, molecularly and morphologically, from the rest of the clade. Testing an alternate phylogenetic hypothesis in which Wurdackanthus is monophyletic results in trees 11 steps longer than the shortest trees found, and still with Wurdackanthus nested within Symbolanthus. Ancestral morphological character evolution in the Wurdackanthus–Symbolanthus clade is discussed in the context of a 5S-NTS consensus tree.