|Keywords:||Gentianaceae – Evolution; Gentianaceae – Morphology|
|Full text PDF:||http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000051029|
Chelonanthus is a widespread and common neotropical angiosperm genus in the tribe Helieae (Gentianaceae), a group known for its high morphological and ethnobotanical diversity. This genus has been riddled with taxonomic confusion for the last 150 years, and this is the first detailed study ever published on its morphology, evolution, and speciation. Molecular and morphology-based phylogenies of the tribe Helieae reveal a polyphyletic condition with Chelonanthus divided into two strongly separated lineages, one containing the purple-flowered type species Chelonanthus purpurascens and the other containing all other species, which have green to white corollas. This green-white corolla clade contains the most common and widespread species, Chelonanthus alatus, a polyphyletic species complex composed of six morphological variants. This dissertation sampled all recognized species of Chelonanthus as well as all morphological variation found in Chelonanthus alatus. The analytical tools of phylogenetics (Parsimony and Bayesian Analyses) and morphometrics (Principle Component Analysis) were combined to resolve inter- and intra-generic relationships between Chelonanthus and closely related genera of Helieae as well as define species boundaries within the species complex of Chelonanthus alatus. The presented phylogeny, based on 5S-NTS and ITS data, together with a Principle Component Analysis of morphological characters, supports the need to recircumscribe and rename this polyphyletic genus and segregate four of the six morphotypes of Chelonanthus alatus as four segregate species. Two new species will be described, Chelonanthus hamatus found in the Guayana Highlands of French Guiana and Venezuela and Chelonanthus pterocaulis found in Central America, Trinidad and northeastern South America from Costa Rica to French Guiana. Two typified names associated with the Chelonanthus alatus species complex, Chelonanthus acutangulus and Chelonanthus grandiflorus also will be resurrected. In addition, a new species of the previously monotypic genus Sipapoantha (Helieae) will be described from northeastern Brazil. The new knowledge of this group was included in the floristic treatments of Chelonanthus for the Flora of the Guianas and the Catalogue of Vascular Plants of Bolivia.