University of Missouri - Saint Louis

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An oral examination in defense of the dissertation for the degree

Doctor of Philosophy

Patrick W. Sweeney
M.S. Botany, 1999, University of Georgia.
B.S. Biology, 1994, Georgia Southern University.

Systematics and Floral Evolution in the Plant Genus Garcinia (Clusiaceae)

Abstract

The pantropical genus Garcinia (Clusiaceae), a group comprised of more than 250 species of dioecious, trees and shrubs, is a common component of lowland tropical forests and is best known by the highly prized fruit of mangosteen (G. mangostana). The genus exhibits extreme diversity of floral form as is found anywhere in angiosperms and there are many unresolved taxonomic issues surrounding the genus.

To understand patterns of floral evolution within the group and to evaluate morphology-based classification schemes involving Garcinia and its relatives, relationships among a broad sample of Garcinia and close relatives were inferred by conducting Bayesian, parsimony, and likelihood analyses of sequence data from two nuclear genes, granule-bound starch synthase (GBSSI) and the internal transcribed spacer (ITS). The phylogenies suggest that all species of Garcinia fall into two major lineages one of which is characterized by the occurrence of nectariferous floral structures of uncertain derivation such as antesepalous appendages and intrastaminal disks and rings and the other by their absence. Several additional clades are supported each sharing particular combinations of floral characters and which generally correspond to sections recognized in the most recent taxonomic treatment of the genus. These results support a broad circumscription of Garcinia to include the segregate genera Ochrocarpos, Pentaphalangium, Rheedia, and Tripetalum, and the monophyly of tribe Garcinieae is supported.

The nectariferous floral appendages, disks and rings that characterize one of the major lineages identified in the molecular phylogenetic analyses have been hypothesized to represent an outer whorl of stamens. The position of these structures in mature Garcinia flowers does not support this interpretation. To better understand the nature of theses structures in Garcinia, floral development and anatomy were studied in a sample of six Garcinia species. An outer whorl, staminodal origin for the disks and appendages is not supported by developmental timing or position. Disks and appendages are not apparent until late in development and the disks arise in the center of flower. Anatomical data is equivocal. These data also reject a gynoecial origin for these structures, and suggest that they are instead intrastaminal receptacular nectaries that are independent of the floral organs. Other notable features of floral development include open carpel development and interspecific differences in floral morphology being evident ab initio.

Defense of Dissertation Committee