Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology, Plant Systematics

Date of Defense

7-30-2008

Graduate Advisor

Elizabeth A. Kellogg

Committee

Cindy Dupureur, Ph.D.

P. Mick Richardson

Barbara A. Schaal

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 as 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 that 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. 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 these 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 are 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.

Included in

Biology Commons

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