Systematics and evolution of breeding systems in Gaertnera (Rubiaceae)

This thesis includes a systematic revision, phylogenetic analysis and study of breeding system evolution in the angiosperm genus Gaertnera (Rubiaceae or Coffee family). The systematic revision synthesizes field studies in Brunei Darussalam, Madagascar, Malaysia, Mauritius, Sri Lanka, and Singapore and analysis of more than 3500 herbarium specimens. The systematic revision recognizes and describes 68 Gaertnera species. Nineteen Gaertnera species are described as new. Distribution maps are presented for 71 taxa and 37 taxa are illustrated. A phylogenetic estimate of 30 Gaertnera species and related genera is inferred from nucleotide sequence variation in four nDNA markers: internal transcribed spacer (ITS), phosphoenolpyruvate carboxylase (PepC-Large and PepC-Small) and triose phosphate isomerase (Tpi). Counter to expectations based on the morphological variation and geographical range of the genus, the molecular phylogeny suggests that Gaertnera evolved both recently and rapidly. Molecular clock analyses estimate that Gaertnera radiated within the last 8--13.5 million years. This analysis tropical distribution and self-incompatibility breeding system. Phylogenetic character evolution studies are used to test the prediction derived from the loss of long-tongued pollinator hypothesis that dioecious species have significantly shorter corolla tubes than their distylous ancestors. Maximum likelihood and generalized least squares ancestral state reconstruction analyses produce very similar results. Both analyses support the prediction that dioecious species have shorter corolla tubes than their distylous ancestor, however, several distylous species also have shorter corolla tubes than their distylous ancestor. This is not predicted and suggests that additional studies are required to fully test whether the evolutionary scenario proposed by the loss of long-tongued pollinator hypothesis is supported. This is the first phylogenetic test of hypotheses proposed for the evolution of dioecy in distylous taxa and highlights both the utility and limitations of character reconstruction methods in taxa that have radiated rapidly.