Abstract
This dissertation examined the evolutionary relationships and evolutionary history of four endemic species of the genus Polyspora (= Gordonia) in Sri Lanka. Sri Lanka is part of the Western Ghats-Sri Lanka biodiversity hot spot with extraordinarily high species richness and endemism. In spite of its diversity and uniqueness, the biogeography of this region, especially of the flora, remains grossly understudied. My research aimed to fill this void by using the four endemic species of the genus Polyspora in Sri Lanka in phylogenetic, biogeographic, and morphological analyses. All four species of Polyspora in Sri Lanka are restricted to the wetzone of the country and they thereby represent the distribution pattern of a majority of the endemics of the country. These species have formerly been assigned to the genus Gordonia; however, recent phylogenetic evidence indicates that Gordonia is polyphyletic and that all Asian species should be included in either Polyspora or Laplacea. My research supports their inclusion in Polyspora, and I follow that nomenclature here. In Chapter 1, I review the geography, vegetation and floristics of Sri Lankan plants and present three hypotheses for their biogeographic affinities. I review evidence for each of these hypotheses from published plant molecular phylogenetic analyses. In Chapter 2, I use Ecological Niche Models (ENM) to test predictions on the distribution of Polyspora from Sri Lanka and the Western Ghats region of India, in the present, 65 years into the future, and during the last glacial maximum. Results show reciprocal areas of suitable habitat for species from Sri Lanka and the Western Ghats, so that Sri Lankan Polyspora could persist in the Western Ghats and vice versa. During the last glacial maximum, suitable habitats in the two regions were isolated, even though they covered greater area, extending into lower elevations, and despite the landbridge connecting Sri Lanka to the mainland. Projections into the future suggest dire conservation threats for Polyspora as the climate warms. In Chapter 3, I present a study of comparative anatomy of seed coat micromorphology in representatives of all three tribes of Theaceae using scanning electron microscopy. Results suggest fixed differences in each of the three tribes, supporting the polyphyly of the formerly recognized genus Gordonia and placement of Sri Lankan species in the tribe Theeae with Laplacea or Polyspora. Finally, in Chapter 4, I conduct phylogenetic analyses using plastid and mitochondrial DNA sequence that show species from Sri Lanka and India are most closely related to species from China in the tribe Theeae. These results support the renaming of Sri Lankan species from Gordonia to Polyspora. Analyses of three microsatellite markers from 114 individual plants from all four currently recognized species of Polyspora in Sri Lanka show differentiation between the morphologically distinct P. speciosa and sympatric populations of the remaining three species. Genetic structure also differentiates populations on the three major mountain ranges within Sri Lanka, but does not separate three species (P. ceylanica, P. dassanayakei, and P. elliptica) that occur on them.