Abstract/Summary

Heteropogon and Themeda grasses are common and significant components of the C4 savannas which have recently gained more attention for conservation and biodiversity research. The two genera have been the subject of ecological research due to their widespread and dominant species H. contortus and T. themeda. Like many tropical plant lineages, however, in-depth knowledge necessary for the management of these ecosystems is still lacking. This thesis focuses on the diversity of Heteropogon and Themeda in respect to evolution, ecology, and systematics. In this thesis, phylogenetic analyses indicated that the evolutionary history of Heteropogon and Themeda is being driven by complex evolutionary processes and their origin is dated back to the Miocene grassland expansion. I interpreted those discordant phylogenetic placements between plastid and nuclear trees as underlying polyploidization or hybridization within the groups. Dating analyses indicated that most species originated in the Miocene grassland expansion. Widespread species, H. contortus and T. triandra did not originate until the Late Miocene and quickly spread throughout the Tropics in the Pleistocene. Climatic niche characteristics and geographic distributions of Heteropogon and Themeda shed light on macroecological patterns, adaptation by functional traits, and the evolution of climatic niche and functional traits. I found that Heteropogon and Themeda species are separated into savanna and wetland groups. This is supported by differences in precipitation regimes of the two habitats and functional traits (e.g., plant height, leaf area, and awns). In an evolutionary context, biomes were shifted from savannas to wetlands, and niche divergence occurred. Functional traits changed by habitat preferences and show lability in the lineage. Integration of morphology and new ecological and phylogenetic evidence derived from this thesis were used in new generic and species reclassifications of Heteropogon and Themeda. I conclude that the generic description of Heteropogon should be narrowed, and I accept three species, while that of Themeda expanded to accept 26 Themeda species and 2 varieties. Phylogenetic relationships determine diagnostic morphological characters in generic and species delimitations. This new systematics of Heteropogon and Themeda demonstrates how to apply various biological data in taxonomic revision, and to summarize biodiversity information of Heteropogon and Themeda.