Thesis (Ph.D.)--Chulalongkorn University, 2007

A taxonomic study of subtribes Ischaeminae and Rottboelliinae in Thailand was carried out. Thirteen genera, 49 species and two infraspecific taxa are enumerated. Ischaemum (13 species and one infraspecific taxon) and Eremochloa (11 species) are the two largest genera. One new combination in Andropogon L.: I. tenuifolium (A. Camus) P. Traiperm & T. Boonkerd is made. A variety, I. barbatum Retz. var. glaberrimum Bor is treated here as a synonym of I. barbatum Retz. In addition, five taxa of Ischaemum namely, I. aristatum subsp. imberbe var. imbricatum, I. aristatus var. arfakense, I. lacei, I. magnum and I. macrurum are lectotypified. It was found that two taxa, i.e. Ischaemum hubbardii Bor and Mnesithea striata (Nees ex Steud.) Koning & Sosef. var. pubescens (Hack.) S.M. Phillips & S.L. Chen are new records. Six species in Ischaemum, Eremochloa and Mnesithea are new to science. Keys to the subtribes, genera and species together with descriptions, line drawings, photographs and distributional information of each species are given. Epidermal peels and transverse sections of leaf-blades and culms were investigated in 25 species of the 12 genera from the two subtribes. It is evident that anatomical features are taxonomically useful for generic delimitation. Phylogenetic analyses of 44 samples from 38 taxa were carried out using non-coding chloroplast DNA trnL intron, and trnL-F intergenic spacer sequence data together with nuclear ribosomal internal transcribed spacer (ITS) sequence data. Maximum Parsimony analyses were conducted using PAUP* 4.0b10. It was found that combined ITS and trnL-F analyses strengthen the phylogenetic signal and reveal that both subtribes are not monophyletic. The combined data also reject the monophyly of the genera Ischaemum and Mnesithea but provide evidence to show that Hemarthria, Hackelochloa and Eremochloa are monophyletic.