Homozeugos is an andropogonoid savanna grass from central Africa. The monophyly of the genus is confirmed by both morphological and molecular (ITSI&II) data sets. Homozeugos fragile and H. katakton form a clade that is sister to the rest of the genus. Within the other clade, H. eylesii is basal to the rest with H. conciliatus, sister to H. huillense and H. gossweilerii in the terminal clade. A Geographic Information System (GIS) was compiled using 48 layers of spatial environmental data. Soil chemical, physical and color analyses were done on samples from every collection made for this study. These data were integrated with the distributions of the species to predict the species' possible distributions using coincidence of layers in the GIS. The spatial data were then integrated with the cladogram, using a new method described here, to determine the degree of correlation of different environmental parameters with cladogenesis. Mean monthly precipitation (for several months) and hours of sunshine (for several months) as well as temperature and dry season vegetation are correlated with cladogenesis in Homozeugos to varying degrees.

Key words: Geographic Information Systems, Homozeugos, Poaceae, Graminae, Agenium, speciation