A phylogenetic study of the South African representatives of the tribe Andropogoneae (Poaceae)

English: The tribe Andropogoneae makes up half of the grass subfamily Panicoideae, with approximately 85 genera and 960 species (Hartley 1958, Clayton and Renvoize 1986). The genera of the tribe are typically tropical with only a few species extending beyond the tropics into warm temperate regions. From information available it is clear that the African representatives form an integral part of the tribe. In this study we only concentrated on the South African representatives of the tribe. The tribe Andropogoneae has been studied extensively over the last millennium, but there is still an uncertainty about the true basic chromosome number. Previous molecular studies include sequencing of the ndhF, GBSSI and phytochrome B. The morphological variation in the tribe provides an interesting context to examine. This study focused on the sequencing of plastid chloroplast gene trnL-F and nuclear ribosomal DNA the Internal Transcribed Spacer (ITS) to determine the phylogenetic relationships within the tribe. In this study the chromosome numbers of 58 specimens were determined. The genetic chromosome numbers varied with n = 5, 9, 10, 10, 11, 20, 30. For the first time the basic diploid number of n = 5 was observed in the genus Andropogon. Urelythrum aggropyroides was studied for the first time with a somatic chromosome number of 2n = 20. The absence of multivalent and prevalence of bivalents in this study indicate that the genomes of the specimens studied are homologous. This lead us to the conclusion that the tribe consists of allopolyploid species, derived from interspecific hybridization and chromosome doubling. Both the trnL intron and trnL-F intergenic spacer was sequenced. Analysis of the trnL-F gene included 56 accessions and 61 accessions for the ITS gene. Combined analysis of both ITS and trnL-F included 59 accessions. Sequencing data indicated Cymbopogon to be a diploid progenitor of Hyparrhenia and Andropogon of Bothriochloa bladhii. Reticulate evolution was demonstrated in nrITS alleles. ITS and trnL-F data supports the inclusion of Arundinella in Andropogoneae and rejects the subtribal classification of Clayton and Renvoize (1986). This data also does not support the division of the tribe into awned and awnless genera and does not support the “core Andropogoneae” lineage as previously been observed. Most genera in the tribe are polyphyletic, suggesting a much more complex nature for the South African representatives. Molecular data could not prove the basic chromosome number but supported the maturity of the polyploid complex for the South African specimens.