Complex evolutionary history of two ecologically significant grass genera, <i>Themeda</i> and <i>Heteropogon</i> (Poaceae: Panicoideae: Andropogoneae)

Abstract Themeda and Heteropogon are closely related grass genera frequently dominant in tropical C4 grasslands. Relationships between them poorly resolved, impeding ecological study, especially of T. triandra with a broad distribution from Africa to East Asia, H. contortus pantropical distribution. Our analyses plastome nuclear genomes comprehensive sampling demonstrate that neither genus is monophyletic as currently circumscribed. Plastome data place melanocarpus ritchiei Themeda. Nested quadrivalvis unica, demonstrating this widespread species more morphologically diverse than previously recognized. fischerianus nested contortus. The picture complex for triticeus sister the analysis Cymbopogon analysis. This incongruence plastid phylogenetic trees suggests hybridization Cymbopogon-related genome donors dating estimates Themeda–Heteropogon crown age at c. 7.6 Myr, consistent Miocene grassland expansion. diversified 1–2 Mya Pleistocene. These results establish foundation studying history these ecologically significant grasses ecosystems they form.