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

中文翻译：

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两个具有重要生态意义的草属 Themeda 和 Heteropogon（禾本科：Panicoideae：Andropogonae）的复杂进化史

Themeda 和 Heteropogon 是密切相关的草属，经常在热带 C4 草原中占主导地位。它们之间的关系没有得到很好的解决，阻碍了生态学研究，特别是对从非洲到东亚广泛分布的 T. triandra 和泛热带分布的 H. contortus 的研究。我们通过对 Themeda 和 Heteropogon 的全面采样对质体和核基因组的分析表明，这两个属都不是目前所限定的单系。质体和核数据将 H. melanocarpus 和 H. ritchiei 置于 Themeda 中。嵌套在 T. triandra 的是 T. quadrivalvis 和 T. unica，这表明这种分布广泛的物种在形态上比以前认识的更加多样化。Heteropogon fischerianus 嵌套在 H. contortus 中。对于 H. triticeus 来说，情况更为复杂，它是 H. triticeus 的姐妹。核分析中的 contortus 和塑性体分析中的 Cymbopogon。核和质体系统发育树之间的这种不一致表明 Cymbopogon 相关基因组供体和 H. contortus 之间的杂交。塑性体测年估计 Themeda-Heteropogon 冠龄为 c。7.6 Myr，与中新世 C4 草原扩张一致。Themeda triandra 和 H. contortus 在更新世使 1-2 Mya 多样化。这些结果为研究这些具有重要生态意义的广泛分布的草类及其形成的生态系统的历史奠定了基础。与中新世 C4 草原扩张一致。Themeda triandra 和 H. contortus 在更新世使 1-2 Mya 多样化。这些结果为研究这些具有重要生态意义的广泛分布的草类及其形成的生态系统的历史奠定了基础。与中新世 C4 草原扩张一致。Themeda triandra 和 H. contortus 在更新世使 1-2 Mya 多样化。这些结果为研究这些具有重要生态意义的广泛分布的草类及其形成的生态系统的历史奠定了基础。