A primitive Cupuliferae plant (Trigonobalanus verticillata) found in Xishuangbanna, Yunnan, and its biogeographical significance

A primitive Cupuliferae plant (Trigonobalanus verticillata Forman) was found in Xishuangbanna, Yunnan, China. This plant species is considered as ancestral to the modern genera Quercus and Fagus. It has been recorded in Indonesia and Malaysia, as well as Hainan Island of China. Its discovery in Yunnan might provide a reasonable explanation for its distribution in Hainan Island and support the hypothesis that Hainan Island may have been adjacent to northern Vietnam and Guangxi in geological history.