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A new species of Zelkova (Ulmaceae, Ulmoideae) with leaves and fruits from the Oligocene of South China and its biogeographical implications

A new fossil species of Zelkova is described from the Oligocene Ningming Formation of Guangxi, South China. Zelkova ningmingensis sp. nov. is characterized by leaves with craspedodromous venation pattern and drupaceous fruit type. The new species possesses elliptical to ovate leaves, bearing 7–12 pairs of secondary and simple toothed margin, as well as epidermal cells with straight or rounded anticlinal walls. The species is compared with extant and other fossil species hitherto reported of the genus. It is most similar to the living Zelkova schneideriana in the leaf gross morphology and epidermal characters, which may be suggested to be the ancestral type of Zelkova schneideriana. The discovery of Zelkova ningmingensis sp. nov. in Guangxi indicates that Zelkova has already existed in southern China as early as the Oligocene. In combination with Zelkova material from the Oligocene of Europe, it can be inferred that Eurasian Zelkova had begun to diversify by at least the Oligocene. Because China is the biodiversity centre of modern Zelkova, the fossil herein provides new insights into Zelkova biogeography.