First macrofossil record of Icacinaceae in East Asia (early Oligocene, Wenshan Basin) and its ecological implications

Icacinaceae are well represented in the modern tropical flora of East Asia, but this family has no confirmed macrofossils from this region. Most of the unambiguous fossils (e.g., endocarps) are from the Paleogene of North America and Europe, where the family is no longer present. Here we report a fossil endocarp of the liana genus Iodes from the Oligocene Wenshan flora, southwestern China. The fossil is relatively large (ca. 20 mm length, 11 mm width) and documents a vascular bundle inside the endocarp wall, a pattern of ridges enclosing few areoles, and an asymmetrical apex and rounded base. On the basis of these characteristics, we described a new species, Iodes elliptica, which represents the first Icacinaceae fruit fossil record from Asia. This fossil, consistent with recent reports of Iodes pollen from the Eocene of Hainan, indicates a long-standing presence of the genus in SE Asia, dating back to the Paleogene. Based on the climatic data of modern Iodes, and other fossil occurrences from Wenshan, we hypothesize that the climate in the region was subtropical during the Oligocene, supporting a rainforest, with an overall mixed regional flora of subtropical and tropical elements.

Automated summary

The fossil endocarp of the liana genus Iodes from the Oligocene Wenshan flora in southwestern China represents the first Icacinaceae fruit fossil record from Asia, indicating a long-standing presence of the genus in SE Asia, dating back to the Paleogene. Based on the characteristics of the fossil and climate data, it is hypothesized that the region had a subtropical climate during the Oligocene, supporting a rainforest with a mixed regional flora of subtropical and tropical elements.