Icacinaceae are a family of woody climbers, trees, and shrubs with a pantropical distribution. Although Icacinaceae are well represented in the modern tropical flora of East Asia, the fossil record of this family in this region is poor. 

In a study published in Journal of Systematics & Evolution, researchers from the Xishuangbanna Tropical Botanical garden (XTBG) reported a fossil endocarp and associated locule cast of Iodes from the early Oligocene Wenshan flora of Yunnan, southwestern China. 

The newly discovered unilocular fruit fossil is relatively large (about 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 the morphological characteristics showing features diagnostic of the icacinaceous genus Iodes, the researchers named the new fossil as Iodes elliptica for its distinctive elliptic shape that contrasts with other ovate-shaped Iodes fossil species. 

"To our knowledge, there are no published fossil fruit or endocarp records of Icacinaceae in Asia, making the fossil described here, Iodes elliptica, the first icacinaceous fossil fruit (and macrofossil in general) from the region," said Dr. SU Tao, principal investigator of the study. 

The fossil attests to a sub-tropical zone in East Asia during the Oligocene, insulated from the effects of the global cooling that began during the late Eocene. 

"As I. elliptica is present in the current center of Iodes diversification in Asia, this record reveals an ancient origin of some of the Southeast Asian tropical flora elements," added SU Tao. 

Fossil fruit and extant Iodes and habitat of extant Iodes. (Images by Cédric Del Rio)