Ormosia (Fabaceae: Faboideae) from the Miocene of southeastern China support historical expansion of the tropical genus in East Asia

ABSTRACT

The development of the Asian monsoonal climate sparked a latitudinal shift in vegetation zones from the Oligocene to the Miocene. However, little is known about the history of the megathermal floristic response to the geologic events in key regions like subtropical China. Here, a species of Fabaceae, Ormosia cyclocarpa sp. nov., is recognised based on well-preserved fruits from the Miocene of Zhejiang in middle-subtropical China. This species features dehiscent, compressed suborbicular single-seeded pods with an intramarginal vein. Extensive comparisons with extant/fossil fabaceous taxa confidently support the present taxonomic consideration. Considering the extant distribution, diversity centre and regional climate history, the known fossil occurrences in southern China imply that Ormosia extended northwards during the Miocene from probable tropics of origin into subtropical China, where a once broad latitudinal arid zone prevailed throughout much of the Palaeogene. Such a changing phytogeographic pattern across tropical-subtropical China probably resulted from a drastic East Asian climate change around the Oligo-Miocene boundary, and closely coincided with the early-middle Miocene warming. The spreading of Ormosia and other tropical genera (e.g. Dipterocarpus, Shorea, Bauhinia, Dacrycarpus) sharing similar floristic history in subtropical China indicates a palaeotropical and Miocene origin for some clades of the extant East Asian flora.

KEYWORDS:

• Climate change
• fossil fruit
• geographical dispersal
• Papilionoideae
• southern China
• tropical forest component

Acknowledgements

We thank three anonymous reviewers and Dr. Gareth Dyke (Editor) for their constructive comments, Prof. Hang Sun (Kunming Institute of Botany) for assistance with fossil identification, Drs. Guanjun Hui and Junbiao Yu for field collection, Dr. Zixi Wang for providing some pictures of herbarium from the Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, and Drs. Hai Zhu, Ruiyun Li, Yuli Chen and Hongshan Wang for constructive discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work is supported by the National Natural Science Foundation of China (grant numbers 41972010, 41872017); the Natural Science Basic Research Program in Shaanxi Province of China (grant number 2019JM-401); the Foundation of State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) (grant numbers 193113, 183125); Opening Foundation of Shaanxi Key Laboratory of Early Life and Environments (Northwest University); and the China Scholarship Council for the financial support to X-CL (CSC grant number 201906565035).