Fossil Capsular Valves of Koelreuteria (Sapindaceae) from the Eocene of Central Tibetan Plateau and Their Biogeographic Implications

Chen, Pei-Rong; Del Rio, Cédric; Huang, Jian; Liu, Jia; Zhao, Jia-Gang; Spicer, Robert A.; Li, Shu-Feng; Wang, Teng-Xiang; Zhou, Zhe-Kun and Su, Tao (2022). Fossil Capsular Valves of Koelreuteria (Sapindaceae) from the Eocene of Central Tibetan Plateau and Their Biogeographic Implications. International Journal of Plant Sciences, 183(4) pp. 307–319.



Premise of research. Koelreuteria encompasses three extant species that are discontinuously distributed in East Asia and the Fiji Islands. Koelreuteria had a wide distribution in the Northern Hemisphere during the Paleogene, with the first known fossil record being from the early Eocene of western North America. This study reports early fossil occurrences of Koelreuteria in Asia with a detailed morphological investigation and considers the history of its biogeographical dispersal in light of these finds.

Methodology. Four capsular valve fossil species of Koelreuteria are recognized from the early middle Eocene of the Niubao Formation at the Jianglang site (present altitude 4850 m), Bangor County, central Tibetan Plateau, China. They are compared with previous fossil occurrences using existing literature and herbarium records of extant material.

Pivotal results. We describe a new species, Koelreuteria kvacekii P.-R. Chen, C. Del Rio & T. Su sp. nov., characterized by its oblate capsular valve, lobed apex, and cordate base of the valve, as well as one or two suborbicular seeds per locule. Other material is assigned to species previously described from other locations, extending the geographic and stratigraphic ranges for K. miointegrifoliola, K. allenii, and K. lunpolaensis.

Conclusions. Fossil records of Koelreuteria and other co-occurring plants evidence a subtropical climate in central Tibet during the middle Eocene, contrasting with the present cold and dry climate in this region. These are the earliest fossil records of Koelreuteria from what is now the Tibetan Plateau. It seems that the Tibetan region served as an early diversification center for Koelreuteria during the Paleogene in Asia. All species of this flora disappeared locally because of the formation of the Tibetan Plateau by the Neogene.

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