Fruits and seeds of Ruppia (Potamogetonaceae) from the Pliocene of Yushe Basin, Shanxi, northern China and their ecological implications

摘要

Numerous fruits and seeds of Ruppia are reported from the Upper Pliocene (2.3-3.5 Myr ago) Zhangcun Formation in Yushe Basin, Shanxi, northern China. They are the first fossil Ruppia from China and demonstrate the importance of fruit and seed fossils in recording genera not represented by fossil leaves. These Ruppia are characterized by possessing a small oval endocarp, smooth endocarp surface, distinct elliptical external depressions, distinct apical mucro, slightly curved seed shape and conspicuous globose hilum. A new species, R. yushensis Zhao, Collinson and Li, is described from these endocarp and seed features. Comparison with the two European Miocene species, R. palaeomaritima Negru and R. maritime-miocenica Szafer, indicates the existence at that time of three different geographical and stratigraphical species. R. yushensis constitutes the first Pliocene record of Ruppia and extends the range of fossils of this genus from Europe to eastern Asia. R. yushensis is the only aquatic plant in the uppermost middle part of the Zhangcun Formation. This monotypic occurrence indicates a brackish, clear, tranquil and shallow lake in this region in the Late Pliocene. The smooth endocarp surface further suggests a warm temperate or temperate palaeoclimate.