A New Clue for the Late Eocene Freshwater Ecosystem of Central China Evidenced by New Fossils of L. and Miki (Lythraceae).

Both L. and the extinct Miki are aquatic plants in the family Lythraceae, with abundant fossil records in Eurasia and North America in the Cenozoic. However, documented materials are mainly based on fruit and pollen grains without reliable leaf fossils. Here, we report fossil leaves, fruit, and roots of and fruit of from the late Eocene of Weinan, the Weihe Basin of central China. The fossil leaves are identified as a new species, Z. C. Han et H. Jia sp. nov., which represents the earliest known record of a leaf fossil. It is remarkably similar to extant species of , mostly due to the unique inflated petiole structures found in both of them. While displaying prominent intergeneric differences, the incomplete fossil fruits are assigned to sp. indet. and sp. indet. The former is the earliest fossil fruit record of , and the latter represents the earliest fossil record of found in Asia. These new fossil discoveries suggest that the divergence of and occurred at least by the late Eocene. It is believed that modern most likely originated in China. Furthermore, this unexpected aquatic plant fossil assemblage indicates that central China was warm and humid, with freshwater ponds or lakes, in the late Eocene and not as arid as previously thought.