Eucommia jeffersonensis

Eucommia jeffersonensis is an extinct species of flowering plant in the family Eucommiaceae. It is known from a fossil fruit found in latest Eocene deposits of Oregon, United States. E. jeffersonensis is one of five described fossil species from North America assigned to the modern genus Eucommia. The other species are E. constans, E. eocenica, E. montana, and E. rolandii.

Eucommia jeffersonensis is known only from a single fossil, the holotype, specimen UF 11053, which is housed in the paleobotanical collections of the Florida Museum of Natural History. The specimen, a partially complete mature fruit, is preserved as a compression fossil in lacustrian shale recovered from the Gray Butte flora exposed near the base of Gray Butte in Oregon. The Gray Butte fora was formerly considered part of the youngest Clarno Formation and plants found almost exclusively in the Clarno formation are present at Gray Butte. The flora also hosts plants almost exclusively in the John Day Formation that overlies the Clarno Formation, and has more recently been considered part of the John Day Formation. Fossils from the similarly aged White Cap Knoll location in Wheeler County, Oregon have been assigned to E. montana, which indicates at least two species of Eucommia were present in Oregon during the latest Eocene.Eucommia jeffersonensis was first studied by paleobotanists Victor B. Call and David L. Dilcher, both of the University of Florida in Gainesville. Call and Dilcher's 1997 type description of the new species was published in the botanical journal American Journal of Botany. The specific epithet jeffersonensis was chosen as a reference to Jefferson County, Oregon where the Gray Butte Flora outcrops and the species type locality is.