Fossil fruits and a vegetative axis assignable to the extant genusCeratophyllumare described from four North American Tertiary localities. Fossil fruits assignable to the extant speciesC. muricatumandC. echinatumare reported from the Eocene Green River and Claiborne formations, and the Miocene Esmerelda Formation, respectively. An extinct species,C. furcatispinum, is described from the Paleocene Fort Union Formation and represents the oldest published report ofCeratophyllumin the fossil record. The existence of extant angiosperm species in the Eocene is very unusual and may be attributable in this case to slow evolutionary rates and unusual evolutionary properties associated with hydrophily in the genusCeratophyllum.