Acer rousei is an extinct maple species in the family Sapindaceae described from a series of isolated fossil samaras. The species is solely known from the Early Eocene sediments exposed in south central British Columbia, Canada adjacent to northeast Washington state in the United States. It is the type species for the extinct monotypic section Rousea. Taxonomy Acer rousei was described from two complete fruit specimens which were recovered from outcrops of the early Eocene, Ypresian Allenby Formation exposed near Princeton, British Columbia and an additional three fruits from the Ypresian McAbee Fossil Beds near Cache Creek, British Columbia. The two Allenby Formation specimens were found at the Burke Museum of Natural History and Culture location UWBM B3389, known as the One Mile Creek locality. Both the Allenby Formation and the unnamed formation outcropping at the McAbee Fossil Beds preserve upland temperate floras that were first interpreted as being Microthermal, although further study has shown them to be more mesothermal in nature. The plant community preserved in the Allenby formation is a mixed conifer-broadleaf forest with large pollen elements of birch and golden larch, but also having notable traces of fir and spruce. In contrast the McAbee Fossil Beds site is mostly broadleaf pollen with alder and elm dominating, and may represent a successional forest involving multiple volcanic ash eruptions. The species was known only from the McAbee Fossil Beds and Princeton fossil localities when first described. A. rousei is among a number of Acer species described from the Princeton and related sites by Wolfe and Tanai. Both the Acer rousei holotype samara, number UWBM 56256 A,B and the paratype UWBM 54107 A,B are currently preserved in the paleobotanical collections housed at the Burke Museum of Natural History and Culture, part of the University of Washington in Seattle. They are from the Allenby Formation. The paratype UBCB 2401 is in the University of British Columbia collections while the paratypes TMP P83.39.586 A,B and TMP P83.39.585 A,B are in the collections of the Royal Tyrrell Museum of Palaeontology in Alberta. The last three paratypes are all from the McAbee Fossil Beds. The specimens were studied by paleobotanists Jack A. Wolfe of the United States Geological Survey, Denver office and Toshimasa Tanai of Hokkaido University. Wolfe and Tanai published their 1987 type description for A. rousei in the Journal of the Faculty of Science, Hokkaido University. The etymology of the chosen specific