Aesculus has been reported previously from Tertiary deposits of the Northern Hemisphere based on isolated leaflet impressions, but corroborative data from complete, palmately compound leaves and from reproductive organs has been scarce. It is now possible to confirm this genus in the Paleocene of North America based on combined evidence from complete leaves, fruits and seeds. Fossil leaflets from the Paleocene of North Dakota, Montana and Wyoming that were previously assigned to the Juglandaceae as Carya antiquorum Newberry were transferred to Aesculus by Iljinskaya in 1968 based on her assessment of fossil leaflets described and illustrated in the literature. However, this transfer was largely overlooked by North American workers. Recently discovered complete, palmately compound leaves and associated trivalved fruits from the Fort Union Formation of North Dakota and Wyoming confirm that the fossils represent Aesculus. Each leaf has a long petiole with an expanded base and bears three to five obovate, sessile leaflets with finely serrate margins. Fruits are preserved as three-dimensional impressions in siltstone in association with these leaves at three localities: Little Bitter Creek and Rock Springs, Wyoming, and Trenton Hill, North Dakota. The fruits are trivalved, globular loculicidal capsules with spiny ornamentation. Globular seeds sometimes remain attached to the valves. Silicified seeds found with the leaves at Almont, North Dakota, correspond in seedcoat anatomy to extant Aesculus. The spiny ornamentation on the fruit valves matches that of A. glabra (eastern North America) and A. hippocastanum (eastern Europe); all other extant species are smooth or verrucate. The fossil species differs from extant Asian species by its spiny fruits, and its sessile, somewhat asymmetrical leaflets. These fossils indicate that the extant genus was already established by the late Paleocene in North America, complementing foliage remains from the Paleogene of Spitsbergen and Kamchatka and predating the Oligocene occurrences from mainland Europe.

Key words: Aesculus, fruits, leaves, Paleobotany, Paleocene, Tertiary