The word Aesculus was borrowed from an old Latin word meaning “a variety of oak tree” or describes an oak that bears edible acorns. It first appeared in text in 1809. To be clear, Aesculus is not a variety of Quercus, the genus for Oak. The genus Aesculus has approximately 13 species of deciduous trees and shrubby plants from North America, Europe, and Asia. Species growing near other species of Aesculus hybridize readily, providing further variation and, at times, can make identification tricky.
In the United States, our native Aesculus are commonly called “buckeye,” a name derived from their shiny seeds’ resemblance to a deer’s eye. Another common name is “horse chestnut,” which arose from the belief that these trees were closely related to members of the edible chestnut genus Castanea. The leaf scar on Aesculus also resembles a horseshoe, which likely contributed to the origin of the name “horse chestnut.”
Aesculus is a part of the soapberry (Sapindaceae) family. It’s only distantly related to the Castanea genus.