The genus Aesculus comprises 13-19 species of woody trees and shrubs native to the temperate northern hemisphere, with 6 species native to North America and 7-13 species native to Eurasia; there are also several hybrids. Species are deciduous or evergreen. Linnaeus named the genus Aesculus after the Roman name for an edible acorn.

Aesculus species are woody plants from 4 to 36m tall (depending on species), and have stout shoots with resinous, often sticky, buds; opposite, palmately divided leaves, often very large (to 65 cm across in the Japanese horse chestnut Aesculus turbinata).
Winter buds of some Aesculus-species excrete lipophilic material together with flavonoid aglycones. Besides nine flavonols found earlier in Aesculus hippocastanum, kaempferol 3,7-dimethyl ether is found to occur in Aesculus carnea and Ae. turbinata but not in Ae. indica, and kaempferol 3,7,4′-trimethyl ether only in Ae. turbinata.