Aesculus

A very easily recognized genus, with its opposite, palmately compound leaves and distinctive fruit. The latter is a capsule, the outside ± prickly (in our species) and only 1 or occasionally 2 (very rarely more) large seeds developing within. The seed has an unusually broad pale scar (hilum) representing the area of attachment; the rest of it is a shiny rich reddish brown when ripe.

Other species of Aesulus are cultivated for ornament, and A. parviflora Walter; a late-blooming shrub with a slender inflorescence with pure white petals and  long-exserted stamens several cm long is known to escape in adjacent Ontario and Ohio.

1. Leaflets 5, tapered ± gradually to tip; winter buds not glutinous; hilum not over 1/2 as broad as the diameter of the seed; flowers yellowish green.

A. glabra

1. Leaflets mostly 7, abruptly acuminate to a short tip; winter buds very glutinous; hilum about two-thirds or more as broad as the seed; flowers white.

A. hippocastanum