Deciduous trees and large shrubs found in all three northern continents. Leaves opposite, composed normally of five or seven leaflets (occasionally three or nine) radiating from the end of a long, slender stalk. Flowers borne in often large panicles at the end of the current season’s growth; petals four or five. Fruits sometimes prickly, sometimes smooth, containing one or two large seeds. Several of the following species are commonly known under the generic name of Pavia, the distinguishing characters being smooth fruits and four petals, as contrasted with the prickly fruits and five petals of true Aesculus. As in neither case are the characters invariably coexistent, the name Pavia has been dropped.
Few groups of woody plants are at once so well marked and so handsome as this. They all thrive well in the southern half of England, and most are hardy enough to succeed in any part of the country. All of them like a good deep soil, well drained but moist, and are easy to cultivate and transplant. For the multiplication of the species seeds are decidedly the best, but the hybrids and varieties of garden origin have to be propagated by budding. The common horse-chestnut is commonly used as a stock for all species, even such a small one as A. pavia, the result of which is an ungainly union of stock and scion and frequent ill-health. It may be used for A. × carnea (although that comes largely true from seed), and for its own numerous varieties, but for the other and smaller hybrids A. flava or A. glabra should be used as a stock. It should be mentioned that the buds selected are not those in the axils of the leaves, but the small, crowded buds at the base of the shoot nearest the old wood, which in ordinary circumstances remain dormant. Seeds of all the species should be planted as soon as they fall, and it is necessary to cover them only with about their own depth of soil. Kept dry during the winter, they lose much or sometimes all of their vitality.
In addition to the hybrids described below many others of natural origin in N. America have been identified, such as A. × mississippiensis Sarg. and A. × bushii Schneid. These hybrids are very confusing and difficult to distinguish and of little importance horticulturally.
From the Supplement (Vol. V)
The most important treatment of the taxonomy of Aesculus is that provided by James W. Hardin in ‘Studies in Hippocastanaceae’: Part II (Taxonomy of American species), Brittonia, Vol. 9, pp. 173-95 (1957); Part IV (Hybridisation), Rhodora, Vol. 59, pp. 185-203 (1957); Part V (Old World Species), Brittonia, Vol. 12, pp. 26-38 (1960).
For propagation see: P. McMillan Browse, ‘Propagation of the Hardy Horse Chestnuts and Buckeyes’, The Plantsman, Vol. 4, pp. 150-64 (1982). And for a general survey: David Wright, ‘Aesculus in the Garden’, The Plantsman, Vol. 6, pp. 228-47 (1985).