The common horse chestnut, Aesculus hippocastanum, is a large, deciduous flowering tree. It is most commonly cultivated throughout temperate zones. Urban tolerant, the common horse chestnut is widely used as a street and shade tree. Palmately compound leaves with seven obovate leaflets, a spiny fruit and dark brown sticky buds characterize this species.
According the to the United States Department of Agriculture (USDA), the red horse chestnut, Aesculus X carnea, is a hybrid of Aesculus hippocastanum (common horse chestnut) and Aesculus pavia (red buckeye). Research at the University of Connecticut suggests that the species probably originated as a chance hybrid made by insects in 19th century Germany.
According to the University of Connecticut (UCONN), the ruby red horse chestnut, Aesculus x carnea ‘Briotii', is slightly smaller than the red horse chestnut. The ruby red horse chestnut has larger flower clusters and a deeper red flower color. The most popular cultivar of this species, the ruby red is less susceptible to fungal disease than other Aesculus.
Aesculus hippocastanum ‘Baumanii’ is a cultivar of the common horse chestnut. This species has double white flowers that do not produce fruit. Many believe the lack of fruit is an improvement over the other species (no fruit mess).
The Japanese horse chestnut, Aesculus turbinata, is an ornamental tree native to Japan. Introduced to North America in the late 19th century, the Japanese horse chestnut has larger leaves than the common horse chestnut and is widely planted as an ornamental. A beautiful specimen tree, the Japanese horse chestnut is tolerant of a wide range of soils and is often found in formal gardens.
Native to its namesake, the California horse chestnut, Aesculus californica, occurs in dry conditions of canyon and slope habitats. This species has a leathery, pear-shaped fruit and produces showy white and pale rose-colored flowers. A small tree, the California horse chestnut may only reach a maximum height of 30 feet.