The European horse chestnut, Aesculus hippocastanum, is the horse chestnut most frequently used in herbal medicine. It is a member of the Hippocastanaceae family. Horse chestnuts are in an entirely different botanical family from the well-known sweet chestnut tree, Castanea vesca. Horse chestnuts exist in nature as both a tree and a shrub, and are found in all temperate regions of Europe, Asia, and North America.
There are 15 recognized species of horse chestnut. The European horse chestnut is believed to have originated in the Balkan region of eastern Europe but is now grown in every country in the Northern Hemisphere.
The name Aesculus is actually a misnomer, coming originally from the word esca, meaning food. It was applied by ancient peoples to a certain species of oak; somehow the name was transferred over the years to the horse chestnut.
The name hippocastanum is thought to refer to the horse chestnut’s ability to heal horses and cattle of respiratory illnesses. Another possibility may be that it is named for the small horseshoe-like markings that are present on the branches of the horse chestnut tree.
Horse chestnut trees grow in nearly any soil but seem to prefer a sandy loam. They grow very rapidly into tall straight trees that can reach heights of over 100 ft (approximately 30 m) tall, with widely spreading branches.
The bark is grayish-green or grayish-brown in color, and the tree limbs are thick and have corky, elongated, wart-like eruptions that appear from a distance like ribbing. The interior of horse chestnut bark is pinkish-brown, with fine lines running its length. It is odorless and its taste is very bitter and astringent.
The characteristic horseshoe markings found on the branches are actually the scars from where leaves previously grew. Horse chestnut wood is seldom if ever used for lumber due to its soft and spongy character.
Large leaf and flower buds are clearly visible even during winter months but are encased in a scaly, resinous protective covering that prevents damage from frost or damp. This thick sticky coating melts with the beginning of warm weather in spring, and flowers and leaves appear with remarkable rapidity, usually within three to four weeks.
The leaves are dark green, rough in texture, and large, with minutely serrated edges. Horse chestnut leaves can be nearly 1 ft (0.3 m) in length. They somewhat resemble a hand with five to nine leaf sections emerging from a palm-like base to form the finger-like projections.
European horse chestnuts produce clusters of white flowers with a pale scarlet tinge at the throat or yellow mottling. American horse chestnut flowers can be white, pale pink, or yellow, depending upon the species. All types of horse chestnut trees, with their graceful wide limbs and showy flowers, are grown for their ornamental beauty.
The fruit of the horse chestnut is a dark brown smooth-surfaced nut approximately 2 in (5 cm) in diameter. It has a polished appearance except for the rounded dull tan-colored scar on the side that was attached to the seed vessel. Horse chestnuts are encased in a light green spine-covered coating that divides into three parts and drops away prior to the nut dropping from the tree.
Horse chestnut nuts contain mostly carbohydrates which are generally indigestible until boiled. They also contain saponins, tannin, flavones, two glycosides, aesculin and fraxin, some crude protein, a fatty oil, ash and water.
Horse chestnuts native to North America are called buckeyes because of their large seeds which resembling the eye of a buck, or male deer.
American horse chestnuts are divided into four types:
- Ohio buckeye, or Aesculus glabra, is a medium-sized tree which grows from the southern United States to the prairies of western Canada. It is the state tree of Ohio, hence the state’s nickname of the Buckeye State.
- Yellow buckeye, Aesculus octandra, or Aesculus flava, is a tree which grows to heights of 40 ft (12 m) or more. It is fairly common across the central portion of the United States. Its leaves are somewhat smoother than those of other horse chestnuts.
- Red buckeye, or Aesculus pavia, is a shrub or small tree that generally is found in the southern United States. In early summer it develops brilliantly scarlet flowers in large clusters, and has dense foliage. The tree species of red buckeye grows to heights of between 15–20 ft (5–7 m) tall.
- California buckeye, or Aesculus californica, is a horse chestnut tree found all along the Pacific coast.
Horse chestnuts have been used as fodder for feeding farm animals, and some Native American peoples have included them in their diet. However, the outer covering of the horse chestnut nut is toxic, and the nut itself has to be boiled prior to being eaten safely. Its wood, which is too soft for furniture-making or construction, is used in building crates and other packing cases.
Both the bark and the fruit from horse chestnut trees are used medicinally to strengthen and tone the circulatory system, especially the venous system. It is used both internally and externally to treat varicose veins, phlebitis, and hemorrhoids.
Horse chestnut preparations are particularly effective in treating varicose ulcers. Due to its ability to improve circulation, it is also helpful for the relief of leg cramps. Its bark also has narcotic and fever-reducing properties.
A compound known as aescin, which is present in the horse chestnut fruit, is now often added to external creams and preparations used for the treatment of varicose veins, varicose ulcers, bruises, and sports injuries.
Horse chestnut preparations using the seed, bark, twigs, and leaves are all utilized in traditional Chinese medicine. Chinese herbalists consider horse chestnut to be a part of treatment not only for circulatory problems, but use it as an astringent, as a diuretic, for reduction of edema or swelling, to reduce inflammation, as an expectorant in respiratory problems, and to fight viruses.
Horse chestnut bark is removed in the spring in strips 4 or 5 in (10–13 cm) long, about 1 in (2.5 cm) thick and broad. The fruit of the horse chestnut is gathered in the autumn, when they fall from the tree. Both the bark and the fruit are dried in sunlight or with artificial heat, and are either kept whole or ground to a powder for storage.
A decoction made of 1 or 2 tsp of the dried, pulverized bark or fruit left to simmer for 15 minutes in 1 cup of water can be either taken internally three times a day or used externally as a lotion. Horse chestnut preparations are also available as tinctures, extracts, capsules, and external ointments and lotions.
The outer husks of the horse chestnut fruit are poisonous. There are also reported cases of poisoning from eating raw horse chestnuts.
There have been reported cases of gastrointestinal irritation, nausea, and vomiting from taking large doses of horse chestnut. There are also rare reports of rash and itching, and even rarer cases of kidney problems.