Aesculus - Buckeyes and Horse-chestnuts
Aesculus hippocastanum
Scientific classification
Kingdom: Plantae Division: Magnoliophyta Class: Magnoliopsida Order: Sapindales Family: Sapindaceae Genus: Aesculus
Species
Aesculus arguta: Texas Buckeye Aesculus californica: California Buckeye Aesculus chinensis: Chinese Horse-chestnut Aesculus flava (A. octandra): Yellow Buckeye Aesculus glabra: Ohio Buckeye Aesculus hippocastanum: Common Horse-chestnut Aesculus indica: Indian Horse-chestnut Aesculus neglecta: Dwarf Buckeye Aesculus parviflora: Bottlebrush Buckeye Aesculus pavia: Red Buckeye Aesculus sylvatica: Painted Buckeye Aesculus turbinata: Japanese Horse-chestnut Aesculus wilsonii: Wilson's Horse-chestnut

The genus Aesculus comprises about 20-25 species of deciduous trees and shrubs native to the temperate northern hemisphere, with 7-10 species native to North America and 13-15 species native in Eurasia; there are also several natural hybrids. They have traditionally been treated in their own monogeneric family Hippocastanaceae, but genetic evidence shows that this family, along with the maples (Aceraceae), are better included in the soapberry family (Sapindaceae), as the differences between the three groups are small and of doubtful significance.

The North American species are known as Buckeyes and the Eurasian species as Horse-chestnuts. The name Horse-chestnut, hyphenated here to avoid confusion with the true chestnuts (Castanea, Fagaceae), is also often given as 'Horse Chestnut' or 'Horsechestnut'. One species very popular in cultivation, the Common Horse-chestnut Aesculus hippocastanum is also often known as just 'Horse-chestnut'. The name buckeye derives from the resemblance of the seed to the brown eye of a buck (male deer), and horse-chestnut from the superficial resemblance of the seed to a chestnut, but being inedible ("only fit for horses" - though the seeds are also poisonous for horses).

Aesculus are woody plants from 4 to 35 m 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); and showy insect-pollinated flowers, with a single four- or five-lobed petal (actually four or five petals fused at the base). Flowering starts after 80-110 growing degree days. The fruit is a rich glossy brown to blackish-brown nut 2-5 cm diameter, usually globose with one nut in a green or brown husk, but sometimes two nuts together in one husk, in which case the nuts are flat on one side; the point of attachment of the nut in the husk shows as a large circular whitish scar. The husk has scattered soft spines in some species, spineless in others, and splits into three sections to release the nut.

Common Horse-chestnut tree

The most familiar member of the genus worldwide is the Common Horse-chestnut Aesculus hippocastanum, native to a small area of the Balkans in southeast Europe, but widely cultivated throughout the temperate world for its spectacular spring flowers (see photo, below). The Yellow Buckeye Aesculus flava (syn. A. octandra) is also a valuable ornamental tree with yellow flowers, but is less widely planted. Among the smaller species, the Bottlebrush Buckeye Aesculus parviflora also makes a very interesting and unusual flowering shrub. Several other members of the genus are used as ornamentals, and several horticultural hybrids have also been developed, most notably the Red Horse-chestnut A. x carnea, a hybrid between A. hippocastanum and A. pavia.

They are generally fairly problem-free, though a recently discovered leaf-mining moth Cameraria ohridella is currently causing major problems in much of Europe, causing premature leaf fall which looks very unattractive. The symptoms (brown blotches on the leaves) can be confused with damage caused by the leaf fungus Guignardia aesculi, which is also very common but usually less serious.

A selection of fresh conkers from a Horse-chestnut. They are not true nuts, but rather capsules.

Uses.The nuts are poisonous, but some Native American tribes leached the pulverized nuts to make them edible. Crushed buckeye nuts have also been used, thrown into lakes by poachers, to kill fish for easy capture. Some animals, notably deer, are resistant to the toxins and can eat the nuts.

California Buckeyes Aesculus californica are known to cause poisoning of honeybees from toxic nectar (other locally native bee species not being affected). Other buckeye species are thought to have the same effect, but the toxins are diluted because the trees not usually abundant enough in any one area. In Britain, the nuts of Aesculus hippocastanum are used for the popular children's game conkers.

Aesculus hippocastanum flowers

The wood is very pale whitish-brown, fairly soft and little-used. Uses include cheap furniture, boxes and firewood. However, in Great Britain during the two world wars horse-chestnuts were processed for their starch content to manufacture acetone which was necessary in the production of cordite in armaments.

The Ohio Buckeye Aesculus glabra is the state tree of Ohio and an original term of endearment for the pioneers on the Ohio frontier, with specific association with William Henry Harrison. Subsequently, the use of the term for the Ohio State University sports teams made the term a widely known title for any graduate, or indeed, any Ohioan. Ironically, the world-record Ohio Buckeye tree is located in Kentucky, not Ohio, and as a consequence, there has for some time been a reward offered for anyone who discovers an Ohio Buckeye in Ohio large enough to become the new champion. Of small but interesting note is the Buckeye confection, which is made by encasing a dollop of peanut butter with milk chocolate. These can be found throughout Ohio, especially as a treat during Christmas time.

Historical uses

A Horse-chestnut tree in winter

Horse-chestnut seeds were used in France and Switzerland to whitening hemp, flax, silk and wool. They contain a soapy juice, fit for washing of linens and stuffs, for milling of caps and stockings, etc., and for fulling of cloth. For this, 20 horse-chestnut seeds were sufficient for six litres of water. They were peeled, then rasped or dried, and ground in a malt or other mill. The water must be soft, either rain or river water, for hard well water will not do. The nuts are then steeped in cold water, which soon becomes frothy, as with soap, and then turns white as milk. It must be stirred well at first, and then, after standing to settle, strained or poured off clear. Linen washed in this liquor, and afterwards rinsed in clear running water, takes on an agreeable light sky-blue colour. It takes spots out of both linen and woollen, and never damages or injures the cloth.

Poultry will eat horse-chestnut flour, if it is steeped in hot water, and mixed with an equal quantity of pollard. The nuts also are eat by some cows, and without harming their milk; they are reputed to be excellent for horses whose wind is injured.

California Buckeye (Aesculus californica) - leaves

External links

• Gutenberg Project (historical uses) (http://www.gutenberg.org/dirs/1/1/3/6/11369/11369.txt)
• Section Bach Flower information
  • Chestnut Bud (http://www.bachcentre.com/centre/38/chestbud.htm) Bach Flower Remedy
  • Chestnut, Red (http://www.bachcentre.com/centre/38/redchest.htm) Bach Flower Remedy
  • Chestnut, White (http://www.bachcentre.com/centre/38/whiteche.htm) Bach Flower Remedy

• Section Eclectic herbal information
  • Aesculus glabra (Ohio Buckeye) (http://www.ibiblio.org/herbmed/eclectic/kings/aesculus.html) King's American Dispensatory @ Henriette's Herbal
  • Aesculus hippocastanum (Horse Chestnut) (http://www.ibiblio.org/herbmed/eclectic/kings/aesculus-hipp.html) King's American Dispensatory @ Henriette's Herbal
  • Horse Chestnut (http://www.botanical.com/botanical/mgmh/c/chehor58.html) Mrs. Grieve's "A Modern Herbal" @ Botanical.com

• Section Herbal information
  • Horse Chestnut (http://www.mcp.edu/herbal/horsechestnut/horsechestnut.pdf) (pdf) Longwood Herbal Task Force
  • Horse Chestnut (http://www.mskcc.org/mskcc/html/11571.cfm?RecordID=437&tab=HC) Memorial Sloan-Kettering Cancer Centre
  • Horse Chestnut (http://www.healthy.net/library/books/hoffman/materiamedica/horsechest.htm) Herbalist David Hoffmann @ Health World

• Section Homeopathic information
  • Aesculus hippocastanum (aesc-hip.) (http://www.homeoint.org/books3/kentmm/aesc-hip.htm) "Kent's Lectures on Homeopathic Materia Medica" by Dr Robert Séror
  • Aesculus hippocastanum (http://www.homeoint.org/books5/allenprimer/aesc-h.htm) "A Primer of Materia Medica for practitioners of Homœopathy" by Timothy Allen