- For the South African Thoroughbred racehorse see: Horse Chestnut (horse).
The genus Aesculus, the buckeyes and horse-chestnuts, comprises 13-19 species of deciduous trees and shrubs native to the temperate northern hemisphere, with 6 species native to North America and 7-13 species native to Eurasia; there are also several hybrids. They have traditionally been treated in the ditypic family Hippocastanaceae along with Billia[1], but recent phyloegentic analysis of morphological[2] and molecular data[3] has led to this family, along with the Aceraceae (Maples and Dipteronia), being included in the soapberry family (Sapindaceae).
The North American species are known as buckeyes and the Eurasian species as horse-chestnuts. Some are also called white chestnut or red chestnut (as in some of the Bach flower remedies. In Britain, they are sometimes called conker trees because of their link with the game of conkers, played with the nuts, also called conkers.
Etymology
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". Linnaeus named the genus Aesculus after the Roman name for an edible acorn. The use of the term "horse" refers to their strength or inedibility, and does not here refer to their fitness as fodder for horses, except in folk etymology. The name buckeye derives from the resemblance of the seed to the brown eye of a buck (male deer), and horse-chestnut from the external resemblance of the seed to a chestnut, but being inedible. The buckeye blooms in summer and the horse-chestnut in late spring.
Description
Horse chestnut flowers in Ayrshire, Scotland.
Aesculus are woody plants from 4 to 36m 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). Flowers showy, insect-pollinated, with four or five petals fused into a lobed corolla tube, arranged in a panicle inflorescence. Flowering starts after 80–110 growing degree days. The fruit is a rich glossy brown to blackish-brown capsule 2–5 cm diameter, usually globose with 1-3 seeds (often erroneously called nuts) per capsule, more than 2 results in seeds being flat on one side; the point of attachment of the seed in the capsule (hilum) shows as a large circular whitish scar. The capsule epidermis has "spines" (botanically: prickles) in some species, other capsules are warty or smooth, capsule splits into three sections to release the seeds.[4][5][6]
Cultivation
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. 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. × 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. Common horse-chestnut is also used as a food plant by the sycamore, another species of moth.
Another disease in parts of North West Europe and North America is bleeding canker[7][8].
Uses
The nuts contain high concentrations of a saponin-class toxin called aesculin, which is toxic to many animals including humans because it causes hemolysis (destruction of red blood cells). The saponin can be eliminated by leaching the pulverized nuts in multiple changes of boiling water, to yield a wholesome starchy porridge once important to some Native American peoples. Some animals, notably deer and squirrels, are resistant to the toxins and can eat the nuts directly. An interesting side-note is that aesculin is a natural pH indicator which, when extracted turns from colorless to fluorescent blue under UV light in an acidic pH range.
California buckeye Aesculus californica is known to cause poisoning of honeybees from toxic nectar (native bee species not being affected). Other buckeye species are thought to have the same effect, but the toxins are diluted because the trees are not usually abundant enough in any one area.citation needed
The wood is very pale whitish-brown, fairly soft and little-used. Uses include cheap furniture, boxes and firewood.citation needed
In Britain and Ireland the game of conkers remains a common childhood pastime.
In some cultures, the buckeye tree is thought to bring good luck.
The Mexican buckeye is related to Aesculus, but is in a separate genus, Ungnadia.
Extractives of the seeds have been shown to be useful for the treatment of chronic venous insufficiency. [9]
References
- ^ Hardin, JW. 1957. A revision of the American Hippocastanaceae I. Brittonia 9:145-171.
- ^ Judd, WS, RW Sanders, MJ Donoghue. 1994. Angiosperm family pairs. Harvard Papers in Botany. 1:1-51.
- ^ MG Harrington, KJ Edwards, SA Johnson, MW Chase. 2005. Phylogenetic inference in Sapindaceae sensu lato using plastid matK and rbcL DNA sequences. Systematic Botany. 30:366–382
- ^ Hardin, JW. 1957. A revision of the American Hippocastanaceae I. Brittonia 9:145-171
- ^ Hardin, JW. 1957. A revision of the American Hippocastanaceae II. Brittonia 9:173-195
- ^ Hardin, JW. 1960. A revision of the American Hippocastanaceae V, Species of the Old World. Brittonia 12:26-38
- ^ UK Forestry Commission page on bleeding canker
- ^ Dutch page on bleeding canker (in English)
- ^ Horse Chestnut - Aesculus hippocastanum [NCCAM Herbs at a Glance]
Gallery
Chinese horse-chestnut (Aesculus chinensis) young leaves in spring ...
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... and fully grown, in summer
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Aesculus hippocastanum bud opening in spring
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Red horse-chestnut (Aesculus x carnea)
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External links
- Germplasm Resources Information Network: Aesculus
- Forest, F., Drouin, J. N., Charest, R., Brouillet, L., & Bruneau A. (2001). A morphological phylogenetic analysis of Aesculus L. and Billia Peyr. (Sapindaceae). Canad. J. Botany 79 (2): 154-169. Abstract.
- Aesculus glabra (Ohio buckeye) King's American Dispensatory
- Ohio Buckeye Trivia Cards tell about the buckeye, buckeye tree, buckeye history, buckeye folklore and more.
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