| Aesculus | |
|---|---|
 | |
| Aesculus hippocastanum, the European horse chestnut | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Sapindales |
| Family: | Sapindaceae |
| Subfamily: | Hippocastanoideae |
| Genus: | Aesculus L. |
| Type species | |
| Aesculus hippocastanum | |
| Species | |
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ThegenusAesculus (/ˈɛskjʊləs/[1] or/ˈaɪskjʊləs/), with notable species includingbuckeye andhorse chestnut, comprises 13–19 species offlowering plants in the familySapindaceae. They aretrees andshrubsnative to thetemperate Northern Hemisphere, with six species native to North America and seven to 13 species native to Eurasia. Severalhybrids occur.Aesculus exhibits a classicalArcto-Tertiary distribution.[a]
Mexican buckeye seedpods resemble theAesculus seedpods, but belong to a different genus.
Carl Linnaeus named the genusAesculus after the Roman name for an edible acorn. Common names for these trees include "buckeye" and "horse chestnut", though they are not in the same order as the true chestnuts,Castanea in theFagales. Some are also calledwhite chestnut orred chestnut. In Britain, they are sometimes calledconker trees because of their link to the game ofconkers, played with the seeds, which are also called conkers.
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Aesculus species have stout shoots with resinous, often sticky, buds, with opposite, palmately divided leaves, often very large—to 65 cm (26 in) across in the Japanese horse chestnut,A. turbinata. Species are deciduous or evergreen. Flowers are showy, insect- or bird-pollinated, with four or fivepetals fused into a lobedcorolla tube, arranged in a panicle inflorescence. Flowering starts after 80–110growing degree days. The fruit matures to acapsule 2–5 cm (1–2 in) diameter, usually globose, containing one to three seeds (often erroneously called anut) per capsule. Capsules containing more than one seed result in flatness on one side of the seeds. 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, while other capsules are warty or smooth. At maturity, the capsule splits into three sections to release the seeds.[3][4][5]
Aesculus seeds were traditionally eaten, afterleaching, by theJōmon people of Japan over about four millennia, until 300 AD.[6][7][8]
All parts of the buckeye or horse chestnut tree are moderately toxic, including the nut-like seeds.[9][10] The toxin affects the gastrointestinal system, causing gastrointestinal disturbances. TheUSDA notes that the toxicity is due tosaponinaescin andglucosideaesculin, withalkaloids possibly contributing.[11]
Native Americans used to crush the seeds and the resulting mash was thrown into still or sluggish waterbodies to stun or kill fish.[11][12] They then boiled and drained (leached) the fish at least three times to dilute the toxin's effects.[13] New shoots from the seeds also have been known to kill grazing cattle.[14]
The genus was considered to be in the ditypic familyHippocastanaceae along withBillia,[15] but phylogenetic analyses of morphological[16] and molecular data[17] have more recently caused this family, along with theAceraceae (maples andDipteronia), to be included in the soapberry family (Sapindaceae).
The species ofAesculus include:
| Image | Scientific name | Common name | Distribution |
|---|---|---|---|
 | Aesculus assamica | northeast India (Sikkim) eastward to southern China (Guangxi) and northern Vietnam | |
 | Aesculus hippocastanum | horse chestnut | southeastern Europe |
 | Aesculus indica | Indian horse chestnut | southern Asia |
 | Aesculus chinensis | Chinese horse chestnut | eastern Asia |
 | Aesculus californica | California buckeye | western North America |
 | Aesculus flava (A. octandra) | yellow buckeye | eastern North America |
 | Aesculus glabra | Ohio buckeye | eastern North America |
 | Aesculus parviflora | bottlebrush buckeye | eastern North America |
 | Aesculus parryi | Parry's buckeye | western North America, endemic to Baja California del Norte |
_Hippocastanaceae_(1657458344).jpg) | Aesculus pavia | red buckeye | eastern North America |
 | Aesculus sylvatica | painted buckeye | eastern North America |
 | Aesculus turbinata | Japanese horse chestnut | Japan |
The most familiar member of the genus worldwide is the common horse chestnut,Aesculus hippocastanum. 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 is the bottlebrush buckeye,Aesculus parviflora, a 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 chestnutAesculus ×carnea, a hybrid betweenA. hippocastanum andA. pavia.
Interpretations of the tree leaves can be seen in architectural details in theReims Cathedral.[citation needed]
The horse chestnut was not native to Britain and was only introduced from Europe in 1650 (on the estates of bothDawyck House andStobo Castle).[18]
The leaf of Aesculus was the official symbol ofKyiv on itscoat of arms used from 1969 to 1995.[19] It remains an official symbol of Kyiv to this day.[19]
In the1840 U.S. presidential campaign, candidateWilliam Henry Harrison called himself the "log cabin and hard cider candidate", portraying himself sitting in a log cabin made of buckeye logs and drinking hard cider, causing Ohio to become known as "the Buckeye State".[20]
InGeneva, Switzerland, anofficial chestnut tree is used to indicate the beginning of theSpring; every year since 1818, the tree is observed by the secretary of theGrand Council of Geneva (the local parliament), and the opening of the first leaf is recorded and announced publicly. Over the years, four different horse chestnut trees have been used for these recordings.
In North America, several native American tribes, particularly in the western and central United States, such asMiwok, Pomo, Yokut, Maidu, historically used Buckeye trees (Aesculus spp.) like California Buckeye to harvest fish by utilizing thesaponins, which had been extracted by the plant's seeds. These tribes used crushed Buckeye nuts to release saponins into streams or shallow water, where the compounds would stun or kill the fish, allowing for easier capture.
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