Aesculus hippocastanum

Aesculus hippocastanum, the horse chestnut, is a species of flowering plant in the soapberry and lychee family Sapindaceae. It is a large deciduous, synoecious (hermaphroditic-flowered) tree. It is also called horse-chestnut, European horsechestnut, buckeye, and conker tree. It is sometimes called Spanish chestnut. This name is typically used for Castanea sativa.

Description

Aesculus hippocastanum is a large tree, growing to about 39 metres (128 ft) tall^:371 with a domed crown of stout branches; on old trees the outer branches are often pendulous with curled-up tips. The leaves are opposite and palmately compound, with 5-7 leaflets; each leaflet is 13-30 cm (5-12 in) long, making the whole leaf up to 60 cm (24 in) across, with a 7-20 cm (3-8 in) petiole. The leaf scars left on twigs after the leaves have fallen have a distinctive horseshoe shape, complete with seven “nails”. The flowers are usually white with a yellow to pink blotch at the base of the petals; they are produced in spring in erect panicles 10-30 cm (4-12 in) tall with about 20-50 flowers on each panicle. Its pollens are not poisonous for honey bees. Usually only 1-5 fruits develop on each panicle; the shell is a green, spiky capsule containing one (rarely two or three) nut-like seeds called conkers or horse-chestnuts. Each conker is

2-4 cm (3/4–1+1/2 in) in diameter, glossy nut-brown with a whitish scar at the base.

Uses

It is widely cultivated in streets and parks throughout the temperate world, and has been particularly successful in places like Ireland, Great Britain and New Zealand, where they are commonly found in parks, streets and avenues. Cultivation for its spectacular spring flowers is successful in a wide range of temperate climatic conditions provided summers are not too hot, with trees being grown as far north as Edmonton, Alberta, Canada, the Faroe Islands, Reykjavik, Iceland and Harstad, Norway.

The seeds are used in Britain and Ireland for conkers, a popular game for children. During World War I, there was an appeal to everyone to collect the seeds and give them to the government. Conkers were used to provide starch for fermentation with the Clostridium Acetobutylicum method. This was used by Chaim Weizmann in order to make acetone, which was used as a solvent to produce cordite. Although Weizmann could use any starch source, the government requested conkers in order to avoid starvation due to depleting food resources. But conkers were found to be a poor source, and the factory only produced acetone for three months; however, they were collected again in the Second World War for the same reason.

Some seeds, particularly those that are fresh and young, can be slightly poisonous because they contain alkaloid saponins as well as glucosides. They are not hazardous to touch but can cause sickness if they are eaten by horses.

The horse-chestnut is a favourite subject for bonsai.

Though the seeds are said to repel spiders there is little evidence to support these claims. The presence of saponin may repel insects but it is not clear whether this is effective on spiders.

Aesculus hippocastanum is affected by the leaf-mining moth Cameraria ohridella, whose larvae feed on horse chestnut leaves. Although the moth was first described in North Macedonia, where it was discovered in 1984, it took 18 years for it to reach Britain.

In Germany, they are commonly planted in beer gardens, particularly in Bavaria. Before the invention of mechanical refrigeration, brewers used to build cellars for lagering. They would also plant chestnut trees to protect their cellars from the summer heat. These trees have dense, spreading canopies, but no roots that would intrude into the caverns. This practice evolved into modern beer gardens.

Medical uses

The seed extract standardized to around 20 percent aescin (escin) is used for its venotonic effect, vascular protection, anti-inflammatory and free radical scavenging properties. Primary indication is chronic venous insufficiency. A Cochrane Review suggested that horse chestnut seed extract may be an efficacious and safe short-term treatment for chronic venous insufficiency, but definitive randomized controlled trials had not been conducted to confirm the efficacy.

Safety

Two preparations are considered: whole horse chestnut extract (whole HCE) and purified b-aescin. Whole HCE was used for both oral and intravenous routes since 2001. The rate of adverse effects is low; in a large German study, 0.6%, consisting mainly of gastrointestinal symptoms.^{[medical citation needed]} Dizziness, headache and itching have been reported. Rare cases of anaphylactic reactions in the context of whole HCE are a serious safety concern.

Another risk is acute kidney injury. “When patients who had undergone heart surgery were given high doses i.v. of horse chestnut extract, they ran the risk of developing acute kidney damage. Postoperative oedema. It was dose dependent, as there was no evidence of kidney dysfunction at 340 mg/kg. Mild kidney impairment was detected at 360 mg/kg. Acute kidney injury was observed at 510 mg/kg. This almost certainly took place in a context of whole HCE.

To evaluate the effects of aescin upon kidney function, three clinical trials have been conducted. A total of 83 subjects were studied; 18 healthy volunteers given 10 or 20 mg iv. For 6 days, 40 patients with normal kidney function were given 10 mg IV. Two times daily (except for two children who were given 0.2 mg/kg), 12 patients suffering from cerebral oedema or normal kidney function received massive intravenous injections. dose on the day of surgery (49.2 +- 19.3 mg) and 15.4 +- 9.4 mg daily for the following 10 days and 13 patients with impaired kidney function due to glomerulonephritis or pyelonephritis, who were given 20-25 mg iv. Daily for six days. “In all studies renal function was monitored daily resorting to the usual tests of renal function: blood urea nitrogen (BUN), serum creatinine, creatinine clearance, urinalysis. Paraaminohippurate was also tested in a few cases. No signs of development of renal impairment in the patients with normal renal function or of worsening of renal function in the patients with renal impairment were recorded.” Aescin is very well tolerated in clinical settings.

Because of the presence esculin, raw horse chestnut seeds, leaves, bark, and flowers are toxic and should not to be eaten. FDA has classified horse chestnut seed as an unsafe herb. The glycoside and saponin constituents are considered toxic.