(Aesculus hippocastanum) Horse-chestnut

Aesculus hippocastanum is a species of flowering plant in the soapberry and lychee family Sapindaceae. It is a large deciduous, synoecious  (hermaphroditic-flowered) tree, commonly known as horse-chestnut or conker tree.

Description
Aesculus hippocastanum is a large tree, growing to about 39 metres (128 ft) tall 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 long, making the whole leaf up to 60 cm across, with a 7–20 cm 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 tall with about 20–50 flowers on each panicle. Usually only 1–5 fruit 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 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, the United Kingdom 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, Reykjavík, Iceland and Harstad, Norway.

In Britain and Ireland, the seeds are used for the popular children's game conkers. During the First World War, there was a campaign to ask for everyone (including children) to collect horse-chestnuts and donate them to the government. The conkers were used as a source of starch for fermentation using the Clostridium acetobutylicum method devised by Chaim Weizmann to produce acetone for use as a solvent for the production of cordite, which was then used in military armaments. Weizmann's process could use any source of starch, but the government chose to ask for conkers to avoid causing starvation by depleting food sources. But conkers were found to be a poor source, and the factory only produced acetone for three months; however, they were collected again in World War II for the same reason.

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.

Horse-chestnuts have been threatened by the leaf-mining moth Cameraria ohridella, whose larvae feed on horse chestnut leaves. The moth was described from Macedonia where the species was discovered in 1984 but took 18 years to reach Britain.

The flower is the symbol of the city of Kiev, capital of Ukraine. Although the horse-chestnut is sometimes known as the buckeye, this name is generally reserved for the New World members of the genus Aesculus.

In Germany, horse-chestnuts are often found in beer gardens, particularly in Bavaria. Prior to the advent of mechanical refrigeration, brewers would dig cellars for lagering. To further protect the cellars from the summer heat, they would plant chestnut trees, which have spreading, dense canopies but shallow roots which would not intrude on the caverns. The practice of serving beer at these sites evolved into the modern beer garden.

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 recent Cochrane Review found the evidence suggests that Horse Chestnut Seed Extract is an efficacious and safe short-term treatment for chronic venous insufficiency, but definitive randomized controlled trials are required to confirm the efficacy.

Aescin reduces fluid leaks to surrounding tissue by reducing both the number and size of membrane pores in the veins.
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https://en.wikipedia.org/wiki/Aesculus_hippocastanum