Aesculus hippocastanum

As of March 2023[update], Plants of the World Online considered it to be native to the Balkans (Albania, Bulgaria, Greece and former Yugoslavia), but also to Turkey and Turkmenistan.

[15] A 2017 assessment for the IUCN Red List restricted the native distribution to the Balkan area: Albania, Bulgaria, mainland Greece and North Macedonia.

Bulgaria's relict horse chestnut forests are critically endangered at the national level and protected as part of the Dervisha Managed Nature Reserve.

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,[19] the Faroe Islands,[20] Reykjavík, Iceland and Harstad, Norway.

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.

[24] Aesculus hippocastanum is affected by the leaf-mining moth Cameraria ohridella, whose larvae feed on horse chestnut leaves.

To further protect the cellars from the summer heat, they would plant horse chestnut trees, which have spreading, dense canopies but shallow roots which would not intrude on the caverns.

[30] There is risk of acute kidney injury, "when patients, who had undergone cardiac surgery were given high doses of horse chestnut extract i.v.

[31] Raw horse chestnut seed, leaf, bark and flower are toxic due to the presence of aesculin and should not be ingested.

A fine specimen of the horse-chestnut was outside the window of the "secret annex" in the centre of Amsterdam, which Anne Frank mentioned in her diary and which survived until August 2010, when a heavy wind blew it over.

After a long quarantine in Indianapolis, each tree was shipped off to a new home at a notable museum or institution in the United States, such as the 9/11 Memorial Park, Little Rock Central High School, and two Holocaust Centers.

Inflorescence
Floral diagram of A. hippocastanum . The light green structure denotes nectary. Floral formula : ↘ K5 C2:2 A5+2 G (3).
A selection of fresh conkers
Remainders of horse chestnut flower spikes found on the ground below. The chestnuts themselves have separated with their burs from the small branches shown.
Remainders of two horse chestnut flower spikes – one 27 cm long – with two chestnuts found on the ground under the tree. The chestnuts themselves have separated with their burs from the small branches shown.
Horse-chestnut leaf miner ( Cameraria ohridella ) tree damage in Parma, Italy