Biological Flora of the British Isles: Aesculus hippocastanum

Abstract

Abstract This account presents information on all aspects of the biology of Aesculus hippocastanum L. (horse‐chestnut) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation. Aesculus hippocastanum is a large deciduous tree native to the Balkan Peninsula. Native populations are small (<10,000 trees total) and apparently in decline, but the tree has been widely planted in gardens and streets across Europe and other temperate areas from the 17th century onwards. It was voted the UK's favourite tree in a 2017 poll. As a British neophyte, it is occasionally naturalised in open wooded habitats. Horse‐chestnut is renowned for the beauty of its large (up to 30 cm long), upright panicles of white flowers, and for the large seeds (up to 42 g each) used in the formerly common children's game of “conkers.” More recently, the triterpene glycosides, extractable from various plant parts but especially the seeds, have been widely used in medicine. In much of Europe, horse‐chestnut is affected by chestnut bleeding canker (caused by Pseudomonas syringae pv. aesculi), the horse‐chestnut leaf miner Cameraria ohridella and the leaf blotch fungus Guignardia aesculi. The canker is likely to lead to death of <10% individuals, but seeds of plants infested with the leaf miner are 40%–50% smaller, which may affect long‐term establishment in non‐planted areas.