BIOLOGICAL FLORA OF THE BRITISH ISLES* No. 289 Biological Flora of the British Isles: Aesculus hippocastanum Peter A. Thomas1 | Omar Alhamd1,2 | Grzegorz Iszkuło3,4 | Monika Dering3,5 |Tarek A. Mukassabi6 1School of Life Sciences, Keele University, Staffordshire, UK 2College of Education for Pure Science, University of Mosul, Nineveh, Iraq 3Institute of Dendrology, Polish Academy of Sciences, Kórnik, Poland 4Faculty of Biological Sciences, University of Zielona Góra, Zielona Góra, Poland 5Poznań University of Life Sciences, Department of Forest Management, Poznań, Poland 6Department of Botany, University of Benghazi, Benghazi, Libya Correspondence Peter A. Thomas Email:
[email protected] 2 * Nomenclature of vascular plants follows Stace (2010) and, for non-British species, Flora Europaea. 3 Abstract 1. 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. 2. 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. 3. 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’.