Often simply called the 'conker tree', for the fruit used in the traditional game of conkers. Horse Chestnut is among our most flamboyant trees, with candelabra-like upright spring flower clusters; the genus epithet contains the Ancient Greek word for horse. Introduced 1616, it grows in recreation grounds, parks, large gardens and occasionally woodland edges.
Native to the Albania, Bulgaria, northern Balkan peninsula, Greece, Turkmenistan and Turkey. Very widespread across north-west Europe, absent only from higher elevations, and from exposed western coasts in Scotland and Ireland.
Monoecious, with both bisexual and unisexual flowers (hermaphrodite at the base, male towards the tip). Insect-pollinated, especially by bees and hoverflies, guided by a 'traffic light' system where petal bases are yellow before pollination and turn pink-red afterwards. Only 2-5 flowers at the base set fruit (conkers), the heaviest seeds of any European tree, dispersed by gravity.
Large (35m) with a broad-domed (20m) canopy of heavy sweeping branches. Bark grey, becoming rough and scaly. Twigs have horseshoe-shaped leaf scars with visible vascular dots; buds opposite, red-brown, sticky-resinous. Leaves large, palmate compound with 5-7 sessile ovate leaflets (to 30x12cm), the terminal largest, dark green above, brown-haired vein axils below, irregularly toothed. Flowers (20-50) in upright panicles (30cm), white with basal spots turning from yellow to pink, May-June. Fruit a spiky dehiscent capsule with 2(-3) glossy brown conkers with a pale hilum. Indian Horse Chestnut differs: stalked leaflets, pink flowers a month later, smooth husks, darker seeds.
Prefers deep, well-drained soils, tolerating pollution and exposure, though its heavy branches are wind-vulnerable in summer when dense foliage acts as a sail. Seeds are poisonous to humans, pets and horses (causing colic), containing aesculin and other toxins. Leaves damaged by Horse Chestnut Leaf Miner can be raked and burned or composted to reduce local reinfection.
A good source of nectar for insects, especially bumblebees and solitary bees. Holes created by broken limbs provide nesting sites for birds like the Jackdaw (Coloeus monedula).
Horse Chestnut Leaf Miner is a micro-moth whose larvae mine the leaves, turning them prematurely brown in summer; mainly an aesthetic problem but it may affect long-term growth. More serious is bleeding canker, caused by the bacterium Pseudomonas syringae pv. aesculi, which oozes dark sticky liquid and, as it spreads, can girdle and kill branches or the whole tree.
Ornamental, although the leaf miner has severely limited this potential. Its timber is soft and weak, but was traditionally used for toys and cheap utensils.
