Horse chestnut

Horse chestnut
Aesculus hippocastanum

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Horse chestnut belongs to the genus Aesculus and is a member of the Horse chestnut family (Hippocastanaceae).

Horse chestnut (Aesculus hippocastanum) is a deciduous tree growing to over 35m and flowering late April to May.

Lifespan: Horse chestnut can live over 300 years.

Characteristics

Bark is grey-brown, separating into scaly plates with age. Twigs are hairless, stout and curve upwards at the ends. Buds are oval, dark red, shiny and sticky in spring.

Leaves are long-stalked and palmate, divided into 5–7 leaflets of 8–20cm long. Each leaflet is pointed at the tip, tapered at the base, toothed and hairless. Leaf stalks leave a scar on the twig which resembles an inverted horse shoe with nail holes.

Flowers are grouped into large ‘panicles’. Individual flowers have four to five fringed petals, which are white with a pink flush at the base, stamens protrude and arch downwards.

Horse chestnut trees are hermaphrodite. This means that they have ‘perfect’ flowers with both sexes represented in one flower. However, horse chestnuts often have some male-only flowers.

Fruits are 6cm, globular, green with prickly spines. Within are one to three seeds of deep, rich, glossy red-brown, 3–4cm across known as ‘conkers’.

Horse chestnut is insect pollinated.

Horse chestnut tree

Horse chestnut leaf

Horse chestnut fruit

Distribution

The horse chestnut is native to the Balkan peninsula and was introduced to Britain in the 1600s.

Horse chestnut is naturalised in the UK. Widely planted and self-sown, it is commonly found in parks, gardens, village greens and residential streets, and is often planted in avenues.

Horse chestnut is not commonly found in woodland but it can form a small element of the canopy in National Vegetation Classification W12 Fagus sylvatica – Mercurialis perennis (Beech – Dogs mercury) woodland.

Horse chestnut can be an important landscape element in wood pasture and parkland habitat where very large and veteran specimens survive.

 

Human value

Horse chestnut timber is a pale creamy white to light brown with a smooth, soft, fine texture. The timber is light in weight due to its rapid growth and is not very strong as a result. For this reason it is not used commercially. However, the softness of the wood makes it excellent for carving.

An extract obtained from the seeds and bark contains an active compound aescin (saponin) which is used in herbal remedies for its anti-inflammatory and astringent properties.

The horse chestnut is most valued as an amenity tree for its abundant, fragrant, candle-like flowers.

Generations of children have enjoyed using the large seeds to play the competitive game of ‘conkers’.

Horse chestnut flower
Horse chestnut leaves

Wildlife value

The nectar-rich flowers of the horse chestnut are important for bees and other nectar-loving insects, and the Triangle moth has been found to feed on its leaves. The seeds are reportedly eaten by deer and other mammals.

Horse chestnut comes into flower early in the year and has become an important species for the UK Spring Index. The Index is calculated from the dates of four different annual biological events: the first flowering of hawthorn; the first flowering of horse chestnut; the first recorded flight of an orange-tip butterfly; and the first sighting of a swallow.

The Index provides contextual information that shows how changes in climatic variables, particularly temperature, can lead to changes in the timing of biological events, and assists in monitoring climate change.

Management

Horse chestnut is a fast-growing species best suited to moist, well-drained soils. It is able to tolerate a wide range of conditions including dry sandy soils, wet clays and chalk but it is not tolerant of salt spray

Seeds ripen in September and can be collected and planted straight away. Seeds are highly perishable and may not survive drying and freezing.

Horse chestnut has been found to be susceptible to Phytophthora.

Horse chestnut trees can be affected by bleeding canker which can seriously damage tree health and lead to death. A few cases of this may have been caused by Phytophthora; however, the majority of infections are caused by the bacteria Pseudomonas syringae pathovar aesculi.

The horse chestnut leaf miner (Cameraria ohridella) can infest trees and damage the foliage causing it to turn brown and fall early – as shown, right. There is no evidence at present to suggest that infestation causes a decline in tree health, because most of the damage occurs very late in the growing season.

Horse chestnuts may also suffer from Guignardia leaf blotch caused by the fungus Guignardia aesculi, and from horse chestnut scale – apparent as circular white spots on trunks or branches caused by the insect Pulvinaria regalis.

Leaf miner

Illustrations © Reader’s Digest Association, Inc.
Photographs © Debbie Cotton