Exploring the Horse Chestnut Tree in BC and the UK

A flowering horse chestnut tree beside a trail near my home

The horse chestnut tree was part of my life in the UK and still is in British Columbia. I think it’s a lovely tree. The leaves and flowers are attractive, and the prickly fruit and shiny brown seeds (the conkers) are interesting to examine. The seeds have been used in a traditional game known as “conkers” for a long time. The seeds aren’t edible and are actually poisonous. This fact should be kept in mind. Conkers can be admired and handled, but they mustn’t be eaten.

The tree’s scientific name is Aesculus hippocastanum. It’s native to Europe and belongs to the family Sapindaceae, or the soapberry family.  Though the word “chestnut” is part of its common name, it isn’t closely related to the trees bearing edible chestnuts. It’s appreciated for its beauty and its fruits. Multiple horse chestnut trees in a row can create an attractive avenue of plants when the leaves, flowers, or fruits are present. The tree is deciduous. I always look forward to its awakening in the spring.

I took this photo at an animatronic dinosaur display. The Triceratops and the Tyrannosaurus rex were placed on a lawn by some horse chestnut trees.

Mature horse chestnut trees are tall. Some reach a hundred feet in height. The large leaves make the plant hard to miss. At the right time of the year, the flowers and the conkers also attract the attention of passers by. The leaves are palmately compound, which means that the multiple leaflets emerge from a single point. The leaflets are toothed and have a pointed tip. They have very noticeable veins.

The flowers of the horse chestnut are mostly white, but their base is decorated with yellow or pink blotches. The flowers are arranged in erect spikes. The spikes are sometimes referred to as candles. I can understand why. They do resemble lights when the flowers are open. It’s interesting to see the “lights” in the relatively dark background of my first photo.

A semi-wild horse chestnut tree beside a garden near my home

The fruit is large and prickly. It generally contains one seed but sometimes contains two or three. The immature fruit is green but turns yellow as it matures. The mature seeds, or conkers, are brown with a white area at one end. They contain some interesting chemicals. Two of these chemicals have similar names. It’s important that they aren’t confused because one is poisonous and the other isn’t.

Aesculin (or esculin) is toxic. The harmful effects of the chemical depend on the amount that’s eaten and are variable. It’s not a substance that should be experimented with. It’s toxic for dogs as well as humans. Aescin (or escin) is not considered to be toxic when present in appropriate quantities. Though some sources use the name to represent a single chemical in the saponin group, others use the name to refer to a group of saponins in a conker. Saponins produce a foam when mixed with water. Horse chestnut chemicals are sometimes use medicinally, but they must be prescribed and formulated by medical experts to ensure safety.

Conkers and a shell that I discovered; one theory for the horse chestnut’s name is the shape of the white mark on the seed sometimes resembles a horseshoe

I don’t remember ever playing a game of conkers, but it’s still popular in some areas and has been since at least the nineteenth century. The player creates a hole that travels through the conker. A piece of string is then passed through the hole. A knot is tied at once end so that the string doesn’t fall out of the hole. Two players meet while carrying their seeds. One person swings their conker at the other person’s. The goal is to break the opponent’s conker. The scoring method is somewhat complicated, but the general idea is that the more opponents that a particular conker breaks, the higher its score.

The World Conker Championship takes place on the second Sunday in October in a Northamptonshire village known as Southwick. It’s an event that I’d like to attend one day. Northamptonshire is a county located in the East Midlands area of England. The conker competition raises money for the visually impaired.

The tail of an animatronic T. rex and a horse chestnut tree with unripe fruit; the tip of the tail swung from side to side during each animation sequence and gently moved some of the leaves

Unfortunately, the leaf miner moth (Cameraria ohridella) and bleeding canker disease are creating problems for some horse chestnut trees in the UK. The caterpillar of the leaf miner moth makes the leaves of the tree turn brown in the fall and causes the tree to appear unsightly. Most of the leaves’ photosynthesis has been performed by the time that the caterpillar attacks, however, so the insect doesn’t cause significant harm to the tree.

Bleeding canker disease is a more serious problem for the horse chestnut. It’s caused by a bacterium named Pseudomonas syringae. The bacterium creates a canker (an infected and visibly damaged area) in the bark of the tree. The infection may progress deeper into the tree and even into the wood. Here it may interfere with the plant’s ability to transport food and water. The injured area releases a red liquid, which makes the tree look as though it’s bleeding. The tree may or may not die, depending upon the seriousness of the infection and the plant’s ability to resist the bacterium.

It can kill affected trees, although some do recover from infection, and some appear to be resistant to it.

Forest Research, UK Government (with reference to bleeding canker disease)
Young horse chestnut leaves in spring (Photo by Jarmila at Pixabay)

I’ve been fond of horse chestnut trees and their conkers since my childhood in Britain. There are two trees very close to my home in British Columbia that I can observe. Both appear to be healthy. I enjoy watching their life cycle as the year progresses as well as taking photographs of them. I’m still delighted to discover conkers, just as I was when I was a child. The horse chestnut is one of my favourite trees.