The conker tree
The horse chestnut (Aesculus hippocastanum) is a large tree native to the Balkans and planted widely in parks and streets. Despite its name it is not related to the edible sweet chestnut. On the right are its key features, magnified.
Hand-shaped leaves
Each leaf has 5–7 large leaflets spreading like fingers from one long stalk, with the middle one biggest. Leaves and twigs grow in opposite pairs, and the crown is a dense, dark green dome.
Spring candles
In April and May the tree carries upright white 'candles' of flowers. Each flower has a yellow spot that guides bees to the nectar and turns pink once the flower has been pollinated.
Autumn conkers
By September each pollinated flower has become a green husk with short, stout spines. Inside is a glossy brown conker with a pale scar. Sweet chestnut husks, by contrast, are covered in dense, fine needles.
How it spreads
Conkers are heavy, so they mostly drop below the tree, bounce and roll. Squirrels and other animals carry some away and bury them as food stores, and the ones they forget can grow into new trees.
From seed to tree
In spring a buried conker sends a root down and a shoot up, while its seed leaves stay underground to feed it. Saplings grow fast, start flowering after roughly a decade or more, and can reach 25–35 m and live about 300 years.
Winter clues
With the leaves gone, look for big, shiny, sticky red-brown buds and horseshoe-shaped leaf scars dotted with 'nail holes' on stout twigs. Those scars are one reason it is called a horse chestnut.