The postcard shows a horse chestnut in blossom near Le Thoronet, France.
Aesculus hippocastanum is a large deciduous tree, commonly known as horse chestnut or conker tree.
The common name "horse chestnut" is reported as having originated from the erroneous belief that the tree was a kind of chestnut (though in fact only distantly related), together with the observation that eating the fruit cured horses of chest complaints despite this plant being poisonous to horses.
The nuts, especially those that are young and fresh, are slightly poisonous. Although not dangerous to touch, they cause sickness when eaten. When consumed by horses, they can cause tremors and lack of coordination. Some mammals, notably deer, are able to break down the toxins and eat them safely.
In Britain and Ireland, the nuts are used for the popular children's game "conkers."
Cultivation for its spectacular spring flowers is successful in a wide range of temperate climatic conditions provided summers are not too hot.