19Horse chestnut
Aesculus hippocastanum
The 19th stop on the tour is a tree located at the back entrance of the Max Delbrück Communication Center. It is a horse chestnut, botanical name Aesculus hippocastanum, from the horse chestnut family or Hippocastanaceae. The name Aesculus was given to it by the botanist Carl Linneaus. He took the name from a species of oak called aesculus in ancient times. The tree received its name horse chestnut because of its seeds, the chestnuts, and their use as horse feed and remedy for a type of cough in horses.
The horse chestnut can grow up to 30 meters high and live for about 300 years. The trunk can grow to two meters in diameter and bears a smooth and brown, sometimes slightly reddish bark. The branches bear hanging twigs, forming a dense and very broad crown. The leaves of the horse chestnut are pinnate: each leaf consists of several leaflets that appear to be separated from each other. Underneath, the leaflets have felt-like veins. The flowering period lasts from about April to June. They undergo an unusual color change after pollination. The white flowers have a yellow spot when unfertilized; it turns red after pollination. In September, the capsule fruits ripen. They are green, spiny and usually bear one seed, the chestnut, and in rare cases two or three.
The horse chestnut is native to Asia Minor and the Balkan Peninsula. The Ottomans discovered that it had healing properties in horses, and brought the horse chestnut to Central Europe. From the 16th century it became a popular tree for castle gardens and avenues. It is very frost hardy and prefers nutrient-rich and fresh to moist sandy and loamy soils. As a sun-loving tree with shallow roots, it does not like to stand in close proximity to other trees.
It has proven to have many uses as a medicinal plant. A variety of pharmacologically active substances can be extracted from the bark, seeds, flowers and leaves, mainly coumarins such as aescin, but also saponins and other substances. Horse chestnut extracts are used against inflammation and respiratory diseases in both animals and humans. Dried leaves are used against warts, insufficiency of veins, and hemorrhoids. Because β-escin is hemolytically active, extracts of chestnuts are used against chronic venous insufficiency, edema, for feelings of heaviness and tightness in the leg area, and for painful injuries such as sprains. The flowers are used as an astringent and tonic as well as for gout and rheumatism. The oil extracted from chestnuts can be eaten as an edible oil, but is mostly used as a base for soap and lubricants. Last but not least, chestnuts are used in animal feed and are popular among children for handicrafts.
The horse chestnut is an endangered species due to a prevalent strain of the horse chestnut leaf miner moth. It was chosen as the Tree of the Year 2005 in Germany. In addition, the horse chestnut was named medicinal plant of the year 2008.
Sidebar: The horse chestnut leaf miner moth
In Central Europe it is hard to find a horse chestnut tree whose leaves do not show brown spots in summer. The reason for this is the caterpillar form of the horse chestnut leaf miner moth (Cameraria ohridella). This small insect develops almost exclusively in the leaves of the horse chestnut. First discovered in 1984 in a narrowly defined area of Macedonia, it spread outward very rapidly across Central Europe. The reason is a lack of natural predators. Initially, it was feared that infestation would lead to the death of the trees. So far, this has not proven to be true, although the early and severe loss of leaves weakens the trees, as seen by the fact that the chestnuts of infested trees are significantly smaller.
