Horsechestnuts (Aesculus hippocastanum), also known as Conker Tree in England, are in the same genus as Buckeyes. Both are part of the same order as the Soapberry tree.
These trees are planted as street trees for ornamentation as well as shade. Both the National Audubon Society Field Guide to North American Trees and North American Trees (Preston and Braham, 2002) report them as “escaped.” The USDA maps show them as introduced in both the East and the Northwest. The tree originated in the Balkans but has been planted widely throughout Europe and other parts of the world. They may have been introduced in the United States as early as 1576.
Monumental trees lists the widest trunked tree in England, the tallest at over 120 feet in the Netherlands, and the oldest as a specimen in France, which might be as old as 500 years. The leaves are palmate, radiating out from a central point. This species isn’t listed in the National Forest Registry, but the Colorado Tree Coalition lists the largest and tallest tree in the state as one in Cedaredge. The largest Red Horsechestnut can be found in Denver.
The trees flower in May in what look like cones of white flowers. 
Sibley reports the interior yellow spots turn red when fertilized. The fertilized flowers produce what are known as conkers, or the “nut.” This is NOT the same as a sweet chestnut, and the outer casings look quite different. The two should not be confused as conkers are considered poisonous to humans, although they may be edible once boiled. Sweet chestnuts are encased in a spiny looking ball while the outer coating of a horse chestnut looks like bumpy leather. The interior “nuts” look similar but the edible version has a discernible and palpable point while the poisonous conkers are flat. Horsechestnuts are edible for many animals and are fed to horses and other livestock.
Apparently horsechestnuts are used in homeopathy. They are touted as useful for various circulatory problems such as venous insufficiency, phlebitis, and varicose veins when properly prepared. The leaves and bark may also be useful in a number of other conditions. Lupus is mentioned.
As they are not native to North America or The British Isles, there aren’t many myths associated with them. There is a game played in England called Conkers. This game is reported to have been a favorite of Roald Dahl. Currently, Britain’s trees are threatened by a combination of moths and disease. The loss of the trees may impact the World Conker Championship, which has been held in Northampton since 1965.
A notable characteristic of the Horsechestnut are the distinctive winter buds, which are large and sticky. 
Below is a short video about the Horse Chestnut in the United States.
The Red Horse Chestnut (Aesculus x carnea Briottii) is a cross between a Red Buckeye and the common Horsechestnut.
The flowers are red or pink and it is the most common large red-flowering tree in temperate zones (The Sibley Guide to Trees). The flowers are quite stunning. 
City Park’s Horsechestnut (Aesculus hippocastanum) (B115) can be found just west of the intersection of Jackson and Oak streets, across from 1312 W. Oak. This tree was planted in 1997 and had a diameter of about 3.5″
To locate the Red Horse Chestnut (Aesculus x crane Briotii) (A93), continue west on Oak Street to the first turn into the park. This street is a continuation of Roosevelt Avenue. The tree is one of the few deciduous trees in the NE triangle formed by Roosevelt and Sheldon Drive.
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