Horse chestnut (Aesculus hippocastanum) is a tree in which can be toxic to horses if parts are ingested. Horse chestnut trees are often found in urban and rural areas as ornamental and shade trees.

Horse chestnut trees are affected by pollution and as a result, in areas polluted by heavy metals its roots will become colonized by fungal endophytes. The tree can grow to heights exceeding 100 feet. The fruit produced is horse chestnuts--which are covered with a brown husk and hair-like spines which remain until the fruit ripens and splits open. The flowers bloom in late spring and appear as long green catkins which have a strong odor. In the fall the leaves turn bright yellow, gold and brown before dropping.