The Burr Oak is a large, deciduous tree with a very wide, open crown. Usually wider than tall, the tree can exceed 100 feet in height and width. The massive trunk supports heavy, horizontal limbs and rough, deep-ridged bark. Leaves up to 9 inches long with a central midrib from which branch veins lead into rounded lobes. The acorns are distinguished by very deep fringed cups and are the largest of all native oaks. The common name of the tree describes the cup of the acorn, which slightly resembles the spiny bur of a chestnut. The acorns are large, up to 1.5 inches broad with roughly half of the acorn enclosed in the cup. The acorn cup has coarse scales and a fringed margin.