A picturesque oak with stout, rugged branches, the bur oak grows to 80 feet tall or more and has a broad, spreading, rounded crown. Leaves are dark, lustrous green above and gray or whitish and hairy below. Fall color is a dull yellow-brown. Male and female flowers are produced in separate catkins on the current year's growth. Male catkins are yellowish, slender and hanging.
Female catkins occur in reddish clusters on a short stalk.
The broadly ovoid acorns are 0.8 to 2 inches long with the cup covering one-half or more of the nut. A distinctive fringe of long, soft bristles protrudes from the rim of the cup and the tip of the nut has a short beak. The reddish-brown, imbricate buds are conical to broadly ovate and are densely covered with fine, gray hairs. Bark is thick, dark gray-brown and separated into irregular, scaly ridges. It is the most widely distributed native oak in Iowa and the most abundant tree in the forests of the western and north central parts of the state.