Bur, or mossy cup, oaks are massive, spreading trees with conspicuous, large dark branches and rounded leaf lobes. The acorns have a distinctive, large cap with "burs", hence the name.
The bur oak is native to the eastern US, extending into south central US. 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. Due to its thick bark, the bur oak was able to withstand prairie fires and could grow on the edges of the plains, making it a forest fringe species. The bur oak is a considerably important timber tree in the US. Although it makes an excellent shade tree, the bur oak is seldom planted in urban areas, as young trees are difficult to transplant, slow to grow and the mature tree has an extensive root system.
The leaves of Quercus macrocarpa are simple, alternate and lobed. It can be distinguished from the other oaks by the blunt lobes, most leaves with a single pair of deep sinuses, corky ridges on the branches, and the fringe along the margin of the acorns.
This is a relatively slow-growing tree but long-lived (300 years or more).
Bur Oak ranges from Manitoba to Texas, east through Tennessee and West Virginia to Maine and Quebec (absent from the Atlantic coastal states). It is common and distinctive in southern Wisconsin, and is found to a lesser extent throughout the state, although it is apparently absent in Door County, or nearly so. Habitat is most often drier sites, and it is well known for tolerance to fire, but it is sometimes also found on moist sites.
The bur oak acorn is a food source for larger seed-eating birds and squirrels when other food sources are scarce in the winter.