|Bur oak leaves and acorn|
Michx. 1801 not Endl. 1848
|Generalized natural range|
Quercus macrocarpa, the bur oak, sometimes spelled burr oak, is a species of oak in the white oak section Quercus sect. Quercus, native to North America in the eastern and central United States and eastern and central Canada. This plant is also called mossycup oak and mossycup white oak.
Quercus macrocarpa is widespread in the Atlantic coastal plain from New Brunswick to North Carolina, west as far as Alberta, eastern Montana, Wyoming, and northeastern New Mexico. The vast majority of the populations are found in the eastern Great Plains, the Mississippi/Missouri/Ohio Valley, and the Great Lakes region.
Quercus macrocarpa is a large deciduous tree growing up to 100 ft (30 m), rarely 130 ft (40 m), in height, and is one of the most massive oaks with a trunk diameter of up to 10 ft (3 m); reports of taller trees occur, but have not been verified. It is one of the slowest-growing oaks, with a growth rate of 1 ft (30 cm) per year when young. However, other sources state that a burr oak tree that is planted in the ground grows up to 3 ft (91 cm) per year. A 20-year-old tree will be about 20 ft (6 m) tall if grown in full sun. Naturally occurring saplings in forests will typically be older. It commonly lives to be 200 to 300 years old, and may live up to 400 years. The bark is a medium gray and somewhat rugged.
The leaves are 3–6 in (7–15 cm) long and 2–5 in (5–13 cm) broad, variable in shape, with a lobed margin. Most often, the basal 60% is narrower and deeply lobed, while the apical 40% is wider and has shallow lobes or large teeth. The flowers are greenish-yellow catkins, produced in the spring. The acorns are very large, 0.75–2 in (2–5 cm) long and 0.75-1.5 in (2–4 cm) broad, having a large cup that wraps much of the way around the nut, with large overlapping scales and often a fringe at the edge of the cup.
The acorns are the largest of any North American oak (thus the Latin species name macrocarpa—large fruit), and are an important wildlife food; American black bears sometimes tear off branches to get them. However, heavy nut crops are borne only every few years. In this evolutionary strategy, known as masting, the large seed crop every few years overwhelms the ability of seed predators to eat the acorns, thus ensuring the survival of some seeds. Other wildlife, such as deer and porcupine, eat the leaves, twigs and bark. Cattle are heavy browsers in some areas. The bur oak is the only known foodplant of Bucculatrix recognita caterpillars.
Bur oak typically grows in the open, away from forest canopy. For this reason, it is an important tree on the eastern prairies, often found near waterways in otherwise more forested areas, where there is a break in the canopy. It is a fire-resistant tree, and possesses significant drought resistance by virtue of a long taproot. New trees, after two to three years of growth, may have a 1–2 m deep taproot. The West Virginia state champion bur oak has a trunk diameter of almost 3 m (9 feet).
The bur oak is among the most fire-tolerant tree species. One of its most common habitats, especially in Midwestern United States, is the oak savanna, where fires often occurred in early spring or late fall, especially in hill country.
Quercus macrocarpa is cultivated by plant nurseries for use in gardens, in parks, and on urban sidewalks. Bur oak makes an outstanding ornamental tree. Among the white oaks, it is one of the most tolerant of urban conditions, and is one of the fastest-growing of the group. It has been planted in many climates, ranging northwards to Anchorage, Alaska, and as far south as Mission, Texas. It withstands chinook conditions in Calgary, Alberta.
The name sometimes is spelled "burr oak", as for example in Burr Oak State Park in Ohio, the city of Burr Oak, Kansas, the village of Burr Oak, Michigan, and in the title Burr Oaks by poet Richard Eberhart.
- Bur oak blight, a fungal disease affecting bur oak trees.
- Kenny, L.; Wenzell, K. (2015). "Quercus macrocarpa". IUCN Red List of Threatened Species. IUCN. 2015: e.T33991A2839807. doi:10.2305/IUCN.UK.2015-4.RLTS.T33991A2839807.en. Retrieved 12 November 2016.
- The Plant List, Quercus macrocarpa Michx.
- "Quercus macrocarpa". County-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). 2013.
- http://www.ldeo.columbia.edu/~adk/oldlisteast/Spp/QUMAC.html Eastern OLDLIST
- Nixon, Kevin C. "Quercus macrocarpa". Flora of North America (FNA). Missouri Botanical Garden. 3 – via eFloras.org.
- "Quercus macrocarpa Michx. bur oak". Natural Resources Conservation Service. US Department of Agriculture. Retrieved August 8, 2013.
- "Richard Eberhart". Poetry Foundation. Bibliography: Poetry Foundation. Retrieved 2 February 2017.
Burr Oaks, Oxford University Press (New York, NY), 1947.
- CRW: Flag of Ann Arbor (c. 1970 – present)