Bur Oak, Mossycup Oak, or Burr Oak

(Fagaceae - Beech Family)

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• Form
  • large shade tree
  • maturing at about 70' tall by 60' wide under urban conditions, but much taller and wider in its native habitat
  • upright oval growth habit in youth, becoming rounded, spreading, and massive with age
  • slow to medium growth rate

• Culture
  • full sun to partial sun (partial shade tolerant in youth)
  • performs best in full sun in moist or dry, neutral or alkaline pH soils, but is very urban tolerant (including tolerance to severe drought, pollution, high pH soils, poor soils, sandy soils, and compacted clay soils) and also adapts to acidic soils
  • propagated by seeds
  • Beech Family, with no serious diseases or pests
  • moderately available in ball and burlap form
  • member of the White Oak group; some of these members may hybridize freely in the wild, resulting in a blending of such traits as leaf shape and acorn caps
  • Burr Oak is very sensitive to being transplanted in Autumn, and care should be taken to amend the soil, fertilize, water thoroughly, mulch adequately, and avoid Winter salt spray, to enhance survival chances during the first Winter, if transplanting cannot be delayed until Spring

• Foliage
  • dark green, alternate, strongly obovate, and deeply sinuate in the middle of the leaf blade, with about three pairs of lobes on the narrow lower one-third of the leaf and five to seven pairs of subtle lobes on the wide upper one-third of the leaf
  • the large dark green leaf blade (about 10" long and 5" wide) is thick and leathery, having a lighter-colored underside that yields a more subtle bicolor in the breeze as compared to some other White Oak Group members, and is supported by a short yet stout petiole
  • overall leaf shape resembles a base fiddle or violin, but the detailed leaf structure (depth of sinuses and prominence/number of lobes) is quite variable, even on the same twig
  • fall color is yellow-brown to chartreuse and usually poor

• Flowers
  • yellow-brown pendulous male catkins are obvious and prominent in late April, but are ornamentally insignificant, as are the very small pistillate flowers

• Fruits
  • a huge (1.5" long) oval acorn with a thick cap that is fringed at the lower end, covering almost the entire nut (hence the common names of Burr Oak or Mossycup Oak), borne singly on a stout short peduncle, and maturing in a single season

• Twigs
  • brown-gray, very stout and bold-textured, and often slightly corky after the first year

• Trunk
  • gray, very deeply furrowed and grooved with age, with vertical, flattened, narrow ridges (up to 4" thick on very old trees) that primarily run parallel to each other, forming a very distinctive appearance and contributing to the very bold texture of mature trees

• ID Summary
  • Burr Oak has several unique traits among large shade trees: fiddle-shaped foliage that is thick and large, bark on lower trunks that has thick, vertical flattened ridges with very deep furrows, large fringed acorns, and stout semi-corky twigs; in addition, the tree often stands alone in fields in the wild, displaying its bold texture of a massive trunk and huge spreading limbs from a distance, and being very drought tolerant due to its very deep taproot system

• Function
  • shade tree for large lawns, golf courses, parks, open fields, or naturalized areas, including areas that are very dry in the Summer
  • valuable timber tree, with its wood prized for beams, boards, railroad ties, furniture, and floors

• Texture
  • very bold texture in foliage and when bare
  • thick density in foliage but open density when bare

• Assets
  • very urban tolerant (including extreme drought tolerance and alkaline soil tolerance)
  • very bold texture (in both Summer and Winter)
  • nuts attract wildlife (large birds, deer, and especially squirrels)
  • very cold hardy

• Liabilities
  • difficult to successfully transplant due to its coarse root system, including a deep tap root
  • relatively slow growth rate for a shade tree
  • fall color is usually poor
  • significant fruit and leaf litter with age

• Habitat
  • zones 2 to 8
  • native to the Eastern United States, but also naturalized to the Great Plains of the United States (where its thick bark aids in survival during occasional prairie grass fires)

• Alternates
  • trees of very bold texture (Ailanthus altissima, Carya ovata, Ginkgo biloba, Gymnocladus dioicus, Juglans nigra, Quercus alba, Quercus prinus, etc.)
  • trees for very dry sites (Celtis occidentalis, Fraxinus pennsylvanica, Gleditsia triacanthos, Populus deltoides, Quercus marilandica, Quercus prinus, Quercus stellata, etc.)
  • shade trees capable of massive dimensions (Acer saccharum, Ailanthus altissima, Carya ovata, Catalpa speciosa, Fraxinus americana, Ginkgo biloba, Liriodendron tulipifera, Populus deltoides, Quercus alba, Quercus rubra, Ulmus americana, etc.)
  • wildlife attraction hardwood trees (members of the genera Fagus, Carpinus, Carya, Juglans, Nyssa, Quercus, etc.)

• Variants
  • straight species is the available form

NOTES

• Translation
  • Quercus is the Latin name for Oak.
  • macrocarpa translates as "large carpel", referring to the very large acorn.

• Purpose
  • Bur Oak is the most bold-textured of the largest Oaks, having a picturesque appearance in the landscape either in Summer fiddle-shaped foliage or Winter semi-corky stem and straight-ridged trunk outline, having the largest acorn of any Oak, and is also one of the most drought-tolerant large trees, with a deep tap root system that penetrates to the depths of the lowered water table during the dry periods of Summer.

• Summary
  • Quercus macrocarpa is known as a massive shade tree that can tolerate prolonged drought, native to the Eastern United States but planted extensively in the Great Plains during the 1800's as a firestorm-resistant and drought-tolerant shade tree.