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Tree of Merit: Overcup Oak (Quercus lyrata) by Cene Ketcham, Extension Arborist, Casey Trees O vercup oak (Quercus lyrata)—sometimes known as swamp post oak or water white oak—is a tough shade tree in the white oak group. Though it can sometimes be dif- ficult to source, its popularity for use along streets and in the landscape has been increasing—a testament to the growing interest in this species. At first glance, overcup oak is some- times confused with swamp white oak (Q. bicolor), post oak (Q. stellata), or with its close relative, bur oak (Q. macrocarpa). Although it shares some attributes with these species, closer inspection reveals a tree with a character all its own. In the swamp forests it inhabits in the wild, it can reach heights of 100 feet (30 m) or more (the current champion, in Isle of Wight, Virginia, is 109 feet/33 m feet tall with a crown spread of 103 feet/31 m). However, in an urban setting it is more typ- ically around 40 feet/12 m high and wide. The mature crown is rounded and quite consistent between individuals; in youth, it is more pyramidal-oval. It requires little pruning to develop good structure. Branches are generally well-spaced and resis- tant to breakage, with lower branches upswept, reducing the need for crown raising along streets and sidewalks. Its fall color is not particularly showy and its light gray, scaly bark (similar to white oak or swamp white oak), while interest- ing, is not especially remarkable. It is instead distinguished by its utterly unique acorns and highly variable leaves. As you can expect from its common name, the nut of the rounded, 3/4 to 1-inch (1.9 to 2.5 cm) acorn is almost completely enclosed within the warty cap, leaving only a small opening at the bot- tom. This adaptation allows the acorns to float on the water in its swampy habitat. The specific epithet, lyrata, refers to the alleged lyre-shape of the leaves, though I have a tough time seeing the resem- blance. Leaves are alternate, 4 to 8 inches (10 to 20 cm) long, with 3 to 5 pairs of blunt lobes. The lower two sets of lobes are smaller and separated from the upper by wide, square sinuses; the upper lobes are generally triangular. Leaves have a somewhat leathery texture, with deep green color above, pubescent and white to light green below. Twigs are gray-brown with gray or white lenticels and brown, ovoid (left) Foliage of Q. lyra- ta. Photo by Rebekah D. Wallace, University of Georgia, Bugwood.org (right) The winter habit of a young Q. lyrata. This specimen will require only minor structural pruning. Note the upward sweep of the branches (compare to downward sweep of the lower branches of pin oak/ Q.palustris). Photo by Cene Ketcham (far right top) The twig of overcup oak is gray-brown with small, ovoid buds. End buds are clustered in the usual oak fashion. Photo by Cene Ketcham (far right middle) The acorn of Quercus lyrata is almost completely enclosed in its cap. Photo by Cene Ketcham (far right bottom) The underside of the overcup oak acorn. Photo by Chris Evans, University of Illinois, Bugwood.org 38