Trees & Shrubs of the Eloise Butler Wildflower Garden

The Oaks of the genus Quercus account for more tree biomass than any other species in North America and Mexico (1). Pin Oak is a North American native (not to Minnesota) deciduous tree growing 50 to 80 feet high with a straight trunk, pyramidal shape, with pendulous lower branches, horizontal middle branches and upper branches that are ascending. Branches have numerous and persistent dead branchlets creating a spiny appearance and thus the name 'pin' oak. All these characteristics identify this species. The largest known Pin Oak in the country is in Cabell WV measuring 82 feet high, 66.5 foot crown spread, 208 inches in circumference and scoring 307 points.

The bark is reddish to grayish-brown, hard and smooth becoming with age, darker and fissured into short, broad but shallow, scaly ridges. The inner bark is pinkish.

Twigs are slender, reddish-brown in color, with multiple terminal buds that are relatively small, brown to reddish-brown, ovoid in shape, round in cross-section, normally without hair except sometimes a few fine hair at the apex. There are numerous light colored dotted lenticels on the twigs. Clusters of buds are located at the tips of the twigs.

The leaves are elliptic to oblong in outline with 5 to 7 deep lobes, cut nearly to the mid-vein in at least one place. The sinuses of the lobes are irregular to rounded with the larger lobes forming a "U" shape. The lobes are tipped with at least 10 and up to 30 pointed bristles (awns). The upper leaf surface is bright shiny green, the lower surface paler. Both surfaces are free of hair except for tufts of brownish hair on the underside at the veins. The base of the leaf is obtuse to truncate in shape and the base pair of lobes is frequently recurved when the base is truncate. Fall color is red to reddish brown.

Flowers: The tree is monoecious, that is with separate male and female flowers. Male flowers are a yellow-green, appearing in slender catkins, 2 to 4 inches long at the ends of the prior years growth. Each male flower has six stamens (can very from 2 to 12), which have long spreading white filaments when the flower fully opens. The female flowers are more reddish-green and appear as small slender spikes in the axils of new growth. They have 3 (to 6) carpels and styles that are slender and short and mounted on a short spur twig. There are no petals; both sexes have the sepals are fused together. Both appear with the leaves. Both the male catkins and the female flowers have hair.

Seed: The female flowers mature to a round, but slightly flattened acorn, 1/2 inch long, about 1/4 enclosed in a thin saucer-shaped cap with tightly pressed reddish-brown scales tapering abruptly to a stalked base. The nut is reddish-brown at maturity. The acorn matures in the following year -taking 16 to 18 months as do most species in the Quercus Sect. Lobatae - the Red Oak Group. The mature nut may have surface striations.

Habitat: Pin Oak is found in bottomlands that are moist to wet and uplands that have poorly drained soils. It is known to hybridize with Red Oak, Black Oak and Scarlet Oak. Unlike some of the oaks, Pin Oak has a shallow root system without a deep taproot and thus can be transplanted.

Names: The genus name, Quercus, is the Latin word for Oak. The species, palustris, means 'marsh loving' which is this species typical habitat. The author name for the plant classification from 1770, ‘Münchh’ is for Otto von Münchhausen (1716-1774) German botanist, correspondent of Linnaeus. He described several species of oak.

Comparisons: In our northern area Pin Oak resembles Northern Pin Oak, Black Oak , Northern Red Oak and most closely resembles Scarlet Oak. Note the differences in the acorns, especially the shallow cup of Pin Oak, bark and leaf. Also, the terminal buds are round in cross-section, not angled like the others. Another species that most closely resembles Pin Oak is the Texas Red Oak, Q. texana which is found only in the Texas-Louisiana-Mississippi area. It has the acorn cup deeply goblet- shaped, covering 1/3– 1/2 nut which is broadly ovoid to broadly ellipsoid, rarely less than 1/2 inch long. Check the Oak Leaf Comparison Sheet.