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.
Above: Pin Oak has a straight trunk, pyramidal shape, with pendulous lower branches, horizontal middle branches and upper branches that are ascending. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: Leaves on Pin Oak are more similar in shape than some of the other oak species but these 3 examples, all from the same tree, show a range of variation. The sinus of the larger lobes having a "U" shape and cut nearly to the mid-vein and the lower lobes tend to be slightly recurved when the base is truncate (1st photo) or obtuse shaped as seen here in the 2nd & 3rd photos. Both surfaces are smooth.
Below: The underside of the leaf is smooth except for tufts of brownish hair near the main veins.
Below: The male flowers are hanging catkins from the leaf buds of leaf axils of last years' growth. Just above them on the new growth twig (2nd photo) are the female flowers. The male catkin develops just as the leaves are unfolding. (3rd photo).
Below: 1st photo - The female flowers are greenish-red on a spur twig; twig and bracts with fine hair. 2nd photo - Maturing acorns of Pin Oak have a thin saucer shaped cup.
Below: Mature acorns. Photo ©Steve Hurst, USDA-NRCS Plants Database
Below 1st photo - Young acorns display the tightly appressed scales on the shallow cup. Only the green acorn expands with age, not the cup. 2nd photo - Bark on old trunks fissured into short, broad but shallow, scaly ridges. 3rd photo - Twigs, initially green, become reddish-brown by autumn when the new buds have formed.
Below: Leaf color on oaks is quite variable depending on the season and weather, but Pin Oak can display gorgeous reds at times before turning a glossy brown.
(1) Ascent of the Oaks, Hipp, Manos, Cavender-Bares, SA, Aug 2020.
Pin Oak is not found in the wild in Minnesota but has been shown to grow here in the correct environment. Minnesota is just beyond its northwestern range. It is found in the southern counties of Wisconsin and the SE corner of Iowa, then south and east of there in the midsection of the U.S. to the east coast, excepting upper New England, although it was introduced into Maine. It has been reported in Ontario in Canada.
There are six species of Oak generally found in parts of Minnesota that are not considered hybrids or rarities that have not been collected in the last 100 years. These are: White Oak, Q. alba; Swamp White Oak, Q. bicolor; Northern Pin Oak, Q. ellipsoidalis; Bur Oak, Q. macrocarpa; Northern Red Oak, Q. rubra. and Black Oak, Q. velutina. Chinkapin Oak (Chestnut Oak, or Yellow Oak), Q. muhlenbergii was native but is historical only now, last collected in 1899; Scarlet Oak, Quercus coccinea, can also grow here as can Pin Oak, Quercus palustris, but neither are native.
Historical - Eloise Butler: It is said that Pin Oak was one of her favorite trees. This is an interesting point, as the species is not native to Minnesota, but introduced. It was introduced to Maine where she grew up. At the memorial ceremony for Eloise on May 5, 1933, a Pin Oak was planted near the position of the large boulder that today holds her memorial plaque. The tree was not long-lived as that area is a bit too shaded for the species. Several times another has been planted there but none survive.
Uses: Pin Oak wood is hard and strong, but tends to warp so it is used for fuel, pulp and rail-road ties.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"