By Drew Chaney, Center for Urban Habitats
Oaks are among the most familiar of the tree species that make up Virginia’s forests. From their acorns to their (typically) lobed leaves, many of us can recognize an oak, even if we don’t know which of the 28 species found in Virginia it is.
Oaks native to eastern North America fall into two broad categories, white oaks and red oaks. White oaks are characterized by their leaves with rounded, smooth-tipped lobes and acorns that mature the autumn after flowering, while red oak leaves have lobes that are tipped with a short stiff bristle, as well as often being “sharper” in appearance. Some of our red oak species have leaves which are unlobed, these still display the bristle at the apex of the leaf. Red oak acorns mature in the autumn of the year after flowering.
The majority of species in Virginia belong to the red oak group, and these can pose an identification challenge due to the similarities between their bark and leaves. Fortunately, the experienced observer can learn to distinguish between them with practice.
This post will show you how to differentiate between the seven most commonly found members of the red oak group in the Central Virginia Piedmont.
The willow oak (Quercus phellos) is the most distinctive of the bunch, with its narrow, unlobed leaves.
The remaining six species discussed here are all ones that can be found easily by the casual observer in the Central Virginia Piedmont. A couple of other species of red oak do occur infrequently but are unlikely to be found without a dedicated search. A brief overview of these will be provided at the end of this post.
Northern Red Oak (Quercus rubra)
The Northern Red Oak’s leaves can be distinguished by their 7 to 9, shallow, triangular lobes. The leaves of Black Oak are similar, but typically have 5 main lobes and often a more irregular shape. The green, living foliage can further be distinguished by its smooth undersides (Black Oak is fuzzy below). Northern Red Oak bark is furrow and dark gray on mature trees, with lighter, smooth stripes in the center of each plate of bark. This feature is common in the Red Oak group but seems most pronounced in this species and Scarlet Oak.
Northern Red Oak is found across the entire state of Virginia. In the central Piedmont, it is most characteristic of oak-hickory forests and mesic slopes. It does not occur frequently in the driest of soils, nor in wetlands.
Black Oak (Quercus velutina)
Black Oak foliage typically displays 5 to 7 lobes. The shape of the leaf is quite variable. Black Oak leaves from the lower part of the tree are often large and very shallowly lobed, in order to maximize sunlight exposure. Upper leaves are more deeply lobed. The photograph above illustrates some of the variation. The differences between this species and the Northern Red Oak are described under the entry for that species. Black Oak also resembles the Blackjack Oak, which has leaves uniformly widest near the tip with three lobes. Black Oak bark is dark and furrowed.
Black Oak is common across the entire state of Virginia including the central Piedmont, and often occurs in drier soils than the similar Northern Red Oak. The two can occur together in oak-hickory forests, but Black Oak almost never ventures downslope into more mesic slopes and coves.
Blackjack Oak (Quercus marilandica)
The Blackjack Oak is one of the most distinctive of our oak species. Its foliage is widest near the tip of the leaf, and has three primary lobes, typically quite shallow. The leaf shape is variable, as seen in the photo above, and these shapes can be likened to those of a pear, fiddle or bird foot. The living foliage is thick and dark, lustrous green above, with some rusty hairs beneath. Blackjack Oak bark is very dark and rugged in appearance.
The Blackjack Oak is found across much of Virginia at low elevations, though it is rarely common. It is slow growing and well adapted to fire, and can be found in dry uplands, often with pines, and poorly drained clay hardpan soils which are alternately wet and dry at different periods of the year.
Southern Red Oak (Quercus falcata)
Southern Red Oak foliage is quite variable in its shape. The leaves typically display 3 to 5 lobes, and these can be shallow or deep, broad or slender. Often the lobes are slightly curved in shape, like the blade of a scythe or sickle. This is the origin of its specific name “falcata” (Latin for sickle-shaped). The most reliable character for identifying this species is the U or bell-shaped base of the leaf. The underside of the foliage is also covered in a dense tawny coat of hair when living. Its bark is similar to the other red oaks.
Southern Red Oak is common across the eastern two-thirds of the state, and can be found in a wide variety of dry to mesic forests, as well as various early-successional habitats.
Scarlet Oak (Quercus coccinea)
The Scarlet Oak can be distinguished from the similar Northern Red Oak by its much deeper lobes, and from the Black Oak by having foliage that is uniformly deeply lobed. Pin Oak is similar but has smaller foliage usually with fewer lobes and occurs in different habitats (see below). Living Scarlet Oak foliage differs even further from Black Oak by being smooth underneath (vs fuzzy). Scarlet Oak is named for its fall foliage, which is usually a stunning red. The bark is quite similar to that of Northern Red Oak.
Scarlet Oak is common across Virginia. In the central Piedmont it can be found in a wide variety of dry uplands, including oak-heath, pine-oak, and oak-hickory forests. Unlike Pin Oak, it never occurs in wetlands.
Pin Oak (Quercus palustris)
The Pin Oak is quite similar to the Scarlet Oak but has smaller foliage (7-12 cm long vs 7-20 cm for Scarlet), with 5 to 7 lobes (vs 5 to 11). Its bark is similar to Scarlet, but Pin Oak often displays lower branches that are angled downwards. These lower branches cling to the trunk even when dead and offer a useful clue for identification. Pin Oak rarely overlaps with Scarlet Oak in habitat.
Pin Oak is widely distributed in Virginia, but is most frequent in the northern part of the state. It can be found in floodplains, depression wetlands, and alternately wet and dry clay hardpan soils. It is also frequently planted as a street and shade tree due to its fast growth and tolerance of compacted soils.
Three other red oaks can be found occasionally in the area. Bear Oak (Quercus ilicifolia), Shumard Oak (Quercus shumardii), Shingle Oak (Quercus imbricaria). Bear Oak is a shrub found mainly in the Appalachians which occurs rarely in the Piedmont on rocky slopes and other shallow, dry soils. It has small, sharply lobed leaves easily distinguished from other red oaks by their silvery undersides. Shingle Oak is a widely distributed but uncommon oak of hardpans, upland depression wetlands, and other poorly drained soils. It has unlobed leaves similar to Willow Oak, but they are larger, wider and a darker, glossier green in color. Shumard Oak is a large, majestic species of bottomlands and slope forests with base-rich soils. It resembles a Scarlet Oak with larger, darker green foliage that often stays green into early winter, and shallower acorn cups.
References
- Flora of Virginia. Alan S. Weakley, J. Christopher Ludwig, and John F. Townsend.
- Nature’s Garden: A Guide to Identifying, Harvesting, and Preparing Edible Wild Plants. Samuel Thayer.
