Distinguishing Dogwoods

Above: a flowering dogwood tree blossom featuring showy white bracts. Photo by Purdue Arboretum.

Many people in the Midwest know about and admire flowering dogwood trees and their distinctive spring flowers, which display conspicuous white or pink bracts (flower structures that resemble petals). Reportedly, George Washington and Thomas Jefferson were fans of this tree as well, planting them at their homes in Mount Vernon and Monticello, respectively. Did you know that we have nine native dogwood species in the Midwest?

I’m sourcing information from two books written by Purdue University experts, Native Trees of the Midwest and Shrubs and Woody Vines of Indiana and the Midwest.

All but one of our native dogwoods (Cornus spp.) have an opposite leaf arrangement, and the leaves look similar, with veins that form an arc that follows the leaf's shape toward the tip. This characteristic is known as arcuate venation. Fruit can vary among species, exhibiting hues of red, white, or blue. Fall leaf color usually ends in a deep red color. Although I won’t cover pith color (the center of the stem) in detail here, pith color of first- and second-year twigs is usually another good tool for identification. Most species have red or green twigs that add winter interest.

Homeowners may concentrate on the traditional flowering dogwood (C. florida) tree. It is a small tree, usually not exceeding 30-40 feet in height. It is moderately shade-tolerant and may struggle in full sun in home landscapes. In natural areas, it is typically found mixed with hardwoods and conifers in open woods and woods’ edges in rich, well-drained soils.

In addition to the flowering dogwood tree, other native dogwoods are considered shrubs.

Pagoda dogwood (C. alternifolia) is a small tree-sized shrub reaching heights of 18 to 20 feet. Its layered branching with upswept branch ends on older specimens resembles the roof of a Japanese pagoda. This shrub is also known as alternate-leaf dogwood; it is the only native dogwood with an alternate leaf arrangement. Fall leaf color features multiple hues and usually ends in deep burgundy. It is a beautiful and popular choice in home landscapes.

Bunchberry or dwarf cornel (C. canadensis) is the smallest of the native dogwoods. At a maximum height of 8 inches, it is classified as a sub-shrub. It is more common in northern states because it is unable to survive in soil temperatures greater than 65 degrees. Underground rhizomes allow large colonies of this plant to form.

Swamp dogwood (a.k.a. southern swamp dogwood, stiff dogwood; C. foemina or C. stricta) is found mainly in southern Indiana counties in poorly drained woodlands. It can grow to 9 feet in forest understories.

Rough leaf dogwood (C. drummondii or C. asperifolia) is one of our largest native shrubby dogwoods, growing to 12-15 feet or more. As the name suggests, leaves are rough with hairs on the underside. This shrub is easy to grow, but it needs room to grow. Suckers will give rise to new plants but can be controlled with mowing. First-year twigs are reddish-brown with flattened hairs, turning gray and hairless the second year.

Silky dogwood or pale dogwood (C. obliqua or C. amomum) has reddish twigs and a brown pith. The bark is reddish gray with vertical light brown shallow fissures, unique to this dogwood. In nature, this shrub is found along ponds, lakes, streams, and swamps, so it is usually associated with water. It is relatively easy to grow and is commonly found in nurseries.

Gray dogwood or northern swamp dogwood (C. racemosa) only gets about 4-5 feet tall. It frequently forms dense clonal communities that offer cover to wildlife. It can be found in nurseries that specialize in native plants. It is adaptable to wet or dry locations.

Round-leaf dogwood (C. rugosa) is a 5-6 feet tall shrub, more commonly found in the northern tier of Indiana counties. It has pinkish-green, purple, or yellow twigs that become rough with age. As the name suggests, its leaves are broadly ovate (rounder) than those of other shrub dogwoods and may resemble the leaves of flowering dogwood trees. Root suckering can produce small clumps that become small thickets over time.

Red-osier dogwood (a.k.a. red twig dogwood or American dogwood; C. sericea or C. stolonifera) is especially adaptable and the most widely available native shrub dogwood in midwestern nurseries. Its wine-red twigs (when young) are a landscape feature that stands out in winter. Bark on older specimens turns from red to greenish and eventually to grayish-brown. At up to 9 feet tall, it is one of the larger dogwoods, and it’s easy to grow and maintain. In natural areas, it is found in wet, boggy places and is a sun-loving shrub that will tolerate some shade.

You may also come across other non-native dogwoods available in nurseries, such as kousa dogwood (C. kousa), Tatarian dogwood (C. alba), or cornelian cherry dogwood (C. mas).

Identifying dogwoods (especially the shrubs) can be difficult, partly because all the leaves look similar. Finding a good field guide or identification book will help. Some plant identification apps may do a decent job but may need to be double-checked by a good reference book. Find additional information at the Purdue Arboretum, https://www.arboretum.purdue.edu/.