Swamp Dogwood (Cornus obliqua)

Description: This is a multistemmed shrub up to 12' tall. The coloration of branch bark varies with age and the local ecotype: it can be gray, brown, reddish brown, yellowish brown, or red. The bark of young branches is smooth and glabrous with scattered white lenticels (air pores), while the bark of older branches is more rough. The pith of young branches is brown. Young shoots are whitish green and terete; they are covered with short fine pubescence. Pairs of opposite leaves occur along young shoots and branches. The blades of these leaves are 2-5" long and ¾-2½ across; they are elliptic, lanceolate, or ovate with smooth margins. Each leaf blade has 3-5 pairs of curved lateral veins. The upper blade surface is yellowish green to medium green and glabrous. The lower blade surface is pale whitish green; it is either glabrous and glaucous or covered with minute dense hairs, especially along the major veins. The slender petioles are ½-1" long and either whitish green or reddish green; they are covered with short fine pubescence.

Flat-headed panicles of flowers occasionally develop among the upper branches and leaves, spanning about 2-3½" across. Individual flowers are about ¼" across, consisting of a short tubular calyx that is light green, 4 spreading white petals that are lanceolate, 4 stamens, and a pistil. The peduncles and pedicels of each panicle are light green to yellowish brown and either glabrous or covered with minute hairs. The blooming period occurs from late spring to mid-summer. The flowers have a sweet fragrance. Afterwards, the flowers are replaced by one-seeded globoid drupes about 1/3" (8 mm.) across; they become blue during the autumn and their interior is fleshy. The woody root system is shallow and spreading.

Cultivation: The preference is full or partial sun, wet to moist conditions, and either sandy or non-sandy soil that contains significant organic matter.

Range & Habitat: The native Swamp Dogwood is occasional throughout Illinois (see Distribution Map). Habitats include openings in moist woodlands, swamps, soggy thickets, wet prairies, edges of marshes, fens, and interdunal wetlands. While interdunal wetlands are always sandy, the remaining habitats can be either sandy or non-sandy. Occasionally this shrub is cultivated as a landscape plant, but it requires more moisture than most cultivated shrubs.

Faunal Associations: The nectar and pollen of the flowers attract many insects. These floral visitors include honeybees, bumblebees, Andrenid bees (Andrena spp.), Halictid bees (Halictus spp., Lasioglossum spp., etc.), various wasps, Syrphid flies, Tachinid flies, flesh flies (Sarcophagidae), blow flies (Calliphoridae), various butterflies, skippers, and other insects. Swamp Dogwood and other dogwood shrubs (Cornus spp.) are host plants of many insects that feed on their leaves, bore through their wood, suck on their plant juices, etc. The caterpillars of Celastrina argiolus (Spring/Summer Azure) feed on the flowers and buds of dogwood shrubs. Moth caterpillars that feed on these shrubs include Synanthedon scitula (Dogwood Borer), Bomolocha bijugalis (Dimorphic Bomolocha), Probole nyssaria (Dogwood Probole), Antispila cornifoliella (Heliozelid Moth sp.), and Caloptilia belfragella (Gracillariid Moth sp.); the caterpillars of the last two moths are leaf-miners. Other insect feeders include aphids (Aphis caliginosa, Aphis cornifoliae), leafhoppers (Erythroneura corni, Erythroneura ontari, Erythroneura rubrella), Clastoptera proteus (Dogwood Spittlebug), plant bugs (Plagiognathus cornicola, Lygocoris communis), Calligrapha philadelphica (Dogwood Leaf Beetle) and other leaf beetles, the larvae of Oberea tripunctata (Dogwood Twig Borer) and other long-horned beetles, the thrips Scirtothrips niveus, and the larvae of Macremphytus testaceus (Dogwood Sawfly). See the Insect Table for a more complete listing of these species.

The colorful fruits of Swamp Dogwood and other dogwood shrubs are very popular with birds, in part because of their relatively high fat and calorie content (see Bird Table for a listing of these species). Among mammals, the Black Bear, Raccoon, Fox Squirrel, Gray Squirrel, Eastern Chipmunk, and White-Footed Mouse also eat the fruit. White-Tailed Deer and Elk occasionally browse on the twigs and foliage, while the Beaver gnaws on the wood of shrubs that grow near bodies of water. There are also records of some turtles eating the fallen leaves, fruit, or seeds in wetland areas (Sotala & Kirkpatrick, 1973; Ernst et al., 1994); these species include Chelydra serpentina (Snapping Turtle), Emys blandingii (Blanding's Turtle), and Trachemys scripta (Slider).

Photographic Location: A sandy marsh at the Indiana Dunes National Lakeshore in NW Indiana.

Comments: Swamp Dogwood is one of the blue-fruited species of its genus. At one time, Swamp Dogwood was considered a subspecies of Silky Dogwood and it was referred to as Cornus amomum obliqua. However, it is now regarded as a distinct species. Silky Dogwood (Cornus amomum) differs from Swamp Dogwood by having rusty hairs underneath its leaves and its leaves are usually more broad in shape. Another blue-fruited species, Stiff Dogwood (Cornus foemina), differs by having leaf undersides that are hairless and green, rather than whitened; it also differs by having hairless leafy shoots and white pith in its twigs. Alternate-Leaved Dogwood (Cornus alternifolia) has drupes that are blue-black; it differs from Swamp Dogwood by having alternate leaves with slightly more pairs of lateral veins (4-6), a more tree-like habit of growth, and twigs with small white pith. Another commonly used name of Cornus obliqua is Pale Dogwood.