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.