Description: This native perennial
plant is 1-4' tall, branching occasionally in the upper half. The light green
to reddish brown stems are usually glabrous; sometimes the central stem has
lines of hairs. The alternate leaves are up to 5" long and 2½" across
(excluding the petioles), becoming smaller as they ascend the stems; they are
medium to dark green. The lower leaves are cordate, while the upper leaves are
cordate-ovate or ovate; their margins are coarsely serrated. The upper surface
of each leaf is hairless, while the lower surface is either hairless or there
are hairs along the major veins. The narrow petiole of each leaf is about
one-half the length of the blade (up to 2½" long) and either unwinged or
slightly winged; it becomes shorter among the upper leaves. The upper stem
terminates in a panicle of flowerheads up to 1¼' long. This panicle is
longer than it is wide, and broader toward the bottom than the apex. When upper
side stems are present, much smaller panicles may be produced. Each small
flowerhead is about 1/2" across, consisting of 7-13 ray florets that surround a
similar number of disk florets. The slender ray florets are lavender, light
blue-violet, or white (rarely the latter). The tubular disk florets are
initially cream or pale yellow, becoming purple or reddish purple with
maturity. The base of each flowerhead is surrounded by slender floral bracts
that overlap each other in several series. These bracts are light green, except
for diamond-shaped patches of dark green toward their tips. The slender
peduncle of each flowerhead is short. Among the branches of the panicle, are
leafy bracts up to 1" long and smaller scale-like bracts. The blooming period
occurs from late summer into the fall and lasts about 1-2 months. Each disk
floret is replaced by an achene with a small tuft of white hairs; these achenes
are distributed by the wind. The root system is fibrous and it has creeping
rhizomes. This plant reproduces by reseeding itself and vegetatively through
its rhizomes.
Cultivation: The
preference is light shade or partial sun, moist to slightly dry conditions, and
soil that is loamy or rocky. Occasionally the foliage is affected by powdery
mildew and other kinds of disease during the fall. During hot dry weather, the
lower leaves may wilt and fall off. The size of this plant is variable
depending on the fertility of the soil and moisture conditions.
Range & Habitat: Blue Wood Aster occurs
occasionally in scattered counties across Illinois (see
Distribution
Map). It is more common in the northern half of the state than the lower
half. Habitats include moist to dry deciduous woodlands, woodland borders,
areas adjacent to woodland paths, thinly wooded bluffs, shaded areas along
streams, and rocky wooded slopes. Some disturbance is beneficial in heavily
wooded areas if it reduces excessive shade from the overhead canopy.
Faunal Associations: The nectar and pollen of the
flowerheads attract many kinds of insects, including long-tongued bees,
short-tongued bees, wasps, flies, butterflies, skippers, and beetles. Bees are
particularly important pollinators of the flowers. The caterpillars of the
butterfly Chlosyne nycteis (Silvery Checkerspot) feed on the foliage of
Aster spp. (Asters), as do the caterpillars of many moth species (see
Moth Table). Mammalian
herbivores, including rabbits, groundhogs, deer, and livestock, browse on the
foliage of Asters occasionally. The Wild Turkey eats the foliage and seeds of
Asters to a limited extent.
Photographic
Location: A rocky woodland in west-central Indiana. The
inflorescence is small because the photographed plant was growing in a dry
upland area of the woodland.
Comments: In Illinois, the Blue Wood Aster often
hybridizes with Aster sagittifolius (Arrow-Leaved Aster) and Aster
drummondii (Drummond's Aster), which can make identification of some
specimens very difficult. The Blue Wood Aster can be distinguished from both
Arrow-Leaved Aster and Drummond's Aster by its narrow petioles (see the lower
photograph); the petioles of the latter two species are conspicuously winged
with narrow green margins. Unlike Drummond's Aster, the Blue Wood Aster has
stems and leaf undersides that are hairless or they have lines of hair; the
stems and leaf undersides of Drummond's Aster are evenly pubescent. Some
authorities consider the preceding species of Asters to be varieties of each
other, in which case the Blue Wood Aster is the typical variety, Aster
cordifolius cordifolius. Another woodland species, Aster shortii
(Short's Aster), is also similar to Blue Wood Aster in appearance, but Short's
Aster has larger flowerheads (¾–1" across) and its leaves are
smooth to slightly serrated along their margins.