Description: This native perennial plant is 1½–3' tall, and largely unbranched except at the inflorescence. The central stem is light green and largely hairless. Near the base of the plant, are basal leaves with long narrow petioles. These basal leaves are about 3" long and 1½" across, cordate or broadly oval, and largely hairless. Their petioles are about 1½" long and finely pubescent, while their margins are smooth, or nearly so. As the leaves alternate upward along the stem, they become greatly reduced in size and more narrow. These upper leaves are narrowly lanceolate, narrowly elliptical, or linear; they are sessile against the stem.
The inflorescence is a large panicle of
compound flowers that are daisy-like in appearance; this large inflorescence
has a tendency to droop over somewhat. The compound flowers are about ½"
across or slightly larger. They consist of about 10-25 lavender or light blue
ray florets, which surround numerous disk florets that are initially yellow,
but later turn red or brown. The compound flowers are subtended by numerous
bracts that are ciliate and form small green diamonds. The blooming period
occurs from late summer to fall, and lasts about 1-2 months. Later, achenes
develop with small tufts of hair, which are dispersed by the wind. The root
system is fibrous and rhizomatous; older plants may develop a short
caudex.
Cultivation: The preference
is full or partial sun and mesic to dry conditions. This plant is rather
indifferent to soil characteristics, and can flourish in soil that loamy,
sandy, rocky, or contains clay. This plant is easy to grow and drought
resistant; the lower leaves are occasionally marred by powdery mildew and other
foliar diseases.
Range &
Habitat: Sky Blue Aster occurs occasionally in the northern and
western halves of Illinois, but is uncommon or absent elsewhere (see
Distribution
Map). Habitats include mesic to dry black soil prairies, rocky upland
woods, savannas, woodland borders, sandy meadows, limestone glades, clay banks,
and areas along roadsides.
Faunal
Associations: The flowers attract various insects, including small
bees, flies, small to medium-sized butterflies, skippers, and wasps. Among
these, Green Metallic bees and other Halictid bees are especially common
visitors of the flowers, where they seek nectar or pollen.
The caterpillars of the butterfly Chlosyne nycteis (Silvery Checkerspot)
and several species of moth feed on this and other asters (see
Moth Table). The Wild Turkey and been
observed feeding on the foliage and seeds of asters to a limited extent. Many
mammalian herbivores occasionally eat this plant, even though it has low food
value, including rabbits, deer, groundhogs, and livestock.
Photographic Location: The photographs were taken at
the webmaster's wildflower garden in Urbana, Illinois.
Comments: For the size of the plant, the
inflorescence of Sky Blue Aster is rather large and showy. This species of
aster closely resembles Aster shortii (Short's Aster), even though the
latter is a woodland species. However, the upper leaves of Short's Aster are
often cordate, rather than narrowly lanceolate or linear, and its flowers are
slightly larger in size. Another similar species, Aster laevis (Smooth
Blue Aster), doesn't have any cordate or broadly oval leaves at the base of the
plant, unlike Sky Blue Aster, and the flowers of the former species tend to be
slightly larger in size as well. In distinguishing the different species of
asters, it is often useful to consider the shape of the leaves (especially the
basal leaves), and the presence or absence of fine hairs on the foliage and
stems. Another scientific name for this plant is Aster
azureus.