Description: This is a native annual plant with a
large and stout central stem from 3-9' tall, although occasionally smaller.
Toward the apex of the plant, there
may be a few side stems, but it is tall and columnar
overall. The large alternate leaves are up to 8" long and 6" across – they
have a tendency to droop downward from the long petioles. They are cordate with
fine dentate margins, although some of the smaller leaves may have smooth
margins and a lanceolate shape. The daisy-like composite flowers consist of
numerous central disk florets that are brown, which are surrounded by
approximately 20-40 ray florets that are yellow. Each composite flower is about
3-5" across. An average plant will bear from 1-10 of these flowers, and bloom
from mid- to late summer for about 1½ months. There is not much of a
fragrance, although the disk florets have a musty smell that is peculiar to
sunflowers. The roots of this annual plant are fibrous, while the seeds are
dispersed by gravity when the tall plants topple over during the winter. Like
many other species in its genus, the Annual Sunflower exudes chemicals that
kills off other kinds of vegetation. Thus, it has a tendency to form colonies
that exclude other plants, particularly in disturbed areas.
Cultivation: The preference is full sun, moist to
slightly dry conditions, and a fertile loamy soil. However, the annual
sunflower often thrives in soil with a high clay or gravel content. There is a
natural tendency for the lower leaves to shrivel and drop whenever there are
extended spells of hot dry weather. Powdery mildew sometimes attacks the leaves
during the fall, but this is usually after the plant has finished blooming and
is forming seeds. It is easy to start plants from seeds.
Range & Habitat: The Annual Sunflower occurs
throughout Illinois, and is especially common in the central and northern areas
of the State (see
Distribution
Map). It occurs in disturbed areas of mesic to dry prairies, woodland
meadows, cultivated and abandoned fields, pastures, areas along railroads and
roads, and urban waste areas. It may occur sporadically as individual plants,
or in small to large colonies that persist year after year. This annual plant
has little capacity to recover from summer wildfires, therefore it is morely
likely to flourish in their absence.
Faunal
Associations: Long-tongued bees are the most important pollinators,
including the honeybee, bumblebees, Miner bees, and Leaf-Cutting bees.
Halictine bees are important visitors, while visitors of lesser importance
include bee flies, butterflies, skippers, and the Goldenrod Soldier Beetle. All
of these insects seek nectar primarily. Syrphid flies and other beetles
occasionally feed on pollen, but they are usually non-pollinating. Also, many
insects feed on foliage and other parts of the Annual Sunflower (see
Table). Because the seeds are
abundant, large-sized, and nutritious, they are an attractive food source to
many animals, including upland gamebirds, songbirds, ground squirrels, tree
squirrels, and mice. To some extent, the seeds are distributed by these
animals. Mammalian herbivores, such as rabbits, ground hogs, and deer, may eat
the foliage, particularly from young plants. Muskrats and beavers eat the stems
and other parts, or they may use them in the construction of lodges and dams.
Photographic Location: The above
photographs were taken along a railroad near Champaign,
Illinois.
Comments: The Annual
Sunflower is thought to be adventive from western United States. However, it
was cultivated as a source of food by native Americans, and was likely
introduced to Illinois by them prior to European settlement. The cultivated
sunflower of modern agriculture is a self-pollinating hybrid of this plant and
another annual sunflower that occurs in the Great Plains. Because of its large
heart-shaped leaves, it is easy to distinguish the Annual Sunflower from other
Helianthus spp. that occur in the Midwest.