Description: This native annual or biennial
plant is 1-4' tall, branching occasionally. The green or reddish stems
are slightly hairy. The alternate compound leaves are oddly pinnate, dividing
into 3-7 slender segments. Each compound leaf is up to 8" long and 4" across,
and is much broader at the base than toward the outer tip. The leaflets are
slightly ciliate coarsely dentate, or cleft into shallow pointed lobes. At the
ends of major stems, or from the axils of upper leaves, can appear from 1 to 3
compound flowers. A plant will often have several of these flowers in bloom at
the same time. Each daisy-like compound flower is about 2" across, and consists
of 8-10 yellow ray florets surrounding numerous golden yellow disk florets.
Each compound flower is subtended by 12-20 involucral bracts that are each
about ¾" long, coarsely ciliate, and rather contorted. The blooming
period occurs from late summer to early fall and lasts about a month. The
flowers are slightly fragrant, which becomes quite noticeable in a large
colony. The dark brown achenes are rather flat, rough-textured, and have a
central longitudinal ridge. Each achene is about 1½–2 times long as
it is wide, with two tiny awns at the top that are barely visible. This
contrasts with other Bidens spp., which have 2-4 awns that are long and
conspicuous on the apex of each achene. The root system consists of a shallow
branching taproot.
Cultivation: The
preference is full sun and wet to moist conditions. The soil should be rich in
organic material. This plant is easy to grow, but tends to be aggressive at a
disturbed site that is sunny and moist. It can form large colonies by reseeding
itself. This species of Bidens appears to be more tolerant of hot dry
weather than many others.
Range &
Habitat: The Long-Bracted Tickseed Sunflower is occasional in the
southern half of Illinois and NE Illinois, but it is rare or absent in the
remaining northern counties (see
Distribution
Map). Habitats include moist black soil prairies, gravelly seeps, ditches
along railroads and roadsides, muddy fields, and miscellaneous waste areas. It
usually occurs in or around poorly drained areas that are prone to standing
water, or near sources of more or less permanent water. Disturbed areas are
favored because of reduced competition from deep-rooted perennial
plants.
Faunal Associations: The
flowers are popular with many kinds of insects, including long-tongued bees,
short-tongued bees, wasps, flies, butterflies, skippers, and beetles. Typical
bee visitors include bumblebees,
Epeoline Cuckoo bees, Miner bees, large
Leaf-Cutting bees, Green Metallic bees, Plasterer bees, and Panurgine bees. The
caterpillars of the butterfly Nathalis iole (Dainty Sulfur) are known to
favor the foliage of Bidens spp. as a food source. The caterpillars of
several moths feed on the foliage or the pith of stems, including Epiblema
otiosana (Bidens Borer Moth), Platysenta mobilis (Mobile
Groundling), Condica confederata (The Confederate), Cirrhophanus
triangulifer (Goldenrod Stowaway), and Palthis asopialis
(Faint-Spotted Palthis). The seeds are eaten by small rodents and various
birds, including the Ring-Necked Pheasant, Bobwhite, Swamp Sparrow, and Purple
Finch. The foliage is eaten occasionally by the Cottontail Rabbit. Even though
their awns are tiny, the achenes of Bidens polylepis can cling to the
the fur of animals or clothing of humans; this is largely because of their
rough edges. Small rodents may carry the achenes to their dens some distance
from the mother plant.
Photographic
Location: The photographs were taken at Meadowbrook Park in Urbana,
Illinois.
Comments: This is one of
the prettier and more drought tolerant Bidens spp. that occasionally
strays from wetlands to moist prairies. The Long-Bracted Tickseed Sunflower can
be distinguished from other Bidens spp. by its attractive flowers and
slender pinnate foliage. It has a very similar appearance to Bidens
aristosa (Tickseed Sunflower). However, this latter species has only 8-11
involucral bracts that are shorter and less hairy than Bidens polylepis.
Furthermore, the typical achene of Bidens aristosa is more than twice as
long as it is wide, and it has a pair of long barbed awns at the top. Because
of these differences, the Long-Bracted Tickseed Sunflower is classified as a
distinct species. In the past, it has been assigned such scientific names as
Bidens aristosa var. retrorsa and Bidens involucrata.