This plant is a summer annual about 1-4½' tall, branching occasionally.
The stems are light green to purple, more or less terete, and glabrous.
Leaves are usually opposite, although some of the uppermost leaves may
be alternate. The leaf blades are 2-6" long and ½-1½" across;
they are lanceolate to oblong-lanceolate and coarsely serrated along
their margins; some of the lower leaves often have 1-2 smaller basal
lobes. The upper blade surface is medium green and glabrous, while the
lower blade surface is pale-medium green and glabrous. During the
autumn, the leaf blades often become purplish green or purple. The
petioles are up to 2" long and usually narrow, although some of them
may be partially winged.
The upper stems terminate in 1-3 flowerheads each
on peduncles about ½-4" long. The peduncles are light green or purplish
green, more or less terete, and glabrous. Each flowerhead spans ½-1¼"
across (excluding the leafy bracts), consisting of numerous disk
florets and usually no ray florets. When ray florets occur, they are
insignificant and few in number. The corollas of the disk florets are
yellow to orange, narrowly tubular in shape, and about 3 mm. (1/8")
long; each corolla has 4-5 recurved to ascending lobes along its upper
rim. The disk florets are perfect,
while the ray florets, if they are present, are sterile. Surrounding
the disk florets are about 8 floral bracts (phyllaries) that are
yellowish brown or yellowish black, ovate in shape, and glabrous; they
are about 6 mm. (¼") long.
Originating from below both the disk florets and floral bracts, but
spreading outward, there are 3-8 leafy bracts about ½-1½"
The leafy bracts are green, glabrous, and oblanceolate, elliptic, or
oblong in shape. The blooming period occurs from late summer into the
fall, lasting about 1-2 months. The disk florets are replaced by awned
achenes that are about 5-6 mm. in length (excluding the awns),
oblanceolate in shape, and somewhat flattened. At the apex of each
achene, there are 4 barbed awns consisting of two longer outer
awns (about 4 mm. in length) and two shorter inner awns (about 2 mm. in
length). However, because the 2 inner awns are fragile and often become
detached, some achenes will have only 2-3 awns (or even less,
should the outer awns become detached). The root system consists of a
shallow branching taproot. This plant reproduces by reseeding itself,
occasionally forming colonies.
The preference is
full sun to moderate shade and wet to moist conditions. Various types
of soil are tolerated, including those that contain loam, silt, and
clay. This plant is somewhat weedy.
native Purple-Stemmed Tickseed is occasional in the northern half of
Illinois, becoming uncommon or absent in the southern half of the state
Habitats consist of marshes, muddy areas of
seasonal wetlands, streambanks, swamps, and ditches. Areas with a
history of disturbance from flooding or other causes are preferred.
Robertson (1929) observed bumblebees sucking
the flowerheads of Purple-Stemmed Tickseed. It is also likely that
Halictid bees and miscellaneous flies also visit the flowerheads for
nectar or pollen. The following aphids suck plant juices from this and
other Bidens spp.
The following leaf beetles feed on these plants
and similar members of the Aster family: Calligrapha bidenticola
and Calligrapha elegans
Other insects include foliage-consuming caterpillars of the
butterfly Nathalis iole
and flowerhead-consuming larvae of the fruit fly Icterica
. The caterpillars of several
moths feed on the foliage, feed on the flowerheads, or bore through the
stems of Bidens
. These species include Cirrhophanus
(Goldenrod Stowaway), Condica
(The Confederate), Condica mobilis
(Mobile Groundling), and Epiblema
(Bidens Borer Moth). Some vertebrate
animals also feed on these plants. Such turtles as Chelydra serpentina
(Snapping Turtle), Chrysemys
(Painted Turtle), and Emys
(Blanding's Turtle) eat the foliage or seeds
(Ernst et al.,
1994; Lagler, 1943). Several ducks, upland gamebirds, and granivorous
songbirds also eat the seeds, including such species as the Wood Duck,
Mallard, Black Duck, Wild Turkey, Ring-Necked Pheasant, Greater Prairie
Chicken, Bobwhite Quail, Purple Finch, Common Redpoll, Swamp Sparrow,
Pine Grosbeak, and Eastern Goldfinch (Martin et al., 1951/1961;
Eastman, 2003). The foliage is eaten by the White-Tailed Deer and
Cottontail Rabbit, although it is not a preferred source of food.
Because the barbed awns of the achenes can cling to the fur of animals
and the clothing of humans, they can be carried considerable distances
to new locations.
A shaded streambank at Meadowbrook
This plant and other Bidens
are occasionally parasitized by
various Cuscuta spp.
(Dodders); the latter are vine-like plants without
chlorophyll that often occur in wetlands. Because its ray florets are
insignificant or absent, Purple-Stemmed Tickseed is one of the less
showy species in this genus. It is relatively easy to confuse this
species with other species in this genus that share this
characteristic. In particular, Bidens
is similar in appearance. This latter species can be distinguished by
the shorter petioles of its leaves (which are often winged), its longer
leafy bracts (up to 2½" long), and the yellowish color of its stems. In
addition, the corollas of the disk florets for this species have 4
lobes more often than 5 lobes, while the reverse is true for
Purple-Stemmed Tickseed. The achenes of Purple-Stemmed Tickseed are
also distinct: each of its achenes has 2 long outer awns and 2 short
inner awns, although these awns (particularly the inner ones) often