Description: This introduced grass is a summer annual about 2-5' tall. It often branches near the base, sending up multiple stems that are erect to ascending. The blades of the alternate leaves are up to 15" long and ¾" across; they are light to medium green, linear in shape, and rather floppy and drooping. The upper surface of each leaf blade often has scattered fine hairs that are stiff and bristly; sometimes the upper surface is shiny and nearly hairless. The margins of the leaf blades are rough-textured from minute teeth. The leaf sheaths are light green, pubescent to hairless, and open at the apex. Each ligule at the junction of the sheath and blade consists of a ring-like tuft of white hairs up to 3 mm. long.
Each stem terminates in a spike-like
panicle of florets up to 7" long. These spike-like panicles are very bristly in
appearance and nod downward towards their tips; they are initially light green,
but later become light brown to straw-colored. Each side branch of the panicle
is very short and inconspicuous; each branch has a few ovoid spikelets on short
pedicels. Each spikelet has a pair of glumes, a fertile lemma with a floret,
and 1-3 bristly hairs that originate from the base of the spikelet. The first
glume is about 1 mm. long, the second glume is about 2 mm. long, and the
fertile lemma is about 3 mm. long. The bristly hairs of each spikelet are
initially green, but later become light brown to straw-colored; they are up to
½" long. The floret of each spikelet has an ovary, 3 stamens, and a pair
of feathery stigmas. The blooming period typically occurs from late summer to
early fall; the florets are wind-pollinated. Each spikelet develops a single
grain during the fall that is pale-colored, ovoid in shape, and rather
flattened. The root system consists of a shallow tuft of fibrous roots. This
grass reproduces by reseeding itself. It often forms colonies of varying
size.
Cultivation: This grass is
typically found in sunny areas that are moist to dry. It adapts to many kinds
of soil, including those that contain loam, clay, silt, or gravel. The seeds
don't germinate until the weather becomes warm during the late spring or early
summer. Most vegetation growth occurs during the summer. In spite of its
shallow root system, Giant Foxtail is able to withstand considerable drought
because of its C4 metabolism. This grass can reseed itself aggressively and
become a pest where the ground is cultivated.
Range &
Habitat: Giant Foxtail is a common grass that occurs in every county
of Illinois. It was introduced into the United States from East Asia during the
1920's, probably in contaminated shipments of grain. This grass soon appeared
in Illinois, where it has spread relentlessly ever since. Habitats include
weedy meadows, degraded savannas, gravel bars in rivers, banks of drainage
canals, fallow fields, cropland, landfills, mined land, construction sites,
vacant lots, junk yards, sunny fence rows, edges of yards, gardens, areas along
railroads, roadsides, and waste land. Areas with a history of disturbance are
strongly preferred.
Faunal
Associations: The species Hysteroneura setaria (Rusty Plum
Aphid) sucks juices near the seedheads of Setaria spp. (Foxtail
Grasses). Rabbits, voles, and livestock occasionally eat the foliage of Foxtail
Grasses. However, the bristly seedheads of mature plants can damage the
mouthparts of horses and cattle. The seeds of Foxtail Grasses are eaten by the
Thirteen-Lined Ground Squirrel and many kinds of birds (see
Bird Table). Because of the
abundance of these weedy grasses and the popularity of their seeds, Foxtail
Grasses are one of the most important sources of food for
birds.
Photographic Location: Along
a railroad in Champaign, Illinois. The photographed grasses are leaning
sideways to a greater extent than usual.
Comments: Because of its large size and long nodding
seedheads, mature plants of Giant Foxtail are quite conspicuous. It is one of
several introduced Setaria spp. (Foxtail Grasses) that are weedy summer
annuals. Giant Foxtail is larger in size than other Foxtail Grasses that occur
in Illinois, and its seedheads are long and conspicuously nodding. Other
Foxtail Grasses in the state have seedheads that are straight or nod slightly.
The bristly hairs of Giant Foxtail's seedheads are always green before they
become light brown or straw-colored. In contrast, young bristly hairs of
Setaria glauca (Yellow Foxtail) are always yellow and those of
Setaria viridis (Green Foxtail) are sometimes purple. Another grass
species, Elymus canadensis (Canada Wild Rye), superficially resembles
Giant Foxtail because of its large size and nodding bristly seedheads. However,
the bristly hairs of Canada Wild Rye are even longer than those of Giant
Foxtail, and they curve outward from its seedheads. In contrast, Giant Foxtail
has straight bristly hairs on its seedheads.