Description: This plant is a summer annual with branched stems up to 2' long; it is more or less prostrate. The rather succulent stems are rather terete, smooth, and glaucous; they vary in color from whitish green to pale red. The alternate leaves are up to 2" long and half as much across; they are dark green, glabrous, obovate (spoon-shaped), and smooth along the margins. Each leaf tapers gradually to a slender petiole.
Short clusters of
light green flowers develop from the axils of the leaves. Each plant is
monoecious and produces separate male (staminate) and female flowers
(pistillate). The male flowers have 4-5 sepals, 3 stamens, and no
petals, while the female flowers have 4-5 sepals, an ovary with 3
styles, and no petals. The sepals of both kinds of flowers are about
1/8" (3 mm.) in length or a little longer and oblong-lanceolate in
shape.
Underneath the flowers, are several bracts that are the same length or
a little larger than the sepals. Like the sepals, the bracts are light
green and oblong-lanceolate; their tips are pointed, but not spiny. The
blooming period occurs from early summer into the fall; individual
plants can bloom for about 1-3 months. The flowers are wind-pollinated.
Each flower is replaced by a bladder-like capsule (or utricle)
containing a single seed; this capsule is globoid and smooth while
young. Later, it splits open around the middle to release the seed. The
seeds are 1–2 mm. across; they are dark brown or black, shiny,
round in circumference, and somewhat flattened. The root system
consists of a stout taproot. This plant spreads by reseeding itself.
Cultivation:
This plant is typically found in sunny areas where the soil is moist or
mesic, loamy, and fertile. It is quite weedy. The seeds can remain
viable in the ground for at least 10 years.
Range & Habitat:
The adventive Prostrate Pigweed is quite common in most areas of
Illinois, except the
NW and SE sections of the state, where it is apparently less common or
absent. Prostrate Pigweed is native to the western United States.
Habitats include fields, cropland, gardens, vacant lots, construction
sites, landfills, areas along railroads and roads, and waste areas.
This plant prefers highly disturbed habitats with bare open ground; it
is not invasive of natural habitats in Illinois.
Faunal Associations: The foliage,
seeds, and other parts of Prostrate Pigweed (Amaranthus blitoides) and
other amaranth/pigweeds (Amaranthus spp.) are eaten by various insects,
including flea beetles, seed-eating ground beetles, weevils,
leaf-mining larvae of Anthomyiid flies, plant bugs, aphids,
caterpillars of Tiger moths and other moths, and grasshoppers. Two
skippers, Pholisora catullus (Common Sootywing) and Staphylus
hayhurstii (Hayhurst's Scallopwing), also feed on these weedy plants (see Insect Table for a more complete list of these species).
The seeds are eaten by the Greater Prairie Chicken, Mourning Dove, Horned Lark,
Savannah Sparrow, and many other granivorous birds (see Bird Table for a listing of these species). The foliage of
Prostrate Pigweed is eaten by rabbits, pigs, and poultry (Georgia, 1913).
Photographic Location:
A construction site near the Champaign County Courthouse in Urbana,
Illinois. The plant in the photograph isn't blooming.
Comments: This
is a typical field weed. Prostrate Pigweed is easy to identify because
of its prostrate habit and spoon-shaped leaves. Other Amaranth
spp. (Pigweeds, Amaranths) in Illinois are more erect and
their leaves are more lanceolate in shape. An exception is Amaranthus
tuberculatus var. prostratus (Prostrate Water Hemp). This
rare plant has a prostrate habit, but its leaves are lanceolate, rather
than spoon-shaped, and its female flowers have fewer sepals. Prostrate
Pigweed superficially resembles Portulaca oleracea
(Common Purslane). However, this latter species produces small flowers
with yellow petals and its leaves lack the conspicuous lateral veins
that can be found on the leaves of Prostrate Pigweed. Some authorities
use the scientific synonym Amaranthus graecizans
for Prostrate Pigweed.