Prostrate knotweed is a prostrate, summer annual or perennial weed in the buckwheat family and originally from Eurasia. It grows in fields and wetlands, in both high and low elevations, throughout the world and in all 50 states of the United States. Each plant is capable of producing thousands of seeds that stay viable for several years. The plant grows low to the ground on long stems up to 3 feet long and mowing is ineffective as a control. The foliage is often a blue green and small flowers, that only open in hot, sunny weather, occur at the base of each leaf. The genus name is Greek for "many knees", in reference to the prominent nodes along the stem. The species name means "little bird" because the fruits resemble a bird's beak. Prostrate Knotweed prefers full sun and moist to dry, heavy soil. It does well in poor soil, including heavily contaminated ones. It tolerates a fair amount of trampling. The plant has a slender shallow taproot that frequently branches and the plant spreads by reseeding itself. Diseases, Insect Pests, and Other Plant Problems: Prostrate Knotweed can be a problem for grain and crop fields, lawns and cities where it grows in the cracks of pavement and along roads.
Curated pairwise relationships between this plant and others in the library — who feeds
whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.
No curated interactions recorded for this species yet.
Also noted by NC State
Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell
apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.
One inch by 1/3 inch oblong green to blue-green, smooth, alternate leaves with entire margins. A membranous sheath (ochrea) wraps around the stem at the base of each leaf.
Flower color
Pink; White
Flower form
Cyme
Flower shape
Radial; Tubular
Flower size
< 1 inch
Flower detail
A small cluster of 1 to 5 tiny flowers appear in the axil of leaves near the stem end mid-summer to early fall. Each tiny flower consists of 5 sepals, several stamens, and no petals. The flat sepals have white margins, otherwise they are green, pink, or purple. The flowers bloom from mid-summer to early fall for 2 to 3 months, but open for a short period when the weather is hot and sunny.
Bloom time
Fall; Summer
Fruit color
Brown/Copper
Fruit type
Achene
Fruit size
< 1 inch long, < 1 inch wide
Fruit detail
A 3-angled brown achene develops within the sepals of each flower. This achene tapers at one end and a fine membrane often clings to the surface.
Stem color
Green
Stem detail
Stem is wiry, matted, branching, and prostrate to erect.
Wildlife & Ecology
Native status
Non-native
Origin
Macaronesia and Eurasia
Distribution
Temperate regions worldwide.
Wildlife value
Food plant for caterpillars.
Food & Medicine
Edible parts
Seeds
Harvest time
Fall; Summer
Fruit type
Achene
Edibility
Seeds edible raw or ground into a flour
Uses (ethnobotany)
Parts of the plant used medicinally and the leaves are sometimes used to produce blue or green dye.