Polygonum aviculare subsp. depressum — Overview

Oval-leaf Knotweed learn more about names for this taxon

IUCN threat status:

Not evaluated

Comprehensive Description

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This adventive annual plant is more or less prostrate, producing hairless stems up to 3' long. The alternate leaves are up to 1" long and 1/3" across. They are oblong or oblong-elliptic, smooth along the margins, and hairless. At the base of each leaf, there is a membranous sheath (ochrea) that wraps around the stem and hides the short petiole. This sheath becomes ragged and brown with age. The foliage of Prostrate Knotweed is often blue-green in appearance. A small cluster of 1-5 nearly sessile flowers occurs at the base of each leaf toward the growing point of each stem. Each tiny flower is about 1/10" long, consisting of 5 sepals, a style with a tripartite tip, 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 2-3 months. These flowers open for only a short period of time when the weather is hot and sunny. A 3-angled achene develops within the sepals of each flower. This achene is reddish brown or brown and tapers at one end more abruptly than the other. A fine membrane often clings to the surface of this achene. The root system consists of a slender shallow taproot that frequently branches. This plant spreads by reseeding itself. Different varieties of Prostrate Knotweed have been described, which are sometimes regarded as separate species.


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© John Hilty

Source: Illinois Wildflowers

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