Time of bloom: June to October.
Seed-time: July to November.
Range: Nearly everywhere in North America, Europe, and Asia.
Habitat: Cultivated grounds, yards, roadsides, and waste places.
A social, almost domesticated, weed, seeming to thrive best where most trampled and abused, growing in thick mats along hard-beaten farmyard paths, and intruding persistently in lawns and garden borders; it often fringes the stone flags of city sidewalks.
Stems slender, pale green, faintly ridged, usually prostrate, four inches to nearly two feet in length, branching in all directions from the white, woody, rather deeply boring root. Smaller branches come out at many of the numberless "knots," or joints, which are pale under the sheathing stipules. Leaves bluish green, nearly elliptical in shape, sessile or with very short petioles, a quarter-inch to an inch long. Flowers very small, the calyx five-parted, greenish white with pink margins, sitting solitary or in groups of two or three in the leaf axils; stamens usually eight, sometimes fewer; style three-parted. Achenes dull brown, with acute apex and rounded base, three-angled, and minutely ridged. This species and also the one following is often attacked by a white mildew. (Fig. 57.)
Hoe-cutting or hand-pulling before the first seeds ripen. Dormant seeds will supply later crops to be treated in the same way until the ground is clean.
Fig. 57. - Prostrate Knotweed (Polygonum avicu-lare). X 1/2.