This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Annual. Propagates by seeds.
Time of bloom: July to September.
Seed-time: August to October.
Range: Maine to New Jersey on the Atlantic Coast; in the West from Minnesota to the Northwest Territory, California, Arizona, and New Mexico. Habitat: Sandy, often brackish, soil; irrigated lands, waste places.
Fig. 58.- Erect Knotweed (Polygonum erectum). X 1/2.
Stem rigidly upright, sometimes attaining four feet but more often six inches to two feet in height, much branched, slender, slightly ridged, and smooth. Leaves yellowish green, smooth, narrow lance-shaped, pointed at both ends, a quarter-inch to an inch long, with very short petioles conspicuously jointed to the collar-like stipules, which are funnel-form, thin, usually cut and torn. Flowers in axillary clusters, greenish with yellow margins; stamens three to six; sepals six, the three inner ones small, the outer ones larger, keeled and curving inward at the summit, persistent, their withered remains enfolding the smooth, shining, three-angled achenes when they mature and fall.
Means of control Prevent reproduction by cutting or pulling when in first bloom.