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: Vermont and Massachusetts to
Manitoba and the Dakotas, southward to Louisiana and New Mexico. Habitat: Wet meadows, swamps, and marshes, sides of ditches.
Water Hemp has somewhat the appearance of a large, succulent Amaranth. Stem smooth, erect, sometimes nearly an inch in diameter at the base and attaining ten feet or more in height, but more often three to six feet tall, with many slender, flexuous branches. Leaves two to six inches long, lance-shape approaching to rhombic, entire, smooth but with prominent pinnate veins, and pointed at both ends; petioles slender and shorter than the blades. Flowers dioecious, in dense terminal or axillary spikes, sometimes interrupted and leafy, each small and greenish blossom guarded by one to three awl-like bracts. The sterile flowers have five stamens and five sharp-pointed, erect, one-nerved sepals, longer than the rigid bracts; the pistillate flowers are without a calyx and have a one-celled, one-seeded ovary with two to five plume-like stigmas. The small, shining seed drops from its place while still enclosed in an egg-shaped, valveless, and tuberculate Utricle, which makes it buoyant and easily distributed by wind and water. (Fig. 78.)
Fig. 78. - Water Hemp (Acnida tuberculata). X 1/4.
Prevention of seed development by close cutting or pulling while in early bloom. Drainage and cultivation of the ground.