Stem. - One to three feet high, smooth, branching. Leaves. - Alternate, narrowly lance-shaped or oblong. Flowers. - White or flesh-color, small, growing in erect, slender spikes. Calyx. - Five-parted. Corolla. - None. Stamens. - Eight. Pistil. - One, usually with three styles.

These rather inconspicuous but very common flowers are found in moist places and shallow water.

The common knotweed, P. aviculare, which grows in such abundance in country door-yards and waste places, has slender, often prostrate, stems, and small greenish flowers, which are clustered in the axils of the leaves or spiked at the termination of the stems. This is perhaps the " hindering knotgrass" to which Shakespeare refers in the "Midsummer Night's Dream," so terming it, not on account of its knotted trailing stems, but because of the belief that it would hinder the growth of a child. In Beaumont and Fletcher's "Coxcomb" the same superstition is indicated:

We want a boy Kept under for a year with milk and knotgrass.

It is said that many birds are nourished by the seeds of this plant.