Polygonum arenastrum, commonly known as equal-leaved knotgrass,[2] is a summer annual flowering plant in the knotweed family Polygonaceae.

The numerous wiry stems grow out from the center of the plant giving it a mat-like appearance.

Common knotweed germinates at or near the soil surface in early spring, as soon there is enough moisture, and grows in an upright position before it spreads out like a mat.

The seeds, which grow low to the ground, survive mowing and are not disturbed when stepped on by people and animals.

Knotweed is a weed of waste areas but has been showing up in grain fields, where is becomes problematic because of its prolific seed production and long viability.

Covering garden beds with landscaping fabric and then mulch is a good way to keep knotweed from taking over.