Each flower spike is made up of many individual flowers. Flowers appear in July and may continue into September. Each mature plant can produce up to 2.7 million seeds annually. As tiny as grains of sand, seeds are easily spread by water, wind, wildlife and humans. Germination can occur the following season, but seeds may lay dormant for several years before sprouting.
Leaves are downy, with smooth edges.
They are usually arranged opposite each other in pairs which alternate down the stalk at 90 angles, however, they may appear in groups of three. Stalks are square or five or six-sided, woody, and up to six or more feet tall. Several stalks grow on mature plants. Rootstocks of mature plants are extensive and can produce up to 50 shoots, creating a dense web above and below ground which chokes out other plant life. The entire plant must be removed to minimize the chance for regrowth.