This is a native annual plant up to 3' tall and branching frequently. The hairy stems are green to light pinkish red. The leaves are up to 6" long and 4" across, and are opposite or alternate along the stems. They are deeply pinnatifid, broadly lanceolate (in outline), and usually much wider at the base than the tip. Mature leaves are relatively hairless, but small emergent leaves often have hairs on their undersides. Many of the upper stems terminate in one or more cylindrical spikes of flowers about 1-4" long. Near the base of the central flowering spike, one or two small spikes may develop that are only half as long. The small flowers are initially green, but later turn yellowish green or brown as they mature and develop into achenes. Each flower is about 1/8" long, the males producing a fine yellow pollen that is easily carried by the wind. This pollen is usually released during late summer or early fall. Numerous seeds are produced, which can remain viable for 5 years or more. The extensive root system is fibrous.