This erect summer annual flowers from August through October, spreading allergy-causing pollen in the air.
The 4 to 10 cm long leaves are hairy, and are generally egg shaped once or twice compound. The leaves are alternate, although the lower leaves are occasionally opposite. The hairy stem can be green to pinkish red.
This plant can be identified by the purple color found on the undersides of its cotyledons. It is similar to giant ragweed, just smaller.
Flower Seed Head:
The flowers occur in small clusters on terminal branches. Male and female flowers occur in different parts of the plant, with male flowers occurring in long, slender racemes, and females at the leaf axils.
A single seed forms in each 3 to 4 mm long achene. The achenes have longitudinal ridges that terminate in short spikes. The achenes have been known to survive for over 80 years in the soil.
This plant prefers full sun, and slightly dry conditions. It can be found growing in disturbed areas such as fields, pastures, and roadsides.