Common ragweed Ambrosia artemisiifolia L.
Family: Asteraceae (Composite family)
Life cycle: Annual
Native status: Native to North America
Habitat: Crop fields, waste areas
General description: Erect plant up to 6 ft tall. Leaves are triangular in shape and finely divided, hairy. First leaves are opposite, but later leaves are arranged alternately. Male (staminate) flowers are on terminal racemes, whereas female (pistillate) are in axillary clusters below staminate flowers.
Key ID traits: Pubescent stems and leaves, finely divided leaves.
Similar species: Western ragweed is a perennial with leaves that are not as deeply divided as common ragweed. Leaves look somewhat similar to those of wild carrot or poison hemlock, but the latter are biennials and leaves are arranged in a basal rosette rather than an elongated stem.
Miscellaneous: Common ragweed is a major cause of hay fever.