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Common ragweed, Ambrosia artemisiifolia

 

Family: Asteraceae (Sunflower)

Group: Dicot

Life span: Annual

Origin: North America

Growth form: Forb/herb

Erect summer annual, 1 to 6 feet tall, with branched, hairy stems.  Leaves are sometimes opposite near the base and alternate towards the apex. Petioles are conspicuous on lower leaves but sometimes inconspicuous on the upper leaves. Leaves narrow to broadly egg-shaped in outline, hairy and deeply twice dissected or compound. Flowers are small, green and inconspicuous in clusters on terminal branches. Male flowers look like inverted cups and are in long spikes at the end of branches. Female flowers are in clusters in the axils of upper leaves and branches. Has a shallow fibrous root system with a taproot. Propagation is by seed. Common ragweed pollen is a primary cause of hay fever.

Often confused with ragweed parthenium (side by side photo)