Virginia Tech Weed Identification Guide

Common Ragweed: Ambrosia artemisiifolia

Weed Description: Summer annual, 0.2-2.5 m tall, found throughout the United States, producing abundant pollen that is a primary cause of hay fever.

Leaves: Leaves are 4 to 10 cm long, egg-shaped in outline and once or twice compound (pinnatifid).  Leaves hairy on upper surface and margin, densely appressed on lower surface.

Seedling: Stems below cotyledons (hypocotyls) are green, usually spotted with purple.  Cotyledons are roundish to oblong, purple underneath.  Young leaves opposite, becoming alternate with age, dense pubescence over entire leaf surface.

Stems:  Erect, branched, with long, rough hairs.

ambel3-19.jpg (158264 bytes)
cragweed9-20b.jpg (85557 bytes) Flowers: Flower heads small (2-4 mm broad), green, and arranged in slender inverted racemes at the ends of branches.  Male and female flowers are in separate heads on the same plant, the male flowers, usually drooping, are at the top of the plant, while the female flowers are in the upper leaves and bases of leaves.
Roots: Shallow taproot.

Fruit:  Woody achene, yellowish- to reddish-brown, 3-4 mm long and 1.8-2.5 mm wide, 1-2 mm central protuberance surrounded by 4-7 shorter projections.  Resembles a crown.

 

ragweed9-20a.jpg (166309 bytes) Identifying Characteristics: Cotyledons with purple underside.  Fruit an achene resembling a queen's crown.