Ambrosia trifida L.

Giant Ragweed; Great Ragweed

Herb

Annual

Vascular

Giant Ragweed is a native herbaceous annual in the Sunflower family (Asteraceae). It can be found throughout Alabama. Giant Ragweed occurs along rivers and streams, along woodland margins, and in disturbed areas. It is an annual with a tap root. The stems are erect, branched, 3-12 feet in height, green in color, and ribbed. The leaves are opposite, petiolate, ovate to elliptic in outline, (un-lobed) palmately 3-5 lobed, with serrate margins. The leaves are pubescent with stiff hairs and gland dotted. Flowers are in heads. The staminate heads are arranged in terminal spikes or racemes. Pistillate heads occur in fascicles in the axils of the upper leaves. The staminate heads are stalked with a saucer shaped involucre. The staminate heads have 3-25-disc flowers, and the pistillate heads have a single disc flower. The flowers are yellowish-green in color. The fruit is a dark brown, beaked nutlet with a tough seed coat. The seed may remain dormant in the soil for many years awaiting a disturbance. The pollen of this plant is a major cause of hay fever. Giant Ragweed was cultivated by pre-Columbian Native Americans for the edible oil obtained from the seed. Seed from archaeological sites are 3-4 times as large as those of wild plants occurring today, indicating that they were selected for their size.--A. Diamond

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Native FAC (NWPL)

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