Ragweed, giant (Ambrosia trifida)

An erect summer annual that can reach as much as 15 feet in height and thrives in fertile agricultural soils. Seedlings have cotyledons that are large, round and thick, three to four times larger than those of common ragweed. The first pair of true leaves is unlobed and lance-shaped with toothed margins. At this stage, the seedlings can be confused with common cocklebur. Subsequent leaves are large and distinctively three-lobed, or less often five-lobed. Leaves are opposite, hairy, and occur on long petioles. As with common ragweed, flowers are green and inconspicuous. Giant ragweed also produces a large, black crown-shaped achene that encloses the seed.

IPM1007, revised June 2007