Giant Ragweed, Great Ragweed

Ambrosia trifida L.

Asteraceae (Sunflower Family)


Giant Ragweed is an annual that frequently exceeds 10 feet or 3 meters tall in moist locations. In drier areas, it may mature at a smaller height. Its stems and leaves are rough. The leaves have long petioles, are opposite each other, and are attached to a single center stem. They usually are divided into three lobes but can have five or none. The flowers are either male or female and are located in clusters at the top of the plant; they often exceed 6 inches in length. Shortly after flowering in the fall, the pollen spreads and causes many people to have hay fever problems. The seeds are 0.25 inches long and have four or five terminal spikes on each.


Giant Ragweed is found in moist areas near roadsides, fields, and disturbed sites. It is found throughout most of North America except for the far North.