South Dakota Native Plant Research
Asteraceae : Ambrosia trifida

Asteraceae : Ambrosia trifida


Download Ragweed plant (3.7 MB)

Download Flowers (756 KB)

Download Large stand of ragweed. (1.2 MB)

Family Name


Common Name

Giant Ragweed


Ambrosia trifida is an annual herb growing up to 2 m tall, but may reach over 6 m in rich, moist soils. The stem has a woody base and are branched or unbranched. Leaves are mostly oppositely arranged, with blades that are variable in shape, usually palmately lobed, and often with toothed edges. The largest leaves can be over 25 cm long and 20 cm wide, with petioles several centimeters long. They are glandular and rough in texture. The flowers are arranged in a spike, monoecious, with plants bearing inflorescences containing both pistillate and staminate flowers. Staminate flowers are yellow to greenish with no petals, about 3mm across, hanging down on short stalks along the spike. Pistillate flowers are indistinct, hidden in clusters of short leafy bracts. The fruit is a bur a few millimeters long tipped with several tiny spines.

Additional Notes

Ragweed is an early pioneer species of disturbed soils and is a very aggressive species. Ragweed produces large amounts of highly allergenic pollen and is a major contributor to hay fever for many people.

Horticulture Notes

This species is often considered a noxious weed and is not recommended for cultivation.

Asteraceae : Ambrosia trifida