Asteraceae : Ambrosia trifida
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Family Name
Asteraceae
Common Name
Giant Ragweed
Description
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.
Horticulture Notes
This species is often considered a noxious weed and is not recommended for cultivation.
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.