Great Ragweed (Ambrosia trifida)

Great Ragweed (Ambrosia trifida)

Great Ragweed (Ambrosia trifida), also known as the Giant Ragweed is an annual forb/herb in the order Asterales and Asteraceae (Aster/Sunflower) family that can grow as high as 15 feet (4.5 meters) but is normally around three feet (one meter) high. at maturity in the area of French Hill Pond.1,2 The genus name is from the Latin for "healing plant." The species name is from the Latin for "having three parts'" referring to the normally three lobed leaf. Native Americans used this plant for medicine but it is best known as an allergen causing hay fever. One of the few uses of this plant is as a compost activator, a use to which it should be relegated as soon as possible.3

The flowers are small, green and hairy. Male (staminate) and female (pistillate) flowers exist on the same plant. Such a plant is said to be "monoecious." The male flowers are at the top of a flower spike and are yellow-green in color. The female flowers are at the bottom of a spike near the leaf axis and are greener in color. A flower spike can be up to ten inches (25 centimeters) long. The pollen from these flowers is a primary cause of hay fever in people.1,3

Great Ragweed (Ambrosia trifida) Detail

The leaves are green, opposite and palmate with three to five lobes. The leaf blades can vary in shape from elongated ovate to lance-shaped. The margins are smooth to somewhat toothed. The length of a leaf can be up to about nine inches (23 centimeters) long and eight inches (20 centimeters) wide.1,3

The fruit is a pale-tan, beaked, bur-like seed tipped with spines about 0.2 inches (5 millimeters) long.1,2,3

The root system is simple.

.This plant flowers from June through October.1


1. Niering, William A. and Nancy C. Olmstead, "The Audubon Society Field Guide to North American Wildflowers," Alfred A. Knopf, New York, 1988

2. United States Department of Agriculture, Plants Database,, 2/10/2016

3. Wikipedia, the free encyclopedia,, 2/10/16


Field Plants Technical Data and Information French Hill Pond Home