Ambrosia trifida

giant ragweed, great ragweed, texan great ragweed, tall ragweed, blood ragweed, perennial ragweed, horseweed


Leaf Arrangement


Leaf Attachment


Leaf Margin


Leaf Type


Growth Form


Flower Color

green, inconspicuous, yellow

Flower Month

August - November

Height (meters)

1.0 - 5.0

Milky Sap








Growing Season

Warm season

Wetland Class


Wetland Coefficient of Conservatism


Prairie Coefficient of Conservatism


Field Characters

Easily distinguished in the field by its giant stature, 3-lobed leaves, and a clear red sap which exudes from cut stems. Seedling identification: Underside of cotyledons (seed leaves) is deep purple. Stem below seed leaves is usually green with purple splotches. Densely hairy over entire leaf surface.

Cultural Information

The seeds of this species are thought to be dormant at maturity. Germination benefits from moist stratification at 5 degrees C for 3 months (Davis 1930).

Animal Use

A high-use forage plant for white-tail deer in spring and summer. Deer and horses also eat giant ragweed. Ragweed seeds are one of the most important quail foods based on volume consumed. The following Information is for the genus Ambrosia with notation that A. artemisiifolia and A. psilostachya are the most useful to wildlife while A. trifida is of little value: Animals that eat its seeds: Yellow rail, Wilson snipe, Ground dove, Mourning dove, Attwater's prairie chicken, Bobwhite quail, Wild turkey, Woodcock, Redwing blackbird, Cardinal, Purple finch, Eastern goldfinch, Chipping sparrow, English sparrow, Harris sparrow, Eastern lark sparrow, Lincoln sparrow, Savannah sparrow, Tree sparrow, Eastern vesper sparrow, White-crowned sparrow, Meadow mouse, and White-tailed deer. Animals that eat its foliage: White-tailed deer and cottontail rabbit (Martin et al. 1951).

Natural History

A common weed all over the U.S. in rich alluvial soils. The pollen of ragweed is a major allergen and irritant to hay fever sufferers. Ragweed blooms in the fall at the same time as Senecio glabellus (yellowtop or butterweed) and Solidago canadensis (goldenrod) which are showy and often gets the blame for allergic reactions and hay fever. Ragweed is wind pollinated and consequently has inconspicuous flowers. The Acadians of south Louisiana call this plant "herbe du sang" or "bloodweed", referring to the red sap which exudes from cut stems (Holmes 1990). Cajun tradition claims that bloodweed grew under the cross during the crucifixion of Jesus. The genus name ambrosia comes from the Greek "ambrotos" for immortal and refers to the Greeks' belief that this plant has special powers. Trifida means "3 parts" and refers to the leaves which have 3 lobes. The seeds of this species have been found stored in caves along with other edible seed leading scholars to believe that the seeds were once used as food. Little is known about how Native Americans used these seeds (Kindscher 1987).


Waste places, fields, and roadsides.