Kansas Wildflowers and Grasses

GIANT RAGWEED

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Ambrosia trifida L.

Johnson County, Kansas

Annual

Height: 3-13 feet

Family: Asteraceae - Sunflower Family

Flowering Period: August, September,October

Stems:

Erect, usually simple or sparingly branched above, longitudinal ridges, rough, short-hairy.

Leaves:

Mostly opposite, uppermost often alternate, simple, rough; stalks .4 to 2.8 inches long; blades of lower and middle leaves egg-shaped to nearly circular in outline, 4 to 8 inches long, 1.2 to 7.8 inches wide, usually palmately 3- to 5-cleft; margins usually toothed; upper surface somewhat spreading-hairy; lower surface nearly smooth; upper leaves smaller, 3-cleft to nearly entire.

Inflorescences:

Monoecious (staminate and pistillate heads occur at different locations on same plant); heads of staminate florets in racemes, elongated, to 6 inches long, panicle-like, terminal; heads of pistillate florets in clusters in axils of bracts below staminate inflorescences.

Flowers:

Greenish-yellow; staminate heads short-stalked, saucer-shaped, 1/12 to 1/6 inch across, 6-8-lobed; florets 3-25+; pistillate heads with egg-shaped involucre, about 1/6 inch long, 1-flowered.

Fruits:

Bur-like, pyramidal, 1/5 to 1/3 inch long, hard, formed by floral bracts, glabrous or sparsely-hairy; beak 1/25 inch long, surrounded by 4-8 blunt spine-like projections; seed 1, small.

Habitat:

Moist disturbed sites, stream banks, roadside ditches, margins of ponds and lakes, old fields, waste areas, pastures.

Distribution:

Throughout Kansas

Origin:

Native

Reproduction:

By seeds

Forage Value:

Unpalatable for livestock, though horses will sometimes eat it. Deer eat the leaves and pheasants, quail, prairie chickens, and songbirds eat the fruits.

Uses:

Native Americans rubbed crushed leaves on insect bites and steeped the leaves to make a tea taken for fevers and pneumonia and used as a wash for hives. The root was chewed to alleviate fear at night. Stem fibers were used as thread. Giant ragweed provides wildlife cover.

Comments:

Giant ragweed is highly variable. It is wind pollinated and is a major cause of allergy symptoms in the fall. It will form colonies in disturbed areas. Can be a problem weed in cultivated fields.

Giant ragweed inflorescence