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Native Wildflowers of the North Dakota Grasslands

JPG -- species photo

Western Ragweed (Ambrosia psilostachya)


Found throughout North Dakota, western ragweed occurs naturally from the Appalachian region to the Rocky Mountains, and is adventive in Europe and elsewhere.

Western ragweed grows nearly four feet tall in some places, but most North Dakota plants are about half that height. Plants are perennial from creeping rootstalks and thus form clumps of many stems. Leaves are about 2-3 inches long, opposite, and deeply cut into narrow lobes that are again lobed. About 5-10 tiny yellow flowers form heads about one eighth inch across; these are in turn grouped into spikes about 1-2 inches long that arise from the upper half of the plant and overtop the leaves. Fruits are tiny achenes that fall at maturity enclosed in two bracts.

Look for western ragweed in late August in both native prairie and waste places. Grazing does not seem to influence the abundance of this plant. Western ragweed was used in teas for various medicinal purposes by several Amerindian tribes. The Kiowa rolled the plant up with different sages for use in sweathouses. Ragweed pollen is a notorious hazard to hay-fever sufferers.

The ragweeds are members of the large and economically important sunflower family (Asteraceae) which has about 15,000 species worldwide and 200 in North Dakota. Ambrosia is a Greek name of several plants, as well as the food of the gods, an inappropriate name for these bitter plants. There are about 15 species of Ambrosia; most are native to North America. Four species occur in North Dakota. Psilostachya means "naked-spiked" in botanical Latin.

Western ragweed was described for science by Agustin Pyramus de Candolle (1778-1841), Swiss botanist and founder of the Prodromus, a fundamental work in the development of modern taxonomy. Never completed, writing began in 1816 and was continued by the de Candolle family for 102 years! Remarkably, the Prodromus is still the only systematic treatment available for some groups of plants.


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