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Prairie Dock (Prairie Rosinweed)

Prairie Dock (Flowerhead)

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Prairie Dock (Leaves)

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Silphium terebinthinaceum
Family: 
Asteraceae (daisies, sunflowers)
Description: 

A tall perennial herb with woody taproots, the flower stalk very slender, with reduced stem leaves. Flowerheads one to few in an open inflorescence on a long stem; yellow, with 15–21 rays. Blooms July–October. Leaves almost all basal, very large, to 16 inches long, heart- or spade-shaped, with coarse teeth, on a long petiole, thick, leathery, and rough like sandpaper. The leaves develop all summer and are present at flowering time. The flower stalk rises in early fall. The species name means “with turpentine” and refers to the rosin, which gives this plant a pleasant scent.

Similar species: There are 6 Silphium species recorded for Missouri. Of these, starry rosinweed (S. asteriscus), rosinweed (S. integrifolium), compass plant (S. laciniatum), and cup plant (S. perfoliatum) are relatively common. Prairie dock is identified by its large, basal, unlobed leaves with only small, bractlike leaves on the stem.

Size: 
Height: to 10 feet.
Habitat and conservation: 
Occurs in glades, upland or rocky prairies, tops of bluffs, savannas, openings of dry upland forests, and rarely banks of streams; also old fields, railroads, and roadsides. Look for it in areas with limestone or dolomite rock. Like its relative compass plant, the leaves of prairie dock often are oriented north and south, maximizing morning and afternoon sun for photosynthesis and minimizing water loss from midday heat.
Distribution in Missouri: 
Scattered, mostly in the Ozark and Ozark Border Divisions, in central and northeastern Missouri.
Human connections: 
Although the resinous sap has a turpentine-like odor, grazing animals find this plant palatable. As with other rosinweeds, the gummy sap that it exudes was used by Native Americans and pioneers as a kind of chewing gum. It is a tough, showy native flower for the back of a garden.
Ecosystem connections: 
Birds, including goldfinches, eat the seeds. Many insects visit and pollinate the flowers. If you inspect a rosinweed plant closely, you will find that many insects live, hunt, eat, and mate among the leaves and flowers. Also, the larvae of some wasps grow with in the stems, forming galls.
Shortened URL
http://mdc.mo.gov/node/28697