Prairie Dock (Prairie Rosinweed)

Silphium terebinthinaceum

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Photo of a prairie dock flowerhead
Of Missouri's six species of rosinweeds, prairie dock is identified by its large, basal, unlobed leaves; there are only small, bractlike leaves on the stem.
Family

Asteraceae (daisies, sunflowers)

Description

Prairie dock is 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, prairie dock, 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.

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Photo of prairie dock leaves in basal cluster
Prairie Dock Leaves
Prairie dock's basal cluster of large, unlobed leaves, combined with its very tall, leafless stalks, helps ID this plant.

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Photo of a prairie dock flowerhead, viewed from the side
Prairie Dock (Prairie Rosinweed)
Prairie dock is common in areas with limestone or dolomite rock.

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Photo of several prairie dock plants showing large basal leaves.
Prairie Dock (Leaves)
Of Missouri’s six rosinweeds, prairie dock is identified by its large, leathery, unlobed leaves, which are nearly all in a basal whorl.

prairie_dock_flower_7-17-14.jpg

Photo of a prairie dock flowerhead.
Prairie Dock (Flowerhead)
Prairie dock, like other Missouri rosinweeds, has yellow, sunflower-like flowerheads.

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Prairie dock
Prairie dock
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.

image of Prairie Dock (Prairie Rosinweed)
Distribution in Missouri

Scattered, mostly in the Ozark and Ozark Border Divisions, in central and northeastern Missouri.

Status

It’s not an accident that rosinweeds are in their own genus, Silphium, and not in the genus Helianthus (sunflowers). Yet some of them look much alike. How can you tell the difference? The disk florets in rosinweeds are essentially staminate (male) and therefore don’t create seeds, just pollen; but the disk florets in sunflowers, as most of us know, create seeds. The petal-like ray florets in rosinweeds are pistillate (female) and turn into seeds, while those in sunflowers are sterile.

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.