Prairie dock is one of four Silphiums in the northern Midwest prairies. Most are very large plants with large rough leaves that smell like turpentine when crushed and big flower heads.
Prairie Dock grows in mesic calcareous prairies and fens in deep soil. Its large woody taproot sends up new shoots so that the plant can persist even after heavy grazing or disturbance.
Origin of the name: Silphium, Greek name for another resin-producing plant; terebinthinaceum, L. terebinthus, turpentine
Range: S. Ontario to MN, s. to GA and MS
WI Range: SE Wisconsin, n to Brown, e to Juneau and Green Counties
Common associates: Big bluestem, bush clover, gray-headed coneflower in mesic prairies; cladium, grass-of-parnassus, Ohio goldenrod in fens.
Wetland Indicator Status: FACU
Coefficient of Conservatism: C = 5 (S&W), C = 6 (MI)
The very large basal
leaves, up to 3 dm broad and vertical on long petioles, make the plant easily recognizable from a distance. The flower heads grow at the top of smooth stems up to 3 m tall with very small leaves.
It blooms from July through September with yellow flowers to 5 cm across.
Silphiums are distinguished from the sunflowers (Helianthus) in that Silphium seeds form in a ring around the disc, since only
the ray flowers are fertile (see insert). In the sunflowers, the seeds cover the whole disc.