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Wisconsin Plant of the Week

Silphium terebinthinaceum Jacq.

Asteraceae (Aster or Sunflower Family)

Common Name:

prairie dock

07/26/1999

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.

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.

  • 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)
     
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