Prairie Dock is the tallest composite in the Upland Garden, growing from 4 to 10 feet high with numerous flower heads. It is perennial and late summer flowering.

Stems are smooth, bare, (no leaves) with branching in the floral array, green, but turn reddish in autumn.

Leaves are large, triangular shaped, basal only, stalked, un-lobed, with large pointed teeth, rough with a heart shape base. They can be up to 18 inches long and 12 inches wide. Young leaves have fine hair on the leaf and the stalk.

The floral array is a large open spreading branched panicle.

Flowers: The yellow composite flower heads are 2 - 3 1/2 inches wide and on long stalks. They have 17 - 29 fertile pistillate yellow ray florets that have pointed tips on the rays; these surround a central disc of 1/2 - 1 1/2 inches width, composed of over 120 functionally staminate sterile tubular disc florets. The disc florets have a deep-yellow colored 5-lobed corolla with spreading tips at the apex. The disc floret tube is shorter than the corolla. Five stamens tightly surround a single unbranched style, which is exserted when the floret opens, but is non-functional. The phyllaries that surround the outside of the flower head (bracts) are in 2 to 3 series, broad, smooth, not spreading, rounded (obtuse) at the top. In the Silphiums, each ray floret is generally subtended by a phyllary.

Seed is a dry narrowly winged cypsela, 7–13 × 4–10 mm, without pappus. Seeds are distributed by wind shaking the stem. Seeds require 60 days of cold stratification for germination.

Varieties: Two varieties are recognized: var pinnatifidum where the leaves are pinnately lobed and var. terebinthinaceum where the leaves are not lobed. The latter is the variety shown here.

Habitat: Prairie Dock grows best in full to partial sun with soils that are well drained and wet-mesic to dry mesic. It makes a deep taproot. It is usually not a plant for the small home garden, but given the space, it is an impressive plant and pollinator friendly.

Names: The genus name, Silphium, is from the Greek word silphion, which was a plant of North Africa, unidentified today, that was used as a seasoning, perfume, aphrodisiac, and medicine, and contraceptive. The sap was odiferous and delicious. It only grew in the Cyrenaica, and was thought to be extinct already by the time of Nero. Images of the the plant appeared on ancient Greek coins of the city of Cyrene. Silphium is used today for a group of plants with resinous juice. The species name, terebinthinaceum, means "like turpentine" which may refer to the odor of the resinous juice. The name terebinthinaceum is derived from the terebinth tree of the Mediterranean region that is a source of turpentine. The author name for the plant classification, published in 1770 - ‘Jacq.’ is for Nikolaus Joseph von Jacquin (1727-1817), Dutch botanist who became Professor of Botany and Chemistry at the University of Vienna where he was also director of the botanical gardens.

Comparisons: For more detail on this plant and the other three Silphiums in Eloise Butler, see our article "The Four Silphiums".