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) 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 flower heads are 2 - 3 1/2 inches wide and on long stalks. They have 17 - 29 fertile pistillate ray florets that have pointed tips; these surround a central disc of 1/2 - 1 1/2 inches width, composed of over 120 functionally staminate sterile disc florets. The disc florets have 5 stamens, a deep-yellow color 5-lobed corolla with spreading tips at the apex. 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 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 said to have resinous juice that was medicinally sought after. This 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 author name for the plant classification - ‘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".
Above: The floral array is a large open spreading branched panicle. The yellow flower heads are 2 - 3 1/2 inches wide and on long stalks. The phyllaries (3rd photo) are wide, erect, smooth, with rounded tips.
Below: 1st photo - Emerging leaves have hairy undersides and stalks. 2nd photo - The pistillate ray florets are fertile and surround the sterile disc florets.
Below: Leaves are basal on long stalks. Mature leaves have heart-shaped bases, pointed large teeth. 2nd photo - this gives you a perspective of the plant's height.
Notes: Prairie Dock was listed on Martha Crone's 1951 inventory of plants in the Garden at that time. She was the first to plant it, first with plants in 1939 and then seeds in 1942 and more plants in 1951 and 1955. Ken Avery planted it in 1963 and 1970. It in not native to Minnesota. It is a plant of the east central United States, not found further west than Wisconsin, Iowa, Missouri and Arkansas. In Canada it is known only from Ontario.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"