The oldest public wildflower garden in the United States
Prairie Dock (Prairie Rosinweed)
Silphium terebinthinaceum Jacq.
Late Summer to Autumn Flowering
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".
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. The styles of both florets are visible but those of the disc florets are non-functional.
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.
Below: The height of Prairie Dock can be seen in this view of a hillside in the Upland Garden at Eloise Butler.
Notes: Prairie Dock first entered the Garden in 1923 when Eloise Butler obtained plants from Lake Geneva Wisconsin. She added others in 1932 from Barksdale Wisconsin. Martha Crone added plants in 1939 and then seeds in 1942 and more plants in 1951 and 1955 when she developed the upland part of the Garden. Ken Avery planted it in 1963 and 1970. Although some books list it as found in Minnesota, it has never been surveyed in the wild and is considered not native to Minnesota, although it will grow well here in the right conditions. 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.
A Story: In 1932 Eloise Butler wrote the following about her experiences with Prairie Dock:
"Are you all familiar with Prairie Dock, Silphium terebinthinaceum, belonging to the same genus as the famous Compass Plant, S. laciniatum? A single specimen was given me nine years ago and I planted it near my office. Every season it sent up its large green banners, but nary a flower. I hesitated to change the plant to another situation because of its large root and lest I might lose it altogether. So this last spring I gave it a ‘good talking to’ and bought half a dozen more Prairie Dock and planted them elsewhere. To my astonishment the obstinate specimen sent up at once the tall stalk that burgeoned out into a number of sizable yellow flowers! I have had somewhat similar experiences. Does it mean that plants are sentient beings?" From her unpublished work Annals of the Wildlife Reserve.
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.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wildflower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofeloisebutler.org"