Compass Plant is a native erect perennial long-lived prairie plant, growing on stout leafy stems 6 to 8 feet in height.
Basal leaves are stalked and very deeply pinnately-divided, as much as 24 inches long and half as wide. Lobe tips are pointed. Stem leaves are alternate and become much smaller and leaves near the top of the stem may not be divided at all. The most upper leaves may be stalkless. All leaves are hairy.
The floral array consists of several flowering heads in an upright narrow cluster atop the stem.
Flowers are stalked and when open are 2-1/2 to 4 inches wide. The outer ray florets are yellow, fertile, and usually with 27 to 38 rays with the single style at the base. These surround a group of 100+ central disc florets the have yellow tubular corollas and five stamens, but are functionally staminate only (not fertile). The outer flower head has 2 to 3 series of green phyllaries (bracts) with the inner series appressed to the head and the outer series reflexed. In the Silphiums, each ray floret is subtended by a phyllary. These, like the flower stalk have hairy outer surfaces, sometime with glandular hairs.
Seed: Fertile ray florets produce a flattened large dry seed (a cypsela), 10–18 × 6–12 mm, without fluffy pappus, but light enough for some wind distribution. Silphium seeds require 60 days of cold stratification for germination.
Varieties: The older literature usually lists two varieties: var. laciniatum, which is said to be native to Minnesota and the most of the great plains and eastward north of Tennessee to the Appalachians, and var. robinsonii, which is native to the southern plains south of Oklahoma and east to Tennessee and Mississippi. HOWEVER, currently Flora of North America and the Minnesota authorities at the U of M Herbarium consolidate the varieties.
Habitat: Compass Plant needs full sun in sandy to loamy soils, with mesic to dry moisture conditions. It grows from a taproot which becomes large and deep with age, making for drought resistance.
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 laciniatum, means 'slashed' or 'torn into divisions' and applies to the deeply divided leaves. The common name comes from the tendency of lower leaves to be somewhat upright with the edges aligned in a north-south direction. Compass Plant is sometimes listed in references as Rosinweed, but that name should be reserved for a different species - S. integrifolium. The author name for the plant classification - 'L.' is for Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: Compass Plant is one of several tall composite plants that grow in Eloise Butler. For more detail on this plant and the other Silphiums in the Garden, see our article "The Four Silphiums".
Above: Compass Plant. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: 1st photo - the outer ray florets are fertile while the inner disc florets are not. 2nd photo - The phyllaries are in several series, each subtending a ray flower. Outer surfaces have hair.
Below: 1st photo - Flower heads are 2-1/2 to 4 inches wide. 2nd photo - Whitish stem hair. 3rd photo - Very large basal leaves.
Notes: Eloise Butler first recorded planting Compass Plant in 1913 - first on July 12 with a plant transplanted from the "Beltline Bridge" (the "Beltline" is current state highway 100 in Minneapolis) and then with seeds on Sept. 10. More were added in 1915. Martha Crone planted it in 1948 and sowed seeds in 1953. It was listed on her 1951 inventory of plants in the Garden at that time. The plant is native to Minnesota in the SE quarter from Ramsey county south and also across the southern tier of counties to the Dakota border. Compass Plant is one of two Silphiums native to Minnesota, the other is Cup Plant, S. perfoliatum. In North America, Compass Plant, Silphium laciniatum is found from the Central Plains eastward to New York, Pennsylvania and Virginia, absent in the Gulf Coast area in the U.S.; Known only in Ontario in Canada.
Eloise Butler wrote of this plant: "The interesting Rosin, or Compass Plant of the prairie (Silphium laciniatum L.) is of the same genus as the cup plant. Its leaves are cut edgewise and point due north and south. Persons lost on a trackless, uninhabited prairie might find their bearings by this vegetable compass. An army officer stationed on the western plains, the first observer of the plant, thought the leaves must have the properties of the magnetic needle. Failing to prove this theory by experiments, he forwarded specimens of the Silphium to Dr. Asa Gray, the American Darwin, who suggested that the peculiar position of the leaves was for the purpose of avoiding the direct rays of the sun in order to check too great a loss of water by transpiration. Since that time “polarity” has been observed in the leaves of many other plants growing in drought regions or in exposed situations, as the eucalyptus trees of Australia. Such trees, of course, afford no shade. The habit may be noted in the roadside weed prickly lettuce, and in some degree even in the garden lettuce." Published in the Minneapolis Sunday Tribune, July, 16, 1911. (Read article)
Aldo Leopold wrote: "Silphium first became a personality to me when I tried to dig one up to move to my farm. It was like digging an oak sapling. After half an hour of hot grimy labor the root was still enlarging, like a great vertical sweet-potato. As far as I know, the Silphium root went clear through to bedrock. I got no Silphium, but I learned by what elaborate underground stratagems it contrives to weather the prairie droughts." (Ref.#18a ).
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"