Wander across a Missouri prairie or glade, or even along a roadside with wet ditches, and chances are you'll spot prairie dock, compass plant, cup plant, rosinweed or starry rosinweed. Each of these Missouri plants is an individual in its own right, but all are related species in the genus Silphium.
These tall, sturdy members of the sunflower family all are perennial plants with sandpaperlike leaves. All have sunflowery blossoms that range from the size of a silver dollar to a saucer. But like many relatives, they have their differences. They claim different territories, and each has developed its own ways to survive.
Silphium is the ancient name of a resinous plant. It was given to this group of plants because of their pine-scented, resinous sap. On a summer hike in most Missouri prairies, you will likely come across compass plant stalks or a clump of rosinweed and find small globs of sap exuding from the stems.
As John Madson writes in Where the Sky Began, "[Pioneers] found that [the compass plant] produced a pretty good brand of native chewing gum. Drops of clear sap exude from the upper third of the stem and solidify with exposure.
It has an odd, pine-resin taste that's pleasant enough, but it must be firmed up before it's chewed. A couple of summers ago I tried some of this sap while it was still liquid. It's surely the stickiest stuff in all creation, and I literally had to clean it from my teeth with lighter fluid."
Cattle, however, seem to have no problem with the sap. As Aldo Leopold writes in A Sand County Almanac, "I once saw a farmer turn his cows into a virgin prairie meadow previously used only sporadically for mowing wild hay. The cows cropped the Silphium to the ground before any other plant was visibly eaten at all. One can imagine that the buffalo once had the same preference for Silphium."
The resinous sap and sandpaperlike leaves of Silphium species may deter some insects or other grazers. The tough leaves also slow transpiration, helping the plants conserve water.
Silphium species have other survival strategies. Aldo Leopold's admiration for the tenacity of compass plant is apparent in his "Prairie Birthday" essay in A Sand County Almanac:
"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, that 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 drouths." In fact, the roots of compass plant, rosinweed, starry rosinweed and prairie dock can attain depths of 10 to 15 feet.
Perhaps no other plants in Missouri are as easily recognizable and as widespread as Silphium species. And, with their preference for various natural communities, their presence gives a dramatic flair to our prairies, glades, wetlands and ditches.
We often remember individual trees we have seen along the road or on a favorite hike, and even revisit them year after year. Plants like the species of Silphium are perhaps even more impressive than trees. Left undisturbed, they can attain a height of 10 feet every year, die back and begin the growth cycle again, for years and years.
Prairie dock - Silphium terebinthinaceum
"With turpentine," is the translation for the Greek name, terebinthinaceum, given to prairie dock for its resinous sap. A common sight on Ozark limestone glades, bald knobs and some prairies, the large toothed leaves of prairie dock stand upright like giant spade-shaped pieces of green sandpaper.
Prairie dock flowers are as striking as the leaves. The bright yellow flowers top slender stalks that rise up to 10 feet above the leaves in mid to late summer. Strangely enough, prairie dock prefers prairies in Iowa, Illinois and Indiana, but in Missouri it favors glades and rocky roadsides.
Cup plant or carpenter's weed - Silphium perfoliatum
Cup plant leaves are paired on opposite sides of the stem, and the pairs are arranged at right angles to each other along the stem. The scientific name of cup plant, perfoliatum, means "through the leaf," referring to the stem that appears to pierce the leaves. These stem-enclasping leaves are described as perfoliate and form a cup that can hold water. Whether this ability is advantageous to the plant is unknown, but small birds and insects have been known to drink from these cups.
As if the leaves weren't enough to make the plant striking, cup plant has square stems, which prompted the other common name of the plant, carpenter's weed. The plant grows most often in moist or wet ditches, swales or wetland or stream borders.
Compass plant - Silphium laciniatum
Like a ship's mast in a teeming sea of prairie plants, compass plant stalks-often 10 or more feet tall-are unmistakable prairie landmarks. As John Madson noted in Where the Sky Began, "Pioneers sometimes used compass-plant stalks to mark the edges of wagon routes over the wild prairies-tying scraps of cloth to the tall stems to indicate safe passage around boggy swales and sloughs."
Prairie birds, such as dickcissels, meadowlarks and Henslow's sparrows, like to perch on the tall stalks of compass plants and sing. In late summer and fall, goldfinches and other small birds eat compass plant seeds.
Compass plant leaves are like prairie dock leaves that someone went after with a pair of scissors. Latin for "deeply cut" or "lacerated," the species name, laciniatum, refers to the deeply lobed leaves. The basal leaves are what make this plant memorable: they align themselves in a north-south orientation. This internal compass allows the plant's broad leaves to have maximum exposure to the morning and evening sun and minimal exposure to the hot, drying, direct noon sun.
Rosinweed - Silphium integrifolium
A bit more understated than other Silphium species, rosinweed leaves are about 3 inches long and arranged opposite one another along a purplish green stem. The species name, integrifolium, is Latin for "entire-leaved," referring to the smooth, toothless leaf edges. Rosinweed is a prairie resident that can reach 7 feet tall and often grows in colonies or clusters. Like other Silphium species, rosinweed produces resinous sap and blooms in mid to late summer.
Starry rosinweed - Silphium asteriscus
Greek for "little star," asteriscus most likely refers to this plant's starlike flowers. Known from only 18 southern Missouri counties, starry rosinweed grows on sandy ground, open rocky woods and glades. While it is similar in size and growth habit to rosinweed, starry rosinweed has alternate, rather than opposite, leaves and has fine hairs covering the stems and leaves.
The Missouri clan of Silphium is small compared to all the members in North America: there are 23 species that range from Florida northwest to the Dakotas and southwest to Texas. Our Silphium species are widespread in Missouri, as well as throughout the Midwest and in southern states.
The genus Silphium is classified by botanists as belonging to the Asteraceae, or sunflower, family.
Including Silphium, the Asteraceae family contains 1,314 genera worldwide and 88 in Missouri. Familiar Asteraceae plants include sunflowers, chrysanthemums, daisies, coneflowers and blazing star. Like these plants, Silphium shares the characteristic of having many flowers in a single head: a sunflower or Silphium blossom is actually composed of numerous individual flowers.
Asteraceae flowers can be bisexual, (containing both male and female reproductive organs) or unisexual (individual flowers with either male or female parts).
What sets Silphium apart from other members of the Asteraceae family is that its ray flowers-the individual flowers around the rim of the flower head with one large yellow petal each-are female, whereas the flowers in the center are male. So seeds of Silphium are produced only around the edge of the flower heads.
In addition, the seeds of Silphium are flattened with wings to help them disperse, unlike many other plants in the Asteraceae family.