Forest Preserve District of Cook County, Illinois
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Rosinweeds of the Prairies
Nature Bulletin No. 198-A   September 18, 1965
Forest Preserve District of Cook County
Seymour Simon, President
Roland F. Eisenbeis, Supt. of Conservation

More than half of Illinois, the Prairie State, was originally prairie -- largely the Tall Grass Prairie characteristic of the climatic zone where the annual rainfall averages 35 inches or more, dominated by such grasses as the big bluestem and coarse slough grass which grew 6 to 8 or more feet tall, so thickly that most other plants were excluded. The ridges and uplands, however, were characterized by the little bluestem and similar grasses growing from 2 to 4 feet tall.

Plants are crowded in a prairie. There is severe competition for sunlight, food and moisture. The early spring plants are mostly small and low, growing rapidly to mature before they are overshadowed by the grasses. By midsummer, taller plants that bloomed in late spring are nearly hidden. But the late summer and autumn blooming plants continue to grow until most of them stand far above the grasses.

From mid-July until October is the season of purple and gold. Many species of goldenrod bloom, sometimes in great masses. The yellow and gold of the sunflower and rough oxeye punctuate broad bands of lavender and purple created by the candle-like heads of the blazing stars. In August, the brilliant purple flowers of the ironweed appear and, until late fall, numerous asters bloom in colors varying from white or lavender to blue or rich purple. Meantime, the prairie grasses slowly take on the red and bronze and golden tints of autumn. Towering above them all, stand the yellow flowers of two rosinweeds: the Compass Plant and the Prairie Dock.

The compass plant gets its name from the fact that each leaf, especially the large erect ones at its base, tends to twist into a vertical plane with its edges pointing north and south, so that both surfaces of these stiff rough deeply-divided leaves share the sunlight equally. The stalk, which grows from 6 to 12 feet high, is stout, rough, covered with stiff hairs, and bears several or many heads of big yellow flowers which are sometimes 5 inches broad. It exudes white sticky aromatic blobs of resinous juice when cut or broken, often used as chewing gum by children.

The prairie dock seems to prefer dry prairies and warm gentle slopes. It is striking because of its very large rigid leaves, very rough on the underside, heart-shaped, with spiny teeth along the edges. Commonly a foot long and 6 inches wide, we measured several that were 18 inches long and 12 inches wide. In autumn they turn dark brown and curl stiffly in decorative shapes. The stalk grows from 4 to 10 feet tall, smooth and leafless except at the base. It usually branches near the top and bears many yellow flowers 2 or 3 inches broad.

The Entire-leaved Rosinweed is another common prairie plant, with thick rigid leaves on a stout stem that grows 2 to 5 feet tall, branching near the top and bearing numerous yellow flowers. The Cup Plant grows in low moist places. Its stout square stem bears big coarsely- toothed leaves in pairs, the upper pairs grown together to form cups often partly filled with water and drowned insects.

In the prairie, characterized by successive layers of bloom above the ground, we find successive layers of roots in the soil. A few plants send their roots down not more than 18 inches; some reach a depth of 4 or 5 feet; but about 65 percent penetrate much deeper: sometimes 20 feet or more. Among these we find the big tough taproots of the rosinweeds, which go down and down and down. Actually, the bulk of the prairie is not above the ground but is below the surface.

This fact made possible the Corn Belt the breadbasket of our nation.

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