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
ROSINWEEDS OF THE PRAIRIES
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.
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
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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Update: June 2012