SCOURING RUSHES (Plate 2)
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SCOURING RUSHES (Plate 2)
Although related to the small, inconspicuous horsetails of today, the ancient scouring rushes of the Pennsylvanian 13 Period grew to the size of trees and were among the most widely distributed plant groups.
Some of these plants attained heights of 40 feet or more, but the average was closer to 20 feet. The trunks were jointed and bore a whorl of branches at the joints (nodes). Their small leaves also grew in whorls at nodes along the smaller branches. Internodal regions were ribbed in the same manner as present day horsetails. Fossils of the trunks are assigned to the genus Calamites and quite commonly are preserved in sandstone and shale.
The leaf whorls are placed in the genus Annularia. One form commonly found in Illinois has long, pointed, needlelike leaves and is given the name Asterophyllites. Calamostachys, shown on plate 5, is one of the most common calamite cones.