Illinois State Museum

check Check the Clue - A Tree or Not a Tree?

Pennsylvanian Period Trees
Illinois State Museum Exhibit

The rain forests that grew in Illinois during the Pennsylvanian Period were dominated by giant lycopods. At 40 meters (about 130 ft.) tall, with trunks several meters (7–10 ft.) in diameter, they were the redwoods of their day. But, were they trees?

Compare Past and Present.
Lycopods were tree-like in many ways. They were tall, with trunks, branches, leaves, and roots. However, their stems were made of large, thin-walled cells. This characteristic shows that they grew rapidly, probably achieving maximum size in only a few years. Modern trees have woody stems and distinct annual growth rings.

Although we call them trees, lycopods were actually more like weeds than present-day trees. Tree-sized lycopods were distant relatives of tiny club mosses. They became extinct in the Permian Period (250 million years ago), when sea levels fell and worldwide climate became much drier.

Bark Layers
To the left are fossils of bark from lycopods. Each fossil was given a different name. It took researchers many years to realize that they came from just two plant genera - Lipodendron and Sigillaria. The trunks of each plant were layered and each layer had a different pattern. As the lycopod's leaves dropped off, they left distinctive scars on the bark - spirally arranged, diamond-shaped scars in Lepidodendron and vertical rows of geometric scars in Sigillaria.

Present-day Relatives
Modern lycopods, called ground pines or club mosses, resemble small evergreens or mosses and are only a few centimeters (1–5 in.) tall.