Figure 21. Reconstruction of a tropical peat swamp of Middle Pennsylvanian age (about 300 million years ago). The taller plants (A) were tree lycopsids (Lepidophloios), some of which grew to heights of 80 to 100 ft. Today, the lycopsids are represented by lowly club mosses. Other plants include cordaites (B), which were seed plants with strap-shaped leaves that are now extinct; tree ferns (C), which still live in warm, damp areas; calamites (D), which is a tree-size scouring rush; and pteridosperms (E), which were seed plants with fernlike leaves that are now extinct. The tree-like scouring rushes, which reached heights of 30 to 50 ft, are represented today by plants that grow in damp, but not necessarily warm, areas usually to only a few feet in height. From an illustration by Alice Pricket in GSA Today (Gastaldo and others, 1996, fig. 1); Geological Society of America (GSA), copyright 1996, reproduced with permission of the GSA (Boulder, Colo.), whose permission is required for further use.