The plants that became Pennsylvanian coal came in a wide variety of sizes and shapes. One that Mark Twain mentioned in the quote yesterday, calamites, was a common swamp plant similar to modern horsetail rushes – but much larger. Modern rushes are maybe a foot tall, but Pennsylvanian calamites grew to 30 meters high, or more than 100 feet. They were definitely trees, at least in terms of size.
Calamites trunks were thick segmented stems with ribbed surfaces, sort of like bamboo, and the stems were hollow, like bamboo, so when they died and fell, often they would split open and some of the most common fossils are internal casts of the hollow stem that had filled with sediment after death.
|Annularia (Calamites leaves)|
As a group, calamites began during the Mississippian but proliferated during the Pennsylvanian at least in the equatorial regions, which included much of North America and Eurasia, which were attached to each other. They declined and became extinct fairly soon after the end of the Pennsylvanian, during the early Permian Period.
—Richard I. Gibson
Annularia photo by Woudloper, Collection of the Universiteit Utrecht, public domain
Drawings from old texts, public domain