Conceptual illustration of a Carboniferous-Permian coastal river delta wetland environment featuring Calamites, a genus of tree-sized, spore-bearing plants that lived during the Carboniferous and Permian periods about 360 to 250 million years ago. Calamites grew to 20 metres tall, standing mostly along the sandy banks of rivers. The remains of Calamites and other treelike plants from the Carboniferous Period were transformed into coal. The best-known Pennsylvanian tropical ecosystems were the coal swamp forests that formed from widespread peatlands.