Calamites, originally, a stem fragment of a fossil plant prominent during the coal age, the Carboniferous Period (from 286 million to 360 genus of tree-sized, spore-bearing plants that lived during the Carboniferous and Permian periods (about 360 to 250 million years ago). As such, it was termed a form genus. Later, the connotation was broadened to include an idealized treelike plant, and it became a full genus designation. Furthermore, the term calamite is used for any member of the family to which the original Calamites was assigned; the Calamitaceae, order Calamitales, class Sphenopsida. Calamites and other treelike plants of the coal age constitute the coal that provides a source of energy today. Calamites had a well-defined node-internode architecture similar to modern horsetails, and its branches and leaves emerged in whorls from these nodes. Its upright stems were woody and connected by an underground runner; however, the central part of the stem was hollow, and fossils of Calamites are commonly preserved as casts of this hollow central portion. Calamites grew to 20 metres (about 66 feet) tall, standing mostly along the sandy banks of rivers, and had the ability to sprout vigorously from underground rhizomes when the upper portions of the plant were damaged. The remains of Calamites and other treelike plants from the Carboniferous Period were transformed into the coal used as a source of energy today. A virtually identical plant from the Triassic Period (about 250 to 200 million years ago) is called Neocalamites.