Calamites sp. is the pith cast of the stem of an extinct horsetail. Scouring rushes (Equisetum spp.) are modern representatives of this group.
These horsetails (Sphenopsida) were arborescent (tree-like) and grew to a height of up to 10 meters (31 feet).
Whorls of leaves, such as Asterophyllites, would have been present on these types of plants.