Calamites

Calamites, a genus of fossil Equisetaceae or horse-tails, found in the Carboniferous and Permian formations, generally merely as casts of the pith-cavity of a stem. Some species seem to have had a smooth surface and thick rind; others, to have had thinner rind and fluted internodes, as in the living Equisetum. They had solid nodes and apparently whorls of simple leaves; but their sporangia are not accurately known. The stems of Calamites may be prostrate or erect, and sometimes exceed 20 feet in height.