Equisetum (a modern genus of horsetail) is a primitive, spore-bearing plant (a sphenopsid) with rhizomes. Its side branches are arranged in rings along the hollow stem. Other genera of horsetail were common during the Mesozoic Era, like Neocalamites, Calamites etc. Horsetails date from the Devonian period 408-360 million years ago, but are still around today and are invasive weeds.
Equisetum is a genus of vascular plants that reproduce by spores rather than seeds. The genus includes 15 species, commonly known as horsetails and scouring rushes. Equisetum is the only one in the family Equisetaceae, which in turn is the only family in the order Equisetales and the class Equisetopsida.