Scientific Name: Equisetopsida
Status: Extant (alive today)
Oldest fossil anywhere: Devonian of Spitsbergen (Norway) and Alaska (about 375 million years old)
Oklahoma fossil record: Macrofossils have been found in Oklahoma rocks deposited during the Pennsylvanian and Permian Periods.
Horsetails grow along rivers and streams; most are less than 5 feet (1.5 meters) tall, but the largest species may each about 20 feet (7 meters). Extinct horsetails reached 100 feet tall (30 meters).
Horsetails do not have seeds; they have tiny leaves and roots, vascular tissue and use spores to reproduce. One group of extinct horsetails known as Calamites produced wood (secondary xylem) which they evolved independently of Archaeoteridales and seed plants.
Recently, genetic studies have demonstrated that one group of ferns, once considered a distinct group, are actually related to Horsetails. Horsetails and ferns and are grouped together in Monilophyta.