Equisetopsida

Equisetopsida, (division Pteridophyta), class of primitive spore-bearing vascular plants. Most members of the group are extinct and known only from their fossilized remains. The sole living genus, Equisetum, order Equisetales, is made up of 15 species of very ancient herbaceous plants, the horsetails and scouring rushes. Extinct members of the division, some of which have been traced back as far as the Devonian Period (416 to 359 million years ago), include many herbaceous Equisetales, shrubby Hyeniales, vinelike Sphenophyllales, and trees of the family Calamitaceae.