Equisetopsida, or Sphenopsida, is a class of plants with a fossil record going back to the Devonian. They are commonly known as horsetails. Living species typically grow in wet areas, with needle-like leaves radiating at regular intervals from a single vertical stem.

The Equisetopsida were formerly regarded as a separate division of spore plants and also called Equisetophyta, Arthrophyta or Sphenophyta; today they have been recognized as rather close relatives of the typical ferns (Pteridopsida) and form a specialized lineage of the Pteridophyta.

Read more about Equisetopsida:  Morphology, Fossil Record, Systematics