Equisetaceae, sometimes called the horsetail family, is the only extant family of the order
Equisetales, with one
surviving genus, Equisetum, which comprises about twenty species.
Evolution and systematics
Equisetaceae is the only surviving family of the Equisetales, a group with many fossils of large
tree-like plants that possessed ribbed stems similar to modern horsetails.
Pseudobornia
is the oldest known relative of
Equisetum; it grew in the late Devonian, about 375
million years ago and is assigned to its own order.