Horsetail

Equisetum
Vegetative stem of Equisetum telmateia with a whorl (at each node) of branches and dark-tipped leaves Early Jurassic to present
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Class:	Equisetopsida
Order:	Equisetales
Family:	Equisetaceae
Genus:	Equisetum

The horsetails are a class in the Pteridophyta (ferns). They were one of the most important plant groups in the Palaeozoic era.

For over 100 million years they were varied, and dominated the understorey of late Paleozoic forests. They are seen in the coal measures of the Carboniferous period, and some were trees reaching up 30 metres.^[1] The group is now almost extinct, but one genus survives. They are vascular plants that reproduce by spores and not by seeds. The name horsetail came because the branched species somewhat look like a horse's tail.

1. ↑ Pryer K.M. et al 2004. Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences. American Journal of Botany 91: 1582-1598 (available online Archived 2007-09-26 at the Wayback Machine; pdf file)