Equisetum

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Equisetum

Vegetative stem of Equisetum telmateia with a whorl (at each node) of branches and dark-tipped leaves

Kingdom:	Plantae
Division:	Pteridophyta
Class:	Equisetopsida
Order:	Equisetales
Family:	Equisetaceae
Genus:	Equisetum

Species

See text

Equisetum (also horsetails or scouring rushes), is a genus of vascular plants that reproduce by spores and not by seeds. The genus includes 15 species.^[1]

The name horsetail, often used for the entire group, arose because the branched species somewhat resemble a horse's tail, the name Equisetum comes from the Latin equus, "horse", and seta, "bristle".^[2]

One can find horsetails on all continents except from Australasia and Antarctica. They are perennial plants, either herbaceous, they back in winter (most temperate species) or they are evergreen (some tropical species, and the temperate species Equisetum hyemale, E. scirpoides, E. variegatum and E. ramosissimum). They mostly grow 0.2-1.5 m tall, though E. telmateia can exceptionally reach 2.5 m, and the tropical American species E. giganteum 5 m, and E. myriochaetum 8 m.

In these plants the leaves are greatly reduced, in whorls of small, segments fused into nodal sheaths. The stems are green and photosynthetic, also distinctive in being hollow, jointed, and ridged (with (3-) 6-40 ridges). There may or may not be whorls of branches at the nodes; when present, these branches are identical to the main stem except smaller.

The superficially similar flowering plant, Mare's tail (Hippuris vulgaris), unrelated to the genus Equisetum, is occasionally misidentified and misnamed as a horsetail.

[change] References

↑ Equisetum is the only one in the family Equisetaceae, which in turn is the only family in the order Equisetales and the class Equisetopsida. This class is often placed as the sole member of the Division Equisetophyta (also called Arthrophyta in older works), though some recent molecular analyses place the genus within the ferns (Pteridophyta), related to Marattiales. Other classes and orders of Equisetophyta are known from the fossil record, where they were important members of the world flora during the Carboniferous period.
↑ Other names include candock (applied to branching species only), and scouring-rush (applied to the unbranched or sparsely branched species). The latter name refers to the plants' rush-like appearance; the stems were used for scouring cooking pots in the past (due to them being coated with abrasive silica).

Pryer, K. M., Schuettpelz, E., Wolf, P. G., Schneider, H., Smith, A. R., and Cranfill, R. (2004). Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences. American Journal of Botany 91: 1582-1598 (available online; pdf file).