Equisetum

The genus Equisetum (horsetails or scouring rush) occurs worldwide (except for Australia and New Zealand) and consists of 16 living species, plus 19 naturally occuring hybrids. They are to be found in nearly every state in the USA, with nine species plus one hybrid (Equisetum ×ferrissi) native to California.

Equisetum grow in or near wet areas, often along rivers and in wetlands, primarily in temperate climates. They vary in height from a few centimeters (about one inch) to 'giants' reaching six meters (20 feet) tall. The giant species, Equisetum giganteum and Equisetum myriochaetum, are endemic to a region covering central Mexico to central Argentina and Chile.

Worldwide distribution of 'giant' Equisetum species:

Nearly all species require plenty of light, are intolerant of shade, and will grow in full sun. They are suited to growing in wet soil or standing water, and should never be allowed to dry out. A few species are deciduous.

Some species (i.e. Equisetum arvense and Equisetum hyemale) are aggressive spreaders and can become invasive. They may be considered as weeds in some areas (for instance Equisetum are prohibited in the State of Victoria, Australia).

Equisetum is the only surviving genus of the Equisetales, an ancient group of plants which can be traced back to the Carboniferous Period (299 to 359 million years ago). The fossil record shows that the now extinct genus Calamites once grew to the size of modern trees, reaching 20 meters (65 feet) tall, and are a significant component of the Carboniferous coal deposits worldwide.

Click here for Equisetum in the the Encyclopedia of Life.

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