Horsetail belongs to a primitive family of plants called the Equisetaceae. Horsetail has hardly changed since prehistoric times, although the plants were huge in comparison to now. The giant extinct horsetails (Calamites) were trees up to 1 meter in diameter and 30 meters in height. Their leaves – like those of extant horsetails – were arranged in spoke-like whorls at regular intervals along the jointed stems. Plants of this family – some of which have been traced back as far as the Devonian Period 400 to 350 million years ago – were part of the vegetation that formed our coal deposits.
