CHAPTER XXIV 
CALAMITES AND LYCOPODS 
I. THE HORSETAILS (EQUISETALES) 
EQUISETUM 
333. Habitat and Distribution. As the names of some 
of the various species indicate, representatives of the 
genus Equisetum occur in a rather large variety of habitats. 
Thus we have the swamp-equisetum (E. palustrej^eadow- 
equisetum (E. pratense), the field-equisetum (E. arvense), 
and so on. They are frequently found along railroad 
embankments in exposed situations, while other species 
occur only in shaded or very moist locations (Fig. 266). 
They are distributed throughout the northern hemi- 
sphere, but only one species has been reported from South 
America. Twenty species have been described from the 
temperate and tropical North America, but none has ever 
been found in Australia. Fossils of near relatives of the 
genus have been found in the rocks of previous geological 
ages, and some of the fossils in the coal-bearing rocks of 
the Carboniferous age are thought to belong to Equisetum 
itself. In temperate America the horsetails vary in height 
from only a few inches to several feet. One species (E. 
debile), found near Lahore, in India, attains a height of from 
loto 15 feet, needing the support of neighboring trees in 
order to stand erect, while E. giganteum, found from the 
West Indies to Chili, reaches a maximum height of 
368 
