The webmaster was surprised to find several colonies of this wetland plant growing on the gravelly embankment of a railroad. For some reason, Horsetails often do this, even though this type of habitat is supposed to be too dry for them. Water Horsetail is a rather slender and medium-sized Equisetum sp. that produces small whorls of branchlets in the upper half of its stems. It is smaller than Equisetum hyemale var. affine (Scouring Rush), but larger than Equisetum arvense (Field Horsetail). Field Horsetail also produces whorls of branchlets along its stems, but its branchlets are more abundant and they eventually become almost as long as the central stems. The branchlets of Water Horsetail are less abundant and they are always much shorter than the central stems. Water Horsetail resembles Equisetum palustre (Marsh Horsetail), Equisetum pratense (Meadow Horsetail) and Equisetum sylvaticum (Woodland Horsetail), but its stems are more hollow. The interior cavity of these latter species spans less than 50% of the diameter of their stems.