A Handbook of Systematic Botany

The botanical account attributes the stiffness of stems mainly to silica in the epidermal cell walls and to sclerenchymatous cells in the ridges. The leaves are described as arranged in whorls, with simple, undivided vegetative leaves possessing a single nerve and united into toothed sheaths. The fertile leaves are free and shieldlike, each with a short stalk usually bearing a hexagonal plate, and compressed together into an ear or cone.

The account places Equisetums beyond Ferns in development and describes a transition between sheath leaves and fertile leaves in a collar at the cone's base. The cone may be considered a very rudimentary flower, while the annulus may represent a very early stage in the formation of a flower. The sporangia lie on the underside of the sporophylls, one at each angle, and are described as saclike structures opening inwardly through a longitudinal cleft. The spores are green, with walls composed of four distinct layers, of which the outer layer gradually separates except at one point.