This ia a perennial that spreads via rhizomes. Its stems are hollow except at the nodes. They are ridged lengthwise. Sterile green stems are 1 to 3 feet tall and have many slender, whorled branches. The sterile stems form in late winter and persist through the growing season. Fertile, fleshy, brown, unbranched stems are 6 to 18 inches tall and are tipped by cone-like strobili that produce masses of green spores. The fertile stems are produced in winter and wither soon afterward. Giant horsetails are found along streambanks, in ditches, and in seepage areas.