QUILLWORT

(Isoetes species), any of more than 60 species of small plants that constitute the genus Isoetes, of the order Isoetales (class Lycopsida). They are spore-bearing plants with grassy, spikelike leaves, native mostly to swampy, cooler parts of northern North America and Eurasia. The spirally arranged, quill-like leaves are divided into cavities that contain one central conducting strand. The leaves rise from a cormlike or tuber-like base, with roots below. A large, round-to-oblong spore capsule is sunk into each leaf base, where a small, thin structure known as a ligule also occurs. Quillworts grow submerged in water all or part of the year. A few species are strictly terrestrial. The common quillworts I. lacustris of Eurasia and the very similar North American species I. macrospora are aquatic. Their stiff, dark green, recurved, spiky leaves grow around a stumpy base. Italian quillwort (I. malinverniana) has longer, spiralling leaves that float on the water surface. Sand quillwort (I. histrix), an inconspicuous European terrestrial, has very narrow, five- to seven-centimetre- (two- to three-inch-) long leaves that curl back to the ground from a fat, white, tufted base.