Plants with jointed stems, with distinct nodes. Leaves small, whorled, fused into sheaths; tips remaining free, toothlike. Sporangia borne on peltate sporophylls aggregated in cones 0.3--10 cm. Spores green (except white in hybrids), all 1 kind. Gametophytes green, terrestrial, unisexual; male gametophytes smaller than female.
Plants perennial, homosporous, small to large, terrestrial, aquatic, or in shallow water. Rhizome creeping, sometimes erect or ascending, blackish brown, branched, with nodes; nodes with roots densely covered with trichomes or glabrous. Aerial stems annual or perennial, erect, monomorphic or dimorphic, green but lower nodes often blackish brown, terete, with nodes, hollow and with longitudinal canals in center, often with silica tubercles on epidermis, unbranched or with whorled branches; internodes with longitudinal ridges and grooves. Leaves reduced, scalelike, whorled; lower portion fused to form a collarlike sheath around base of internode; upper portion lobed. Strobili conelike, terminal on stem or branches, terete or ellipsoid, sometimes stalked; sporophylls whorled, peltate, hexagonal in surface view, imbricate, with 5-10 sporangia per sporophyll. Sporangia saclike, in whorls on abaxial side of sporophylls. Spores green, subglobose or globose, 35-70 μm in diam., each with 4 spirally curled, white filaments (elaters) that uncurl upon drying, without colpi, with thin and transparent perispores; perispores with granular ornamentation. Gametophytes growing at or near soil surface, green, disk- to cushion-shaped, irregularly lobed. x = 108.
Aerial stems erect, uniform or of two kinds, fertile and sterile, hollow, ribbed; arising from creeping subterranean, often very deep, rhizomes; producing whorls of branches at the nodes; some species produce tubers borne singly or in rows like strings of beads, from the rhizomes near the roots
Leaves reduced, in whorls, those of each whorl being united to form a sheath around the stem at each node
Aerial stems erect, hollow, ribbed, arising from creeping subterranean rhizomatous stems and producing whorls of branches at the nodes