Plants floating or rooted. Sterile leaves deltate to cordate to ovate. Petiole of sterile leaf 1--19 cm, usually inflated, in some near base, but in most inflated nearer blades. Blade of sterile leaf 2--4-pinnate, 5--33 × 4--29 cm, simple and palmately 3-lobed (ternate), or pinnately 5-lobed or pinnate near base; proximal pinnae or veins of lobes usually opposite. Fertile leaves deltate to cordate to reniform, 9--50 × 8--36(--50) cm. Petiole of fertile leaf 4--25 cm. Blade of fertile leaf 1--4-pinnate; terminal segments narrow, linear. Sporangia usually crowded between segment midvein and revolute margin, with 0--10(--40) indurate annulus cells. Spores 32 per sporangium, 70--100 µm diam. 2 n = 78.

Aquatic to semiaquatic; in swamps, bogs, canals, ponds, lakes, ditches, marshes; 0--25 m; Fla., La.; West Indies; Central America; South America; se Asia in Vietnam.

Ceratopteris pteridoides is usually easily recognized by its sterile leaf morphology, which varies considerably with habitat. Leaves intermediate between sterile and fertile are fairly common, with various degrees of laminar development of the fertile segments. Some fertile leaves have quite broad segments with rows of sporangia along the margins only. Ceratopteris pteridoides is sexual and diploid and is incompletely reproductively isolated from the diploid C . richardii . Hybrids synthesized by L. G. Hickok (1977) result in 40% viable spores.