Marsilea ephippiocarpa Alston

Plants seasonally aquatic. Rhizome wide-creeping, initially green, brownish later, firmly herbaceous, terete or obtusely angular, to 1.5 mm in diameter, branched, rooting at the nodes, internodes to 38 mm long, initially sparsely appressed pilose, glabrous later, hairs ventrally attached, fusiform, subulate, or acicular, to 2 mm long. Stipe slender to stout, green initially, brown and glossy later, terete, to 90 mm long, to 1 mm in diameter, glabrous or sparsely set with hairs similar to those on the rhizome; pinnae herbaceous, pulvinate, variable in size and shape, narrowly cuneate-obtriangular, to broadly obdeltate, flanks straight or concave, outer margins rounded, entire to deeply crenate, to 16 mm long, to 12 mm wide, adaxially sparsely appressed pilose, hairs hyaline, ventrally attached, acicular, to 0.5 mm long, abaxially moderately appressed pilose, hairs hyaline to stramineous, ventrally attached, acicular, to 1 mm long. Sporocarps in dense clusters at the nodes, peduncle branched, pedicels to 2.5 mm long, appressed pilose when young, glabrous later, dark brown to blackish when fully mature, to 3 mm long, to 2.8 mm high, to 1.4 mm thick, typically saddle-shaped, dorsally almost always deeply concave, ventrally rounded, oblong to elliptic in dorsiventral cross-section, lateral ribs visible in mature specimens, 7-10, not anastomosing, raphe distinct, attached a half to a third the length of the sporocarp base, inferior tooth absent, superior tooth conspicuous, slender from a broadly conical base, acute or rarely subobtuse, initially densely appressed pilose, hairs hyaline to pale stramineous, ventrally attached, 5-7-celled, subulate, to 1.2 mm long.