Marsilea costulifera D.L.Jones

Rhizome much-branched, glabrous except at the tips. Fronds 1–12 cm long, clustered. Stipes glabrous or scaly. Leaflets narrowly oblanceolate to cuneate, 1–12 mm long, 1–5 mm wide, arranged unequally with 2 leaflets spreading and 2 ± porrect, glabrous or scaly; outer margin entire, flat to rounded. Sporocarps in clusters; stalks 1–2 mm long, unbranched, glabrous; conceptacles 2.5–3 mm long, scaly, distinctly ribbed; upper surface concave; upper basal tooth prominent; lower basal tooth absent; apex of the stalk forming a less prominent, tooth-like protuberance.

Grows in shallow water and drying mud, rarely in moist grassland.