L., Sp. Pl. 992.1753 Monoecious, submerged, aquatic herb, rootless, to about 1 m long, dark green, unbranched or branched, with a single lateral branch produced at a node. Leaves whorled, 6-12 per node, 1-1.5 cm long, dichotomously dissected once or twice, the divisions mostly filiform, minutely denticulate, the whitish teeth on a broad base of green tissue. Flowers rare, unisexual, sessile, solitary in axil of one leaf of a whorl, ca 1 mm long; staminate flowers with sepals 10-15, basally connate; corolla lacking; stamens 10-20, spirally arranged on a flat receptacle; filaments very short; anthers linear-oblong, with a thickened, produced connective. Pistillate flowers with perianth similar to staminate flowers; ovary gradually tapered to slender style; pistil longer than sepals; stigma l, undifferentiated from style. Nuts also rare, axillary, tuberculate, with 2 spines at base, ca 4 mm long, tipped by the long persistent style. Croat 5738. This distinctive aquatic is not confused with any other in Panama. Cosmopolitan distribution. In Panama, it occurs probably in all lakes or slow-moving, freshwater habitats.