Flora of Panama

Abstract

Plants herbaceous, annual or rarely perennial, aquatic, submersed in fresh or brackish waters, monoecious or dioecious. Stems slender, much branched, rooting at the lower nodes; lower internodes elongate, the upper internodes reduced. Leaves subopposite or appearing whorled because of reduced internode length, sessile, each divided into lamina and auricle; laminas linear and flattened, 1nerved, the margins usually serrulate; auricles variously shaped, each enclosing a pair of tiny hyaline scales, the auricle margins usually spiny-toothed. Flowers axillary, sessile, solitary or clustered, each usually enclosed in a membranous involucre, the perianth absent; staminate flowers each consisting of a single stamen, the anthers 1or 4-thecate, dehiscing vertically, the filaments at first short, elongating slightly at anthesis; carpellate flowers each consisting of a single l-ovuled carpel, the placentation basal, the styles solitary, each divided into 2-4 subulate stigmatic lobes. Fruit achene-like, the pericarp closely enveloping the seed, areolate; seeds without endosperm, areolate.