Ruppia

a genus of aquatic perennial herbs of the family Ruppiaceae (formerly included in the family Potamogetonaceae). Except for the inflorescence, the plant is completely submerged in the water. The threadlike leaves are alternate or opposite. The small, bisexual flowers are in a two-flowered terminal spike. A perianth is absent. The fruit generally consists of four to six drupaceous lobes borne by long, thin pedicels. There are three or four species, distributed in the temperate and subtropical zones. The plants grow in saltwater and brackish shallows along the shores of seas and inland waters. There are two species in the USSR—R. maritima and tassel pondweed (R. spiralis). The plants serve as food for swimming birds.