Potamogetonaceae

The Potamogetonaceae are currently placed in the early diverging monocot order Alismatales by the Angiosperm Phylogeny Group. Their concept of the family includes the plants sometimes treated in the separate family Zannichelliaceae, but excludes the genus Ruppia. So circumscribed, the family currently consists of five genera totalling about 120 species of perennial aquatic plants. • Althenia • Groenlandia • Potamogeton • Stuckenia • Zannichellia }} Marine grasses families: Zosteraceae, Cymodoceaceae, Ruppiaceae and Posidoniaceae. Related families: Potamogetonaceae, Zannichelliaceae (not consistently). ==Characteristics==

The plants are all aquatic perennial herbs, often with creeping rhizomes and leafy branches. Their leaf blades can be either floating or submerged, and their stems are often joined. No stomata are present on the leaves. The flowers are tetramerous: the floral formula (sepals; petals; stamens; carpels) is [4;0;4;4]. The flowers have no petals. The fruit consists of one to four drupelets or achenes. ==References==