Vallisneria

Vallisneria (named in honor of Antonio Vallisneri) is a genus of freshwater aquatic plant, commonly called eelgrass, tape grass or vallis. The genus is widely distributed in tropical and subtropical regions of Asia, Africa, Australia, Europe, and North America. Vallisneria is a submerged plant that spreads by runners and sometimes forms tall underwater meadows. Leaves arise in clusters from their roots. The leaves have rounded tips, and definite raised veins. Single white female flowers grow to the water surface on very long stalks. Male flowers grow on short stalks, become detached, and float to the surface. It is dioecious, with male and female flowers on separate plants. The fruit is a banana-like capsule having many tiny seeds. Sometimes it is confused with the superficially similar Sagittaria when grown submerged. This plant should not be confused with Zostera species, marine seagrasses that are usually also given the common name "eelgrass". Vallisneria has arched stems which cross over small obstacles and develop small planters at their nodes.

from Wikipedia