Curly pondweed

Family Potamogetonaceae. These plants are entirely submerged in water; only during flowering do the small yellowish flowers, gathered in spikes, rise above the water and are pollinated by wind.

The leaves fully live up to the name. They are strongly wavy, with small marginal teeth, somewhat resembling certain brown seaweeds, and have three veins. The stems of curly pondweed are reddish and four-angled.