Amazon Frogbit

Native to South America, Amazon frogbit drifts across the water surface with small, rounded leaves that sit on top like lily pads in miniature. The undersides are spongy and buoyant, and each plant sends down a trailing mass of dark, feathery roots that can reach several inches into the water column.

Those roots are genuinely useful, not just decorative. Fry and shrimp hide in them constantly, and they pull nutrients directly out of the water, which helps keep algae in check.

Growth is fast when conditions are right. A handful can carpet a tank surface in a few weeks, so you'll be skimming out handfuls regularly to keep light reaching your other plants. It does need some airflow above the surface though. Stagnant, humid air causes the leaves to melt and rot quickly, which surprises people who assume floating plants are foolproof.

If you keep bettas or raise fry, this is one of the most practical plants you can add. Search planted betta tanks and you'll see it everywhere for good reason.