Hydrocharis laevigata

Amazon Frogbit is a floating plant from the wetlands of Central and South America, forming compact rosettes of round, bright-green leaves on the water surface. Each leaf has a spongy, air-filled underside — aerenchyma — that keeps the plant buoyant and gives it the alternative name South American Spongeplant. It spreads rapidly via stolons, producing daughter rosettes at intervals, and can cover the open water section of a paludarium within weeks under good light. Leaves must be kept dry from above: condensation or splashing causes rapid rot, which is why it does best in open-top setups rather than sealed enclosures.