Wolffia arrhiza

Wolffia arrhiza is a rootless, stemless, leafless plant reduced to a single ellipsoidal cell body just 0.5–1.5 mm long — the smallest plant known to produce flowers, though these are visible only under magnification. It floats in dense colonies resembling green powder or fine algae on the water surface and is found across Europe, Asia, and Africa. In the aquarium it provides a nutritious live food supplement high in protein and is of immense biological curiosity for its extreme anatomical reduction.

Light: Medium surface light; grows well under standard aquarium lighting. CO2: Not required; absorbs nutrients directly from the water column. Planting: Introduce a small quantity to the surface; it will spread naturally. Maintenance: Thin the surface film regularly; can be easily siphoned off or skimmed with a net. Note: Can be difficult to distinguish from green surface algae — look for the faint spherical structure under magnification.