Common duckweed

Covering the water surface in green

Common duckweed © Eero Haapanen

Common duckweed (Lemna minor) floats freely in the water, forming a seemingly uniform green disc on the surface of the water. It needs standing, nutrient-rich water in order to thrive. In the sea, it grows only in the most sheltered bays. The species spreads by clinging to birds, and in Helsinki it can be found in the ponds of even the outermost islets.