The frogbit (Hydrocharis morsus-ranae) is like a miniature yellow or white water-lily. Unlike water-lilies, the frogbit is not anchored to the bottom of the water body, but floats free, taking in nutrients directly from the water.
It propagates by forming runners. In the autumn, the runners form into onion-like winter buds, which detach from the mother plant and sink to the bottom. In the following spring, the winter buds start to spread and form gas bubbles, which help them rise to the surface. The buds then start to grow and form floating leaves.
The frogbit flowers rarely in Finland, only in the hottest summers. The only places in Helsinki where you can see frogbits are the duckboards by the Pornaistenniem bird hide and the old discharge ditch of the Viikki water treatment plant. There the plants have found suitable standing water that won’t wash them away from their habitat.