Aquarium plant grown from tissue culture in a closed cup.

Riccia fluitans is a small, cosmopolitan liverwort which, depending on the conditions, grows 1-5 cm tall. Riccia is actually a floating plant, but the Japanese Takashi Amano has inspired many aquarists to keep Riccia fluitans submerged under water. It is held down by tying it to a rock with a piece of fishing line. New shoots seek the surface, so it is necessary to occasionally prick it with scissors. Under water, Riccia fluitans thrives best when CO2 is added, and when the growth conditions are good, small oxygen bubbles form in the leaf tips. As a traditional floating plant, it provides good protection for fish fry.