Japanese name: オオアカウキクサ（大赤浮草） Scientific name:Azolla japonica
[Overview]
A small aquatic fern found in rice paddies and lakes, floating on the water surface.
The plant body is 1.5–7 cm long, and the roots hang down in the water; the root hairs fall off early and are not seen.
The stem branches densely in a pinnate manner, and scale-like leaves are borne alternately in two dense rows, overlapping like roof tiles.
The scale leaves are 0.2 cm long and divided into upper and lower lobes; the surface has a few granular projections or is smooth.
The leaves are green in summer, turn crimson in autumn, and in winter die back except for the tips.
The upper lobe of the leaf floats on the water surface, and Anabaena, a kind of cyanobacterium capable of nitrogen fixation, lives symbiotically in the cavity at its base.
The lower lobe of the leaf is submerged, and the sporangium clusters are borne among the underwater leaves; there are two types, megasporangium clusters and microsporangium clusters.
