Description from Flora of China
Azolla japonica Franchet & Savatier; A. pinnata R. Brown var. japonica (Franchet & Savatier) Franchet & Savatier.
Plants more robust than Azolla imbricata. Lateral branches axillary, numbers of lateral branches less than fronds of stem; when in shallow water or wet places or plants in crowded situations, stems becoming erect and dorsal lobes changing to ventral ones. Sporangium with 3 floats on exospore; massulae of microsporangium covered with anchorlike hairs.
The whole plant of Azolla filiculoides is used as green manure and forage.
Cultivated and escaped, rice fields, ponds, ditches. Widely distributed in the Chang Jiang valley, also in S China, including Taiwan [Japan; NE Asia, Europe, North and South America, Pacific islands].