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Water Fern
Azolla japonica
アカウキクサ
A small aquatic fern floating in rice paddies, ponds, and marshes. Tiny overlapping leaves turn red in autumn to winter. It forms a symbiosis with cyanobacteria (Anabaena) for nitrogen fixation and is used as green manure in rice paddies.
Identification Points
- ✓Small fern (1–2 cm) floating on the water surface
- ✓Turns red in autumn to winter
- ✓Leaves arranged in 2 overlapping rows
Habitat
Rice paddies, ponds, marshes, and ditches
Season
Year-round (leaves turn red autumn–winter)
Phylogenetic Positionアカウキクサ科 →
Phylogenetic Position
Vascular plants > Polypodiophyta > Polypodiopsida > Salviniales > Azollaceae
Divergence Era
Cretaceous (ca. 80 million years ago–)
Evolution Notes
Azollaceae is a family of aquatic ferns that evolved the unique ability to fix nitrogen through symbiosis with cyanobacteria.
View on evolution timeline →Sources & References
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