The plant in the given diagram is Azolla. Azolla is an aquatic fern that has symbiotic association with nitrogen fixing cyanobacterium Anabaena.
It propagates vegetatively and spreads in rice fields very rapidly.
It has a floating rhizome with small overlapping bilobed leaves and roots. Azolla provides habitat to Anabaena. The leaf shows dorsal and ventral lobe.
Anabaena filaments are present in the aerenchyma of dorsal lobe.
