Abstract

Azolla filiculoides a planktonic fern found floating on the surface of wetlands, ponds and rivers. Because of its ability to fix nitrogen through symbiotic cyanobacteria, it causes more rice production in paddy fields and is used as a green fertilizer. A. filiculoides was introduced from Philippine as a green fertilizer for rice crop to Iran, at 1986. The climatic condition of paddy fields, ponds and rivers of north of Iran was the best habitats for its regeneration and growth. Azolla has been distributed and has grown very fast in three Northern provinces of Iran, over 20 years. Now, this useful exotic plant, is a harmful weed in waters of the northern region of Iran because its fast regeneration, fast growth and high distribution.

Key word: Azolla filiculoides, cyanobacteria, exotic plant, mosquito fern.