Question

Aquatic fern which supports the growth of blue-green algae, Anabaena and used to increase the yield of paddy crop is
A. Salvinia
B. Marsilea
C. Isoetes
D. Azolla

Answer 1

Ferns belong to Pteridophytes which are the first terrestrial plant groups to possess the vascular tissues, xylem, and phloem. Pteridophytes also include horsetails. Their main plant body is sporophyte and the spores develop into gametophytes. They are seen in cool, moist, damp, shady places as they require water for fertilization. They are grown for ornamental and medicinal purposes.

Complete answer:
Azolla is an aquatic fern that is also called a mosquito fern. They are seen in lakes, rivers, and other water bodies. It is very unique as it is a fast-growing plant that doesn’t require soil or land for its growth. It is a biofertilizer, biofuel, medicine, and food material. A symbiotic relationship is maintained between Azolla and the Blue-Green cyanobacteria, Anabaena. The Azolla provides the survival space for Anabaena and in return Anabaena converts the atmospheric nitrogen and gives it to Azolla. For the same reason, Azolla does not require soil for getting nitrogen as many land plants do. As a biofertilizer, Azolla is also used for the cultivation of paddy and many other crops for increasing their yield.
Salvinia is a floating fern that is commonly called water moss. It belongs to the family Salviniaceae. It is regarded as an aquatic weed in warm places. It has hydrophobic properties making it useful for mopping oil spills.
Marsilea is a water clover belonging to the family Marsileaceae. It has 4 leaves arranged in a clover shape. Some species of Marsilea are used as food and also grown as ornamentals. Some parts of the plant have enzymes that cause thiamine deficiency.
Isoetes are called quillworts belonging to the family of Isoetaceae under the class of lycopods. They are primitive plants grown as ornamentals.
The correct answer is option (D), Azolla.

Note: Azolla is believed to have existed since the Cretaceous period. Due to this very long age, Azolla and Anabaena have undergone co-evolution. When one organism in the symbiotic relationship undergoes evolutionary changes, the pair organism also undergoes similar evolutionary changes. It is coevolution. Azolla is used to control mosquito larvae in paddy fields.