According to the NCERT text, fungi form symbiotic associations with plants called mycorrhiza. Many members of the genus Glomus form mycorrhiza. In this association, the fungal symbiont absorbs phosphorus from the soil and passes it to the plant. Rhizobium is a symbiotic nitrogen-fixing bacterium, Nostoc is a cyanobacterium, and Agaricus is a mushroom (fungus) typically saprophytic in nature.