Root nodules are commonly found on the roots of leguminous plants e.g. peas, beans, soybean, alfalfa, clover, etc. They provide a home for symbiotic nitrogen-fixing bacteria, Rhizobium.
Rhizobia is the general term used for different genera of nitrogen-fixing bacteria, e.g. Rhizobium, Bradyrhizobium, Azorhizobium, etc.
Plants cannot take atmospheric nitrogen directly. These bacteria fix atmospheric nitrogen to ammonia, which can be taken up by plants and utilized in the synthesis of essential macromolecules such as amino acids, nucleotides, etc.
