Legumes (Fabaceae) constitute the third largest plant family with around 700 genera and 20,000 species. Legume plants form root nodules through symbiosis with a soil microbe called rhizobia. This plant-microbe symbiosis in nodules mediates a harmonized exchange of chemical signals between host plants and rhizobia. Nodules are biologically divided into two different groups, i.e., indeterminate nodules and determinate nodules. Indeterminate nodules, represented by Trifolium repens (white clover) and Medicago truncatula, are initiated from the inner cortex to form a persistent nodule meristem, which allows continuous growth, and leads to the formation of elongated nodules, whereas in determinate legumes, nodules are mostly developed from outer cortical cells and form spherical nodules.
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