Legumes are members of the family Fabaceae (formerly Leguminosae). The name is also used to refer to the fruit ("legume fruit") - these are usually pods of seeds (e.g. beans).
Legumes are noted for their capability to fix atmospheric nitrogen gas (N2) into soil nitrates (NO2) which can be used as "natural fertilizer" by other plants. This process is performed with a mutualistic symbiotic relationship with bacteria (rhizobia) in root nodules. These nodules also provide much greater levels of nitrogen to the host plant (compared to other plants), resulting in greater protein content in the plant and seeds.
Legumes are a very important agricultural crop. They are grown for their highly nutritious high-protein seeds (eg. beans), and they are also grown as a natural way of soil improvement. This latter advantage is often used in companion-planting; and was an important innovation in the Norfolk Four Course Rotation (crop rotation).
Example legumes include:
Use this tag for all general questions about legumes - eg. their use in companion planting, crop rotation, choosing a legume, etc. Most questions about growing specific legumes should use the relevant tag for the plant in question, instead.