Behind the Orchids and Sunflowers, the bean family is the third largest family. Now that several families have been combined there are about 18,000 species in 630 genera. To break it down further there are the Caesalpinioideae faboids with 150 genera and 2,700 species. The Faboideae have 429 genera and 12,615 species. The Mimosoideae have 40 genera and 2,500 species.
These plants often are associated with bacteria in nodes in their roots. This allows them to fix nitrogen and thus they are planted in soils that are low in nitrogen. Large mimosoid trees are seen frequently planted in the tropics with food crops underneath (putting nitrogen into the soil for the crops).
Systematics: Leaves are alternate, stipulate, and have a pulvinus. The ovary is superior and the fruit is usually a legume. Usually there are 10 stamen. Besides that there can be a lot of variation between the subfamilies.
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