French bean (Phaseolus vulgaris)
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The common bean, Phaseolus vulgaris, is an herbaceous annual plant domesticated independently in ancient Mesoamerica and the Andes, and now grown worldwide for its edible bean, popular both dry and as a green bean. The leaf is occasionally used as a leaf vegetable, and the straw is used for fodder. Botanically, the common bean is classified as a dicotyledon. Beans, squash and maize comprised the “Three sisters” that provided the foundation of Native American agriculture. As a legume, beans provided the nitrogen-fixing bacteria which supplied that essential nutrient to the other two crops.
The common bean is a highly variable species. Bush varieties form erect bushes 20 – 60 cm tall, while pole or running varieties form vines 2 – 3 m long. All varieties bear alternate, green or purple leaves, divided into three oval, smooth-edged leaflets, each 6 – 15 cm long and 3 – 11 cm wide. The white, pink, or purple flowers are about 1 cm long, and give way to pods 8 – 20 cm long, 1 – 1.5 cm wide, green, yellow, black or purple in color, each containing 4 – 6 beans. The beans are smooth, plump, kidney-shaped, up to 1.5 cm long, range widely in color, and are often mottled in two or more colors.
As the common bean is a dicot, it germinates as such:
Before they are eaten, the raw bean seeds should be boiled for at least ten minutes to degrade a toxic compound - the lectin phytohaemagglutinin - found in the bean which would otherwise cause severe gastric upset. This compound is present in many varieties (and in some other species of bean), but is especially concentrated in red kidney beans and white kidney beans (Cannellini beans). Although in the case of dry beans the ten minutes required to degrade the toxin is much shorter than the hours required to fully cook the beans themselves, outbreaks of poisoning have been associated with the use of slow cookers whose low cooking temperatures may be unable to degrade the toxin. Sprouts of pulses high in haemaglutins should not be eaten. Kidney beans, especially, should not be sprouted.