String beans are the edible fruits of the bean plant, or the plants themselves. They are called string beans because of a fibrous string that runs along the length of the pod, which is usually removed before eating. The namesake string has mostly been bred out of modern varieties that are now found in supermarkets or garden supply stores. Commonly known as green beans, though they can be yellow or purple, pods are usually five to eight inches (12-20 cm) long. They are also known as snap beans because they can be snapped in half when they are at their freshest.
The names of string beans varieties usually refer to the type of plant they are grown on. Some string beans grow on low, bushy plants, typically from 12 to 24 inches tall (30-60 cm). The plants and beans are referred to as bush beans for this reason. The variety known as runner beans or pole beans are taller, bear beans on vines, and are trained to grow, or "run" up poles or other supporting frameworks. The two plants produce similar beans, but there is some variation among different breeds.
String beans are a member of the species Phaseolus vulgaris. Unlike other members of this species, such as black, red, or kidney beans, string beans are eaten in the pod before they are fully mature, when the seeds have not fully formed. These common beans, as they are sometimes known, are members of the Leguminosae family, and known as legumes. Like all beans of this species, they were first cultivated in South America and spread throughout the world after becoming known to Europeans.
Green beans are a popular garden plant that requires very little maintenance and will yield abundantly. They are a summer plant and have little tolerance for the cold temperatures of late spring and early autumn. Like other legumes, string beans are a nutritious source of fiber and protein, and prized for their taste when freshest. String beans also come in yellow and purple-colored varieties.
Some bean plants mature within a relatively fast fifty days, which is one of the reasons for their common presence in home gardens. Pole beans are known for having a longer production period, but bush beans can bear for weeks. Harvesting beans regularly can increase their production and cause them to bear beans longer.