The soybean (U.S.) or soya bean (UK) (Glycine max) is a species of legume native to East Asia. The plant is classed as an oilseed rather than a pulse. It is an annual plant that has been used in China for 5,000 years as a food and a component of drugs. Soy contains significant amounts of all the essential amino acids for humans, and so is a good source of protein. Soybeans are the primary ingredient in many processed foods, including dairy product substitutes. The plant is sometimes referred to as greater bean or edamame, though the latter is more commonly used in English when referring to a specific dish.

The English word soy is derived from the Japanese pronunciation of 醤油 (しょうゆ, shōyu), the Japanese word for Soya sauce; soya comes from the Dutch adaptation of the same word.

Soybeans are an important source of vegetable oil and protein world wide. Soy products are the main ingredients in many meat and dairy substitutes. They are also used to make soy sauce, and the oil is used in many industrial applications. The main producers of soy are the United States, Brazil, Argentina, China and India. The beans contain significant amounts of alpha-linolenic acid, omega-6 fatty acid, and the isoflavones genistein and daidzein.

Classification

Like some other crops of long domestication, the relationship of the modern soy bean to wild-growing species can no longer be traced with any degree of certainty. It is a cultural variety with a very large number of cultivars.

The genus Glycine Wild. is divided into two subgenera (species), Glycine and Soja. The subgenus Soja (Moench) includes the cultivated soybean, G. max (L.) Merrill, and the wild soybean, G. soja Sieb.& Zucc. Both species are annual. The soybean grows only under cultivation while G. soja grows wild in China, Japan, Korea, Taiwan and Russia. Glycine soja is the wild ancestor of the soybean: the wild progenitor. At present, the subgenus Glycine consists of at least 16 wild perennial species: for example, Glycine canescens, and G. tomentella Hayata found in Australia, and Papua New Guinea.

Description and physical characteristics

Soy varies in growth, habit, and height. It may grow prostrate, not higher than 20 cm (7.8 inches), or grow up to 2 meters (6.5 feet) high.

The pods, stems, and leaves are covered with fine brown or gray hairs. The leaves are trifoliolate, having 3 to 4 leaflets per leaf, and the leaflets are 6–15 cm (2–6 inches) long and 2–7 cm (1–3 inches) broad. The leaves fall before the seeds are mature. The big, inconspicuous, self-fertile flowers are borne in the axil of the leaf and are white, pink or purple.

The fruit is a hairy pod that grows in clusters of 3–5, each pod is 3–8 cm long(1–3 inches) and usually contains 2–4 (rarely more) seeds 5–11 mm in diameter.