Legumes

Edible legumes

Legumes are plants that fall in the family Fabaceae, which formally was more commonly referred to as the Leguminosae. They are easily identified by their distinctive pods. Pulses are annual legumes that are cultivated for their seed. All the commercially grown species listed below are pulses, while the list of indigenous legumes eaten in southern Africa is of wild species that are little or not cultivated and some of these are perennials.

Domestication of pulses involved selection for the following traits (Zohary & Hopf 1994).

Retainment of seed in the pod. Many wild legumes have pods that burst open when mature, releasing their seeds. Domestication has involved selecting for pods that do not burst open or split open slowly. This enables them to be harvested without loss of seeds.
Larger seeds. Domesticated pulses generally have larger seeds, with the obvious advantage of having a higher food content.
Thinner seed coats. A thick seed coat protects the seed and also delays germination. By selecting for thinner seed coats, one is reducing germination delays and also the seed is more permeable to water.
Stiffer stems. Wild forms were often climbers or small, delicate plants. There was selection for plants that were free-standing, with stiffer stems that could be cultivated in open fields.
Reduced toxins. Wild plants often had chemical defences (toxins and antimetabolites) that made the seeds unpalatable to herbivores. Under the process of domestication there was selection for plants that lacked toxins or had them in reduced quantities.

The domestication of pulses went hand-in-hand with the domestication of grains. Whereas grains are rich in carbohydrates, pulses are rich in protein. Eaten in combination, one has a more balanced diet. Pulses serve as an important meat substitute.

The main reason that seeds of legumes contain high levels of protein is that legumes have a symbiotic association with root bacteria of the genus Rhizobium. These bacteria are able to convert atmospheric nitrogen into nitrogenous chemical compounds that can be used by the plant to synthesize amino acids and from these proteins. From a purely agricultural point of view there was a hand-in-hand relationship between pulses and grains: whereas grain crops used up nitrogen in the soil, legume crops added nitrogen to the soil. Rotation between these two crops therefore was important in maintaining soil fertility.

Each agricultural civilization therefore developed not only its own staple cereals but also its own legume crops:

Region	Grains domesticated	Pulses domesticated
West Asia through to Europe	wheat, barley	pea, lentil, broad bean, chickpea
Central America	maize	Phaseolus beans
South America	maize	groundnuts
Africa	African finger millet, pearl millet, sorghum	cowpea, jugo bean
Asia	rice, common millet and foxtail millet	soybean in China; mung bean, pigeon pea and others in India

Commercial species (pulses)

Arachis hypogaea (Peanut, Groundnut) Family: Fabaceae Groundnuts were domesticated by indigenous people in the region of Argentina and Bolivia over 4000 years ago. The seedpods mature underground, hence the name groundnuts. Peanuts are nutritious in that they contain 45-50% oil and 25-30% protein as well as having certain vitamins. However, peanuts infested with fungal aflatoxin and eaten in large quantities can cause liver cancer in people.
Cajanus cajan (Pigeon pea) Family: Fabaceae Evidence suggests that Pigeon pea originated in India and from there was introduced to East Africa around 4000 years ago. It is grown in semi-arid and subtropical areas of the world, including Asia, Africa and South America. In Africa the main countries growing Pigeon pea are Kenya, Malawi, Uganda, Tanzania and Nigeria, but it is also grown in southern Africa in warm regions. It is grown mainly as a subsistence crop: seeds are eaten and young pods are eaten as a vegetable.
Cicer arietinum (Chickpea) Family: Fabaceae Originates from south-eastern Turkey. Wild chickpeas were being harvested by people 9500 years ago, and by 8500 years ago there is evidence that chickpeas were being cultivated. The seeds have high levels of protein and are eaten whole or ground into flour that has a wide variety of uses. Hummus dip is made from ground up chickpeas and sesame oil.
Glycine max (Soybean) Family: Fabaceae Domesticated in northeastern China from the wild Glycine soja, the earliest evidence of cultivation dating to 3000 years ago.
Lens culinaris (Lentil) Family: Fabaceae Originates from the Near East and central Asia. People were harvesting wild lentils by 11200 years ago and by 8800 years ago lentils were being cultivated.
Phaseolus lunatus (Lima bean) Family: Fabaceae Lima Beans originate from Central and South America where they were domesticated at least 8500 years ago.
Phaseolus vulgaris (Green beans, Large white beans, Flageolet, Black bean, Borlotto bean, Red kidney bean, Cannellino bean, Sugar bean, Haricot bean) Family: Fabaceae Originate from Central and South America. The earliest archaeological evidence of domesticated bean seeds is from 7500 years ago at a site in mountainous northern Peru. Phaseolus vulgaris also includes Large white beans, Flageolet, Black bean, Borlotto bean, Red kidney bean and Cannellino bean.	Sugar beans Haricot beans Kidney beans
Pisum sativum (Pea) Family: Fabaceae Originates from the Near East, was being eaten by people at least 9500 years ago, and by 8500 years ago there is evidence of pea cultivation.
Vicia faba (Broad Bean) Family: Fabaceae Bean seeds and very young pods are eaten as a vegetable. Seeds have a high protein content of about 20-25%. Broad Bean was probably domesticated in the eastern Mediterranean region in the late Neolithic (about 6800- 4500 BC) but precise evidence is lacking and in addition we have no idea of the wild plant species from which it was derived.
Vigna subterranea (Jugo bean, Bambara groundnut, African groundnut) Family: Fabaceae Jugo bean is native to West Africa but is now grown widely as a crop in the tropical regions of Africa. It has the advantage of being able to be reasonably productive even under extreme conditions such as drought and poor soil. It is similar to Arachis hypogea (Groundnuts) in that the flowers curl down into the ground so that the pods end up developing and maturing underground. Otherwise, the two plants are quite different in appearance. Each pod has only one or two seeds. Seeds are eaten raw or cooked, or are ground into a flour.
Vigna radiata (Mung bean) Family: Fabaceae Mung beans originate from India and India remains a leading producer of this legume. Most mung beans are olive green in colour but they can also be yellow, brown, or mottled black. They are an excellent source of folic acid and a good source of magnesium, phosphorus and thiamin. Mung beans are an important food in rural areas of southern Africa, where the dry bean seeds are used or the beans themselves are eaten as a vegetable.
Vigna unguiculata (Cowpea) Family: Fabaceae Native to Africa, including southern Africa. It is an important commercial crop in Africa and is also grown as a subsistence crop. Seeds are stored dry and used in various dishes. The leaves and young pods are used fresh or dry as a green vegetable.

Indigenous species utilised in southern Africa

Information mainly from van Wyk and Gericke (2000)

Bauhinia petersiana (Wild coffee bean) Family: Fabaceae Seeds are roasted and eaten as nuts. Roasted seeds are also ground up and used as a coffee substitute.
Canavalia ensifolia (Jack bean) Family: Fabaceae Jack bean is a creeper that is cultivated in some rural regions of southern Africa. In order to make the seeds palatable, they need to be well-cooked and the seed coat removed. Seeds are also ground up and used as a coffee substitute.
Guibourtia coleosperma (Copalwood) Family: Fabaceae A tree that occurs in the Kalahari sands of northern Namibia and northern Botswana. Each seed is covered in a bright red aril. The !Khu Bushmen of NE Namibia remove the seed coat and eat the seed raw, roasted or pounded up. The oily aril is also eaten, especially under famine conditions. They use other parts of the plant for medicinal purposes.
Schotia spp. (boer-beans) Family: Fabaceae Seeds are edible. In Schotia afra they can evidently be eaten raw when green. Mature seeds need to be first cooked or roasted.
Tylosema esculentum (Marama bean) Family: Fabaceae This species grows in the Kalahari and the pod contains two to six large seeds, measuring about 2 cm in diameter and each weighing about 3 grams. Within the 2 mm thick seed coat is a tasty white nut. The potential of this species as a crop plants in arid regions is such that it is being grown in Texas, Australia and Israel, with a view to developing superior plants through selective breeding. Nuts are first roasted then eaten. Roasted nuts are also ground up and used as a coffee substitute or for porridge. The closely related Tylosema fassoglense also has edible nuts.
Vigna vexillata (Wild sweetpea) Family: Fabaceae This species is native to southern Africa and is evidently cultivated on a small scale in some areas for eating of the beans and seeds.

Publications

Anon. 2002. Encyclopedia of Foods. A Guide to Healthy Nutrition. Academic Press, San Diego, California.
Sauer, J.D. 1993. Historical geography of crop plants - a select roster. CRC Press, Boca Raton, Florida.
van Wyk, B.-E. & Gericke, N. 2000. People's Plants. A Guide to Useful Plants of Southern Africa. Briza Publications, Pretoria.