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Lablab

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The lablab bean, known scientifically as *Lablab purpureus*, is a highly versatile legume. It belongs to the Fabaceae family. This plant is a multi-purpose crop used for food, animal fodder, and soil improvement. It is native to sub-Saharan Africa, though its exact origin remains uncertain. Some theories suggest it may have originated in India. Because it is so adaptable, it is now cultivated throughout the tropics and even in temperate regions like Italy.

Leiden University Library - Seikei Zusetsu vol. 18, page 038 - 白花稨豆 - Lablab purpureus (L.) Sweet, 1804
Leiden University Library - Seikei Zusetsu vol. 18, page 038 - 白花稨豆 - Lablab purpureus (L.) Sweet, 1804

Physically, the lablab is a variable plant. It can grow as an annual or a short-lived perennial vine. The wild version of the species is a perennial. The plant features thick stems that can grow quite long. Its leaves consist of three pointed leaflets that may be hairy on the underside. The flowers grow in clusters called racemes. These flowers can appear in white, blue, or purplish colors. The fruit is a legume pod, which is several centimeters long. These pods range in color from bright purple to pale green. Inside, each pod contains up to four seeds. These seeds can be white, brown, red, or black.

Taxonomy helps scientists classify the different types of lablab. The genus name *Lablab* was given by Robert Sweet. He based it on the previous name, *Dolichos lablab*, used by Carl Linnaeus. The biologist Bernard Verdcourt identified two cultivated subspecies. These are *Lablab purpureus* subsp. *bengalensis* and *Lablab purpureus* subsp. *purpureus*. There is also a wild subspecies called *Lablab purpureus* subsp. *uncinatus*. In Namibia, a special variant exists with lobed leaflets called *Lablab purpureus* var. *rhomboïdeus*. This variety shows how much the plant can change through breeding and evolution.

Growing lablab requires specific environmental conditions. It is most common in tropical and subtropical areas, especially in India and eastern or southern Africa. The plant is very hardy and can grow in soils ranging from sand to clay. It prefers a pH range between 4.5 and 7.5. This means it grows better in acidic soil than most other legumes. It thrives in temperatures between 18°C and 30°C. It also needs between 700 mm and 3000 mm of annual rainfall. While it prefers warmth, it can tolerate temperatures as low as 4°C for short periods. However, it cannot survive in waterlogged or flooded soils.

One of the most important features of the lablab is its ability to improve soil. This happens through a process called symbiosis. The plant works together with specialized bacteria called rhizobium. These bacteria live in the roots and perform nitrogen fixation. This means they take nitrogen from the air and turn it into a form plants can use. This process requires phosphorus to help the bacteria attach to the roots. Because of this, lablab is often used as a green manure. It can also be intercropped with other plants like maize. Growing lablab with maize can increase microbial diversity without losing maize yield.

Farmers use the lablab in many ways. They might plant seeds by broadcasting them or using the drillseed technique at a depth of 5 cm. For fodder, farmers often harvest the plants during the transition between vegetative and reproductive stages. This ensures the plants have high protein and low lignin. This makes the plants easier for livestock to digest. In some regions, cultivation has declined. In Africa, the common bean has replaced the lablab in many areas. This happened partly because of the many processing steps required for lablab. In other places, it is still grown in home gardens or mixed cropping systems.

Humans have consumed the lablab for thousands of years. In India, it has been cultivated since 2500 BC. In South Asia, the pods and beans are used in many dishes, such as curries and sautéed vegetables. In Kenya, the beans are known as *njahe* and are a traditional food for breastfeeding mothers. However, users must be careful during preparation. The beans contain cyanogenic glycosides. These are substances that turn into hydrogen cyanide if the beans are not cooked correctly. To make them safe, the beans must be boiled well with several changes of water. The leaves, flowers, and roots are also used in various food traditions around the world.

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