Name

Many different names in different parts of the world are used for the crop lentil.^[2] The first use of the word lens to designate a specific genus was in the 17th century by the botanist Tournefort.^[3] The word "lens" for the lentil is of classical Roman or Latin origin, possibly from a prominent Roman family named Lentulus, just as the family name "Cicero" was derived from the chickpea, Cicer arietinum, and "Fabia" (as in Quintus Fabius Maximus) from the fava bean (Vicia faba).^[4]

Systematics

The genus Vicia is part of the subfamily Faboideae which is contained in the flowering plant family Fabaceae or commonly known as legume or bean family, of the order Fabales in the kingdom Plantae.^[3]

Lentil plants in the field before flowering

The former genus Lens consisted of the cultivated L. culinaris and six related wild taxa. Among the different taxa of wild lentils, L. orientalis was considered to be the progenitor of the cultivated lentil and was generally classified as L. culinaris subsp. orientalis.^[2]

Lentil is hypogeal, which means the cotyledons of the germinating seed stay in the ground and inside the seed coat. Therefore, it is less vulnerable to frost, wind erosion, or insect attack.^[5]

The plant is a diploid, annual, bushy herb of erect, semierect, or spreading and compact growth and normally varies from 30 to 50 centimetres (12 to 20 in) in height. It has many hairy branches and its stem is slender and angular. The rachis bears 10 to 15 leaflets in five to eight pairs. The leaves are alternate, of oblong-linear and obtuse shape and from yellowish green to dark bluish green in colour. In general, the upper leaves are converted into tendrils, whereas the lower leaves are mucronate. If stipules are present, they are small. The flowers, one to four in number, are small, white, pink, purple, pale purple, or pale blue in colour. They arise from the axils of the leaves, on a slender footstalk almost as long as the leaves. The pods are oblong, slightly inflated, and about 1.5 centimetres (5⁄8 in) long. Normally, each of them contains two seeds, about 0.5 centimetres (1⁄4 in) in diameter, in the characteristic lens shape. The seeds can also be mottled and speckled. The several cultivated varieties of lentil differ in size, hairiness, and colour of the leaves, flowers, and seeds.

Lentils are self-pollinating. The flowering begins from the lowermost buds and gradually moves upward, so-called acropetal flowering. About two weeks are needed for all the flowers to open on the single branch. At the end of the second day and on the third day after the opening of the flowers, they close completely and the colour begins to fade. After three to four days, the setting of the pods takes place.^[2]

History

The cultivated lentil Lens culinaris subsp. culinaris was derived from its wild subspecies L. culinaris subsp. orientalis, although other species may also have contributed some genes, according to Jonathan Sauer (Historical Geography of Crop Plants, 2017).^[12] Unlike their wild ancestors, domesticated lentil crops have indehiscent pods and non-dormant seeds.^[12]

Lentil was domesticated in the Fertile Crescent of the Near East and then spread to Europe, the Middle East, North Africa and the Indo-Gangetic plain. The primary center of diversity for the domestic Lens culinaris as well as its wild progenitor L. culinaris ssp. orientalis is considered to be the Middle East. The oldest known carbonized remains of lentil from Greece's Franchthi Cave are dated to 11,000 BC. In archaeobotanical excavations carbonized remains of lentil seeds have been recovered from widely dispersed places such as Tell Ramad in Syria (6250–5950 BC), Aceramic Beidha in Jordan, Hacilar in Turkey (5800–5000 BC), Tepe Sabz (Ita. Tepe Sabz) in Iran (5500–5000 BC) and Argissa-Magula Tessaly in Greece (6000–5000 BC), along other places.^[13]

Soil requirements

Lentils can grow on various soil types, from sand to clay loam, growing best in deep sandy loam soils with moderate fertility. A soil pH around 7 would be the best. Lentils do not tolerate flooding or water-logged conditions.^[3]

Lentils improve the physical properties of soils and increase the yield of succeeding cereal crops. Biological nitrogen fixation or other rotational effects could be the reason for higher yields after lentils.^[14]

Climate requirements

The conditions under which lentils are grown differ across different growing regions. In the temperate climates lentils are planted in the winter and spring under low temperatures and vegetative growth occurs in later spring and the summer. Rainfall during this time is not limited. In the subtropics, lentils are planted under relatively high temperatures at the end of the rainy season, and vegetative growth occurs on the residual soil moisture in the summer season. Rainfall during this time is limited. In West Asia and North Africa, some lentils are planted as a winter crop before snowfall. Plant growth occurs during the time of snow melting. Under such cultivation, seed yields are often much higher.^[14]

Seedbed requirements and sowing

The lentil requires a firm, smooth seedbed with most of the previous crop residues incorporated. For the seed placement and for later harvesting it is important that the surface is not uneven with large clods, stones, or protruding crop residue. It is also important that the soil be made friable and weed-free, so that seeding can be done at a uniform depth.^[3]

The plant densities for lentils vary between genotypes, seed size, planting time and growing conditions, and also from region to region. In South Asia, a seed rate of 30 to 40 kilograms per hectare (27 to 36 pounds per acre) is recommended. In West Asian countries, a higher seed rate is recommended, and also leads to a higher yield. The seeds should be sown 3 to 4 centimetres (1+1⁄4 to 1+1⁄2 in) deep. In agriculturally mechanized countries, lentils are planted using grain drills, but many other areas still hand broadcast.^[3]

Cultivation management, fertilization

In intercropping systems – a practice commonly used in lentil cultivation – herbicides may be needed to assure crop health.^[14] Like many other legume crops, lentils can fix atmospheric nitrogen in the soil with specific rhizobia. Lentils grow well under low fertilizer input conditions, although phosphorus, nitrogen, potassium, and sulfur may be used for nutrient-poor soils.^[3]

Diseases

Below is a list of the most common lentil diseases.

Processing

A combination of gravity, screens and air flow is used to clean and sort lentils by shape and density. After destoning, they may be sorted by a color sorter and then packaged.

A major part of the world's red lentil production undergoes a secondary processing step. These lentils are dehulled, split and polished. In the Indian subcontinent, this process is called dal milling.^[3] The moisture content of the lentils prior dehulling is crucial to guarantee a good dehulling efficiency.^[3] The hull of lentils usually accounts for 6 to 7 percent of the total seed weight, which is lower than most legumes.^[15] Lentil flour can be produced by milling the seeds, like cereals.

Culinary use

Split red lentils (size 6 mm)

Lentils can be eaten soaked, germinated, fried, baked or boiled – the most common preparation method.^[3] The seeds require a cooking time of 10 to 40 minutes, depending on the variety; small varieties with the husk removed, such as the common red lentil, require shorter cooking times (and unlike most legumes don't require soaking). Most varieties have a distinctive, earthy flavor. Lentils with husks remain whole with moderate cooking, while those without husks tend to disintegrate into a thick purée, which may enable various dishes. The composition of lentils leads to a high emulsifying capacity which can be even increased by dough fermentation in bread making.^[16]

Lentil dishes

Lentils are used worldwide in many different dishes. Lentil dishes are most widespread throughout South Asia, the Mediterranean regions, West Asia, and Latin America.

Dal tadka (lentil soup)

In the Indian subcontinent, Fiji, Mauritius, Singapore and the Caribbean, lentil curry is part of the everyday diet, eaten with both rice and roti. Boiled lentils and lentil stock are used to thicken most vegetarian curries. They are also used as stuffing in dal parathas and puri for breakfast or snacks. Lentils are also used in many regional varieties of sweets. Lentil flour is used to prepare several different bread varieties, such as papadam.

They are frequently combined with rice, which has a similar cooking time. A lentil and rice dish is referred to in Levantine countries as mujaddara or mejadra. In Iran, rice and lentil is served with fried raisin; this dish is called adas polo. Rice and lentils are also cooked together in khichdi, a popular dish in the Indian subcontinent (India and Pakistan); a similar dish, kushari, made in Egypt, is considered one of two national dishes.

Lentils are used to prepare an inexpensive and nutritious soup throughout Europe and North and South America, sometimes combined with chicken or pork. In Western countries, cooked lentils are often used in salads.^[3] In Italy, the traditional dish for New Year's Eve is Cotechino served with lentils.

Lentils are commonly eaten in Ethiopia in a stew-like dish called kik, or kik wot, one of the dishes people eat with Ethiopia's national food, injera flatbread. Yellow lentils are used to make a non-spicy stew, which is one of the first solid foods Ethiopians feed their babies.

Lentils were a chief part of the diet of ancient Iranians, who consumed lentils daily in the form of a stew poured over rice.

Nutritional value

Boiled lentils are 70% water, 20% carbohydrates, 9% protein, and 0.4% fat (table). In a reference amount of 100 grams (3+1⁄2 ounces), cooked lentils (boiled; variety unspecified) provide 114 calories, and are a rich source (20% or more of the Daily Value, DV) of folate (45% DV), iron (25% DV), manganese (24% DV), and phosphorus (26% DV). They are a good source (10% DV) of thiamine (15% DV), pantothenic acid (13% DV), vitamin B₆ (14% DV), magnesium (10% DV), copper (13% DV), and zinc (13%) (table). Lentils contain carotenoids, lutein and zeaxanthin, and polyunsaturated fatty acids.^[17]