Pea

The term pea originates from the Latin word pisum,[16] which is the latinisation of the Greek πίσον (pison), neuter variant form of πίσος (pisos) "pea".[17][18] It was adopted into English as the noun pease (plural peasen), as in pease pudding. However, by analogy with other plurals ending in -s, speakers began construing pease as a plural and constructing the singular form by dropping the -s, giving the term pea. This process is known as back-formation.[19]

Raw green peas are 79% water, 14% carbohydrates, 5% protein, and contain negligible fat (table). In a reference amount of 100 grams (3.5 oz), raw green peas supply 81 calories of food energy, and are a rich source (20% or more of the Daily Value, DV) of vitamin C (48% DV), vitamin K, thiamine, and manganese, with several B vitamins and dietary minerals in moderate amounts (11-16% DV) (table).

Split peas, raw (dried)

Yellow split peas
Nutritional value per 100 g (3.5 oz)
Energy	1,425 kJ (341 kcal)
Carbohydrates	60 g
Sugars	8 g
Dietary fiber	26 g
Fat	1 g
Protein	25 g
Vitamins	Quantity %DV†
Thiamine (B1)	61% 0.7 mg
Pantothenic acid (B5)	34% 1.7 mg
Folate (B9)	69% 274 μg
Minerals	Quantity %DV†
Iron	31% 4 mg
Units μg = micrograms • mg = milligrams IU = International units
†Percentages are roughly approximated using US recommendations for adults. Source: USDA FoodData Central

The pea karyotype consists of seven chromosomes, five of which are acrocentric and two submetacentric.[20] Despite its scientific popularity, its relatively large genome size (4.45Gb) made it challenging to sequence compared to other legumes such as Medicago truncatula and soybeans. The International Pea Genome Sequencing Consortium was formed to develop the first pea reference genome, and the draft assembly was officially announced in September 2019. It covers 88% of the genome (3.92Gb) and predicted 44,791 gene-coding sequences. The pea used for the assembly was the inbred French cultivar "Caméor".[21]

There are many varieties (cultivars) of garden peas. Some of the most common varieties are listed here. PMR indicates some degree of powdery mildew resistance; afila types, also called semi-leafless, have clusters of tendrils instead of leaves.[22] Unless otherwise noted these are so called dwarf varieties which grow to an average height of about 1m. Giving the vines support is recommended, but not required. Extra dwarf are suitable for container growing, reaching only about 25 cm. Tall varieties grow to about 2m with support required.[23]

• Alaska, 55 days (smooth seeded)
• Tom Thumb / Half Pint, 55 days (heirloom, extra dwarf)
• Thomas Laxton (heirloom) / Laxton's Progress / Progress #9, 60–65 days
• Mr. Big, 60 days, 2000 AAS winner
• Little Marvel, 63 days, 1934 AAS winner
• Early Perfection, 65 days[24]
• Kelvedon Wonder, 65 days, 1997 RHS AGM winner[25]
• Sabre, 65 days, PMR
• Homesteader / Lincoln, 67 days (heirloom, known as Greenfeast in Australia and New Zealand)
• Miragreen, 68 days (tall climber)
• Serge, 68 days, PMR, afila
• Wando, 68 days
• Green Arrow, 70 days
• Recruit, 70 days, PMR, afila[26]
• Tall Telephone / Alderman, 75 days (heirloom, tall climber)

Handful of pea pods for a stir fry

Some peas lack the tough membrane inside the pod wall and have tender edible pods.[27] There are two main types:[28]

• Snow peas have flat pods with thin pod walls. Pods and seeds are eaten when they are very young.
• Snap peas or sugar snap peas have rounded pods with thick pod walls. Pods and seeds are eaten before maturity.

The name sugar pea can include both types[27] or be synonymous with either snow peas or snap peas in different dictionaries.[29] Likewise mangetout (/ˈmɒ̃ʒˌtuː/; from French: pois mange-tout, "eat-all pea").

Snow peas and snap peas both belong to Macrocarpon Group,[30][31][32] a cultivar group based on the variety Pisum sativum var. macrocarpum Ser. named in 1825.[33] It was described as having very compressed non-leathery edible pods in the original publication.

The scientific name Pisum sativum var. saccharatum Ser. is often misused for snow peas. The variety under this name was described as having sub-leathery and compressed-terete pods and a French name of petit pois.[33] The description is inconsistent with the appearance of snow peas, and therefore botanists have replaced this name with Pisum sativum var. macrocarpum.[34]

Pod 'Blue Schokker'

Field Pea Plant in Bloom

The field pea is a type of pea sometimes called P. sativum subsp. arvense (L.) Asch. It is also known as dun (grey-brown) pea, Kapucijner pea, or Austrian winter pea, and is one of the oldest domesticated crops, cultivated for at least 7,000 years. Field peas are now grown in many countries for both human consumption and stockfeed. There are several cultivars and colors including blue, dun (brown), maple and white. This pea should not be confused with the cowpea (Vigna unguiculata) which is sometimes called the "field pea" in warmer climates.[35][36]

It is a climbing annual legume with weak, viny, and relatively succulent stems. Vines often are 4 to 5 feet (120 to 150 cm) long, but when grown alone, field pea's weak stems prevent it from growing more than 1.5 to 2 feet (45 to 60 cm) tall. Leaves have two leaflets and a tendril. Flowers are white, pink, or purple. Pods carry seeds that are large (4,000 seeds/lb), nearly spherical, and white, gray, green, or brown. The root system is relatively shallow and small, but well nodulated.[37]

The field pea is a cool-season legume crop that is grown on over 25 million acres worldwide. It has been an important grain legume crop for millennia, seeds showing domesticated characteristics dating from at least 7000 years ago have been found in archaeological sites around what is now Turkey. Field peas or "dry peas" are marketed as a dry, shelled product for either human or livestock food, unlike the garden pea, which is marketed as a fresh or canned vegetable. The major producing countries of field peas are Russia and China, followed by Canada, Europe, Australia and the United States. Europe, Australia, Canada and the United States raise over 4.5 million acres and are major exporters of peas. In 2002, there were approximately 300,000 acres of field peas grown in the United States.[38]

A basket of peas in pods

In modern times peas are usually boiled or steamed, which breaks down the cell walls and makes the taste sweeter and the nutrients more bioavailable. Along with broad beans and lentils, these formed an important part of the diet of most people in the Middle East, North Africa and Europe during the Middle Ages.[39] By the 17th and 18th centuries, it had become popular to eat peas "green", that is, while they are immature and right after they are picked.[40] New cultivars of peas were developed by the English during this time, which became known as "garden" or "English" peas. The popularity of green peas spread to North America. Thomas Jefferson grew more than 30 cultivars of peas on his estate.[41] With the invention of canning and freezing of foods, green peas became available year-round, and not just in the spring as before.

Peas in fried rice

Fresh peas are often eaten boiled and flavored with butter and/or spearmint as a side dish vegetable. Salt and pepper are also commonly added to peas when served. Fresh peas are also used in pot pies, salads and casseroles. Pod peas (snow peas and snap peas) are used in stir-fried dishes, particularly those in American Chinese cuisine.[42] Pea pods do not keep well once picked, and if not used quickly, are best preserved by drying, canning or freezing within a few hours of harvest.[43]

In India, fresh peas are used in various dishes such as aloo matar (curried potatoes with peas) or mattar paneer (paneer cheese with peas), though they can be substituted with frozen peas as well. Peas are also eaten raw, as they are sweet when fresh off the bush. Green Peas known as Hasiru Batani in Kannada are used to make curry and Gasi.[44] Split peas are also used to make dal, particularly in Guyana, and Trinidad, where there is a significant population of Indians.

Dried green peas

Dried peas are often made into a soup or simply eaten on their own. In Japan, China, Taiwan and some Southeast Asian countries, including Thailand, the Philippines and Malaysia, peas are roasted and salted, and eaten as snacks. In the Philippines, peas, while still in their pods, are a common ingredient in viands and pansit. In the UK, dried yellow or green split peas are used to make pease pudding (or "pease porridge"), a traditional dish. In North America, a similarly traditional dish is split pea soup.

Pea soup is eaten in many other parts of the world, including northern Europe, parts of middle Europe, Russia, Iran, Iraq and India.[45]

In Chinese cuisine, the tender new growth [leaves and stem] dou miao (豆苗; dòu miáo) are commonly used in stir-fries. Much like picking the leaves for tea, the farmers pick the tips off of the pea plant.

In Greece, Tunisia, Turkey, Cyprus, and other parts of the Mediterranean, peas are made into a stew with lamb and potatoes.

In Hungary and Serbia, pea soup is often served with dumplings and spiced with hot paprika.[46][47][48]

In the United Kingdom, dried, rehydrated and mashed marrowfat peas, or cooked green split peas, known as mushy peas, are popular, originally in the north of England, but now ubiquitously, and especially as an accompaniment to fish and chips or meat pies, particularly in fish and chip shops. Sodium bicarbonate is sometimes added to soften the peas. In 2005, a poll of 2,000 people revealed the pea to be Britain's seventh favourite culinary vegetable.[49]

Processed peas are mature peas which have been dried, soaked and then heat treated (processed) to prevent spoilage—in the same manner as pasteurizing. Cooked peas are sometimes sold dried and coated with wasabi, salt, or other spices.[50]

In North America pea milk is produced and sold as an alternative to cow milk for a variety of reasons.[51]

In East Asia, the sprouts or shoots of pea (豆苗;완두순) [52] were once dedicated cuisine when the plant was not highly available as nowadays. But now, when the plant can be easily grown, fresh pea shoots are available in supermarkets, and some people decided to grow them in their backyard.[53]

Frozen green peas

In order to freeze and preserve peas, they must first be grown, picked, and shelled. Usually, the more tender the peas are, the more likely that they will be used in the final product. The peas must be put through the process of freezing shortly after being picked so that they do not spoil too soon. Once the peas have been selected, they are placed in ice water and allowed to cool. After, they are sprayed with water to remove any residual dirt or dust that may remain on them. The next step is blanching. The peas are boiled for a few minutes to remove any enzymes that may shorten their shelf life. They are then cooled and removed from the water. The final step is the actual freezing to produce the final product.[54] This step may vary considerably; some companies freeze their peas by air blast freezing, where the vegetables are put through a tunnel at high speeds and frozen by cold air. Finally, the peas are packaged and shipped out for retail sale.

Pea flowers

In the mid-19th century, Austrian monk Gregor Mendel's observations of pea pods led to the principles of Mendelian genetics, the foundation of modern genetics.[55] He ended up growing and examining about 28,000 pea plants in the course of his experiments.[56]

Mendel chose peas for his experiments because he could grow them easily, develop pure-bred strains, protect them from cross-pollination, and control their pollination. Mendel cross-bred tall and dwarf pea plants, green and yellow peas, purple and white flowers, wrinkled and smooth peas, and a few other traits. He then observed the resulting offspring. In each of these cases, one trait is dominant and all the offspring, or Filial-1 (abbreviated F₁) generation, showed the dominant trait. Then he crossed members of the F₁ generation together and observed their offspring, the Filial-2 (abbreviated F₂) generation. The F₂ plants had the dominant trait in approximately a 3:1 ratio.

Mendel reasoned that each parent had a 'vote' in the appearance of the offspring, and the non-dominant, or recessive, trait appeared only when it was inherited from both parents. He did further experiments that showed each trait is separately inherited. Unwittingly, Mendel had solved a major problem with Charles Darwin's theory of evolution: how new traits were preserved and not blended back into the population, a question Darwin himself did not answer. Mendel's work was published in an obscure Austrian journal and was not rediscovered until about 1900.[57]

Some people experience allergic reactions to peas, as well as lentils, with vicilin or convicilin as the most common allergens.[58]

Favism, or Fava-bean-ism, is a genetic deficiency of the enzyme glucose-6-phosphate dehydrogenase that affects Jews, other Middle Eastern Semitic peoples, and other descendants of the Mediterranean coastal regions. In this condition, the toxic reaction to eating most, if not all, beans is hemolytic anemia, and in severe cases, the released circulating free hemoglobin causes acute kidney injury.[59][60]

Peas, like many legumes, contain symbiotic bacteria called Rhizobia within root nodules of their root systems. These bacteria have the special ability to fix nitrogen from atmospheric, molecular nitrogen (N₂) into ammonia (NH₃).[61] The chemical reaction is:

N₂ + 8H⁺ + 8e⁻ → 2NH₃ + H₂

Ammonia is then converted to another form, ammonium (NH+4), usable by (some) plants by the following reaction:

NH₃ + H⁺ → NH+4

The root nodules of peas and other legumes are sources of nitrogen that they can use to make amino acids, constituents of proteins. Hence, legumes are good sources of plant protein.[62]

When a pea plant dies in the field, for example following the harvest, all of its remaining nitrogen, incorporated into amino acids inside the remaining plant parts, is released back into the soil. In the soil, the amino acids are converted to nitrate (NO−3), that is available to other plants, thereby serving as fertilizer for future crops.[63][64]

Pea grading involves sorting peas by size, in which the smallest peas are graded as the highest quality for their tenderness.[65] Brines may be used, in which peas are floated, from which their density can be determined.[65]

A variety of diseases affect peas through a number of pathogens, including insects, viruses, bacteria and fungi.[66] In particular, virus disease of peas has worldwide economic importance.[67]

Additionally, insects such as the pea leaf weevil (Sitona lineatus) can damage peas and other pod fruits. The pea leaf weevil is native to Europe, but has spread to other places such as Alberta, Canada. They are about 3.5 millimetres (0.14 in)—5.5 millimetres (0.22 in) long and are distinguishable by three light-coloured stripes running length-wise down the thorax. The weevil larvae feed on the root nodules of pea plants, which are essential to the plants' supply of nitrogen, and thus diminish leaf and stem growth. Adult weevils feed on the leaves and create a notched, "c-shaped" appearance on the outside of the leaves.[68]

The pea moth can be a serious pest producing caterpillars the resemble small white maggots in the pea-pods. The caterpillars eat the developing peas making them unsightly and unsuitable for culinary use.[69] Prior to the use of modern insecticides, pea moth caterpillars were a very common sight in pea pods.