Pea

Pea (Pisum sativum) is an annual herbaceous plant with soft stems that climb by tendrils, 0.5–2 m tall depending on the cultivar. The leaves are pinnately compound with 1–3 pairs of leaflets, usually ending in a branched tendril; the stipules are large, oval and clasp the stem. The flowers are the classic pea type with five petals arranged as standard (banner), two wings and a keel, coloured white, pink or purple; they are bisexual and normally self-pollinate before opening, so natural cross-pollination is rare. The fruit is a pod (legume) 5–10 cm long with a thin wall, containing 4–10 round seeds that are green when immature and yellow when dry, each weighing 0.1–0.36 g. There are groups of cultivars grown for the whole young pod (snow peas, sugar snap peas), for fresh seed (thin-podded garden peas) and for dry seed. The roots form symbiosis with nodule bacteria (Rhizobium leguminosarum) that fix nitrogen.

According to Kew POWO, Pisum sativum is native to the Mediterranean and South-West Asia, ranging from southern Europe (Spain, France, Italy, Greece, the Balkans) and North Africa (Morocco, Algeria, Tunisia, Libya, Egypt) to the Middle East (Turkey, the Levant, Iran, Iraq) and the Caucasus; the species has been introduced and is grown worldwide, including Vietnam. Based on recent genome studies, Kew now treats Pisum sativum as a synonym of Lathyrus oleraceus. Pea is one of the first domesticated crops: seeds have been found in the Fertile Crescent dating back about 10,000 years, and the site of Çayönü (south-eastern Turkey, about 9000 BP) is regarded as one of the earliest domestication sites. Population-genetic analysis indicates at least two domestication events: cultivated P. sativum derives from the wild P. sativum subsp. elatius (Mediterranean–Middle East), while the Ethiopian pea (P. abyssinicum) was domesticated independently. From the Fertile Crescent, pea spread west through the Danube valley, Greece and Rome into Europe, and east to Persia, India and China. Today it is an important cool-season food crop in Europe, North America, China, India and elsewhere. In Vietnam, pea is grown mainly in the winter–spring crop in the north and around Da Lat.

Chemically, pea seeds are rich in protein (about 20–25% of dry weight) and starch (about 40–50%); the protein is mainly storage globulin (7S/11S, making up 55–65% of total protein) plus albumin, rich in lysine but low in methionine. Pea starch has an intermediate amylose content (about 30–40%), giving a low glycaemic index (GI < 60) and containing resistant starch; the seed is also rich in fibre (seed coat and cell walls), raffinose-family oligosaccharides (RFOs) with prebiotic effects, vitamins (C, K, B1, folate) and minerals (iron, zinc, magnesium, selenium). Bioactive compounds include polyphenols (flavonoids and phenolic acids, concentrated in the seed coat and higher in dark-seeded varieties), saponins (soyasaponins, DDMP saponin, mildly bitter) and antinutritional factors: phytic acid (8.55–12.40 mg/g DW), lectins and trypsin inhibitors. Hydrolysed pea protein yields peptides with angiotensin-converting enzyme (ACE)-inhibitory and antioxidant activity; antimicrobial peptides from pea (such as LSDRFS, SDRFSY) and the peptide NuriPrep 1653 have been studied. The pea genome (4.45 Gb, 2n = 14) was published in 2019 (Kreplak et al., Nature Genetics).

Pea is an important food and vegetable crop: the fresh or dry seeds are used in soups, stews, stir-fries and salads; the young pods (snow peas, sugar snap peas) are eaten whole; the seeds are frozen, canned, milled into flour, or processed into pea protein and meat- and dairy-replacement products; the stems and leaves are used as animal feed and green manure, and the nitrogen-fixing plant improves soil. In research, Gregor Mendel used the garden pea to discover the laws of inheritance (published 1866), laying the foundation of genetics. A review in the British Journal of Nutrition (Dahl, Foster & Tyler, 2012) summarised the benefits of peas: low-GI starch, fibre that improves gut function, ACE-inhibitory (antihypertensive) and antioxidant peptides, and phytochemicals (polyphenols, saponins, oligosaccharides) with antioxidant and prebiotic effects. Reviews of pea protein (2020, 2023) highlight its low allergenicity, antioxidant, antihypertensive and gut-microbiota-modulating effects and its use as an emulsifier and gelling agent in foods. The pea reference genome (Kreplak et al., Nature Genetics, 2019) underpins genetics and breeding; a genomic study (2018) demonstrated at least two domestication events, and an analysis of 652 accessions (2022) modelled the spread of the crop.

As food, pea is nutritious but should be cooked: raw seeds contain lectins (phytohaemagglutinin) and trypsin inhibitors that can cause indigestion and bloating; soaking, cooking and fermentation reduce phytic acid (8.55–12.40 mg/g DW), lectins and trypsin inhibitors and improve mineral absorption. Raffinose-family oligosaccharides can cause mild bloating in sensitive people. Pea is one of the main allergenic foods in the EU; the main allergens are Pis s 1 (7S globulin) and Pis s 2. On conservation, according to Kew POWO the species is not regarded as threatened (it is domesticated and grown worldwide) and is not listed in the CITES appendices; however, its wild relatives — P. sativum subsp. elatius and P. fulvum — are valuable gene sources for disease resistance, cold tolerance and seed quality, and are conserved in many genebanks (worldwide pea germplasm holds more than 98,000 accessions, but less than 1% are wild forms).