Groundnut
The groundnut (Arachis hypogaea), commonly known as the peanut, is a species of legume in the family Fabaceae, native to South America in the region spanning southern Bolivia to northern Argentina.[1] This annual herbaceous plant exhibits a distinctive geocarpic growth habit, where its yellow, self-pollinating flowers develop into pods that push underground after fertilization, maturing into elongated legumes containing one to three seeds each.[2] Reaching heights of 0.75 to 1.5 feet with spreading or erect stems and compound leaves, the groundnut thrives in sandy, well-drained soils with a pH of 6.0 to 8.0 under full sun conditions, typically requiring 120 to 150 days from planting to harvest.[2] Originating from pre-Columbian cultivation in the Andes, the groundnut was domesticated approximately 4,000 years ago through hybridization of wild progenitors and spread globally following European colonization, becoming a staple crop in tropical and subtropical regions.[1] As of 2024, it is one of the world's major oilseed crops, with leading producers including China, India, and the United States, where annual global production exceeds 50 million metric tons (51.3 million tons projected for 2025), valued for its high oil content (up to 50% in seeds) and protein (25-30%).[3][4] The plant's nitrogen-fixing root nodules enhance soil fertility, supporting sustainable agriculture, while its seeds are processed into food products like peanut butter, oil, and snacks, as well as animal feed and industrial uses such as biodiesel.[2] However, groundnut cultivation faces challenges from pests, diseases like leaf spot, and its status as a major allergen due to seed proteins such as Ara h 1-3, affecting approximately 1-2% of the population in the United States.[5] Groundnut varieties are classified into four main market types—Runner, Virginia, Spanish, and Valencia—each suited to specific uses and growing conditions, with ongoing breeding efforts focused on improving yield, disease resistance, and nutritional quality through genomic tools and wild relative hybridization, including recent advances in genome sequencing as of the 2020s.[6] Economically, it supports rural livelihoods in developing countries and contributes to global food security, though climate variability and aflatoxin contamination from fungal infections pose ongoing risks to production.[7]Taxonomy and description
Botanical classification
The groundnut, known scientifically as Arachis hypogaea L., is classified within the family Fabaceae (Leguminosae), subfamily Faboideae, tribe Dalbergieae, genus Arachis L., and specifically in section Arachis of that genus.[8] This allotetraploid species (2n = 4x = 40) is the sole cultivated member of the genus, distinguished by its underground fruit development and adaptation to diverse agroecological zones.[9] The taxonomic structure of A. hypogaea recognizes two primary subspecies: A. hypogaea subsp. hypogaea and A. hypogaea subsp. fastigiata Waldron. Subspecies hypogaea encompasses two botanical varieties—var. hypogaea (characterized by glabrous leaflets and typically two seeds per pod) and var. hirsuta J. Burkart (with hairy leaflets and up to four seeds per pod)—reflecting primitive runner-type growth habits. Subspecies fastigiata includes four varieties: var. fastigiata (erect habit with sequential branching), var. vulgaris Harz (clustered pods with two seeds), var. peruviana Krapov. & W.C. Greg. (strongly reticulate pods with prominent ribs), and var. aequatoriana Krapov. & W.C. Greg. (hairy leaflets and equatorial distribution). This classification, based on morphological traits like branching patterns, pod reticulation, and seed number, underscores the species' intraspecific diversity and informs breeding strategies.[8] Evolutionary origins trace A. hypogaea to southern South America, particularly the regions of southeastern Bolivia, northwestern Argentina, and Paraguay, where the genus Arachis likely emerged. The species arose through a single hybridization event between two wild diploid progenitors: Arachis duranensis Krapov. & W.C. Greg. (contributing the A subgenome) and A. ipaensis Krapov. & W.C. Greg. (contributing the B subgenome), followed by chromosome doubling to form the allotetraploid AABB genome. This neopolyploidy event, estimated at approximately 3.9 million years ago, conferred reproductive isolation and hybrid vigor, enabling domestication around 3,500–4,000 years ago without a direct wild progenitor equivalent to the cultivated form. The closest wild relative is the tetraploid A. monticola Krapov. & Rigoni, which shares the AABB genome and can form fertile hybrids with A. hypogaea.[9][10] Genetic diversity in A. hypogaea is limited due to its single origin and self-pollinating nature, with higher variation observed in subsp. fastigiata compared to subsp. hypogaea. Diploid ancestors like A. duranensis and A. ipaensis provide critical germplasm for introgression breeding to enhance traits such as disease resistance and yield. Modern genomic studies, including whole-genome sequencing of progenitors and cultivars, have mapped subgenomic structure, identified duplicated genes from allotetraploidy, and facilitated marker-assisted selection, revealing that the A subgenome is more conserved while the B subgenome shows greater divergence. These insights support efforts to broaden the narrow genetic base of cultivated groundnut through interspecific hybridization.[11][12]Plant morphology and growth
The groundnut (Arachis hypogaea) is an annual herbaceous legume characterized by upright or prostrate stems that grow to a height of up to 50-60 cm and can spread up to 100 cm, depending on the variety.[13] The stems are cylindrical and smooth at the base, becoming angular and hairy with age, while the leaves are pinnate with two to three pairs of elliptical leaflets, each 1-3 inches long and less than 1 inch wide, featuring a prominent mid-vein and entire margins.[2] These leaves partially fold at night, aiding in water conservation.[13] The plant produces small, yellow, pea-shaped flowers that are self-pollinating through cleistogamy, occurring primarily at night in the leaf axils, with blooming typically beginning 30-40 days after planting.[13] Following pollination, the process of geocarpy ensues, where the fertilized ovaries elongate into pegs that elongate to 2–15 cm and penetrate the soil to depths of 1–7 cm, allowing pod development underground.[13] The resulting pods are cylindrical legumes, 2-5 cm long and less than 1 inch wide, containing 1-4 seeds enclosed in a woody pericarp with constrictions between seeds.[13] The root system features a taproot extending up to 150 cm deep with lateral branches reaching 60-80 cm, supporting effective water and nutrient uptake, and includes nitrogen-fixing nodules formed in symbiosis with rhizobia bacteria, which enhance soil fertility.[13] Growth progresses through distinct stages: vegetative development from emergence (6-14 days after planting) to the formation of multiple nodes; reproductive phases starting with beginning bloom (R1, 20-40 days), followed by peg initiation (R2, 36-75 days), pod swelling (R3-R4, 45-75 days), and seed filling (R5-R6, 55-130 days).[14][13] Groundnut plants exhibit adaptations to drought and heat, with deep roots enabling access to subsoil moisture and the ability to recover from water stress by producing new flower flushes upon rewatering, though temperatures above 35°C can reduce flower production.[13] Pod maturation typically occurs 120-150 days after planting, varying by variety and environmental conditions, marking the transition to harvest maturity when 70-75% of pods show pericarp and testa coloration.[2][14]Cultivation and production
History of domestication and spread
The groundnut, or peanut (Arachis hypogaea), was domesticated approximately 3,500 to 4,000 years ago in the Andean region of South America, particularly in what is now southern Bolivia and northern Argentina, through hybridization of wild diploid species such as A. duranensis and A. ipaensis.[15][16] Archaeological evidence indicates that early cultivation involved selective breeding for larger seeds and improved yield, transforming the wild progenitor into a staple crop suited to diverse agroecological niches across the continent.[17] Prior to European contact, indigenous peoples in South America, including the Inca and other pre-Columbian cultures, utilized groundnuts extensively for food, medicine, and rituals, often incorporating them into offerings and burials as symbols of fertility and sustenance.[18] By the 1500s, Spanish explorers had spread the crop northward to Mexico, where it integrated into Mesoamerican agriculture, while Portuguese traders disseminated it to the Caribbean and Brazil, facilitating its adaptation to tropical lowlands.[19] These early transatlantic movements laid the foundation for the crop's role in colonial economies, though initial adoption in Europe remained limited due to climatic constraints. During the 16th to 19th centuries, groundnuts were introduced to Africa and Asia primarily through Portuguese and Dutch colonial networks, often via slave trade routes that connected South American ports to West African and Indian Ocean outposts.[20] In West Africa, the crop quickly supplanted native groundnut species in local diets and export agriculture, with forced labor on plantations driving large-scale production in regions like Senegal and Gambia by the mid-19th century.[21] In Asia, Portuguese merchants facilitated its entry into India and Southeast Asia around the 16th century, where it became a key oilseed and snack food under colonial promotion. In the American South, post-1800s cultivation surged after the Civil War, as agronomist George Washington Carver advocated peanuts for soil nitrogen fixation to restore depleted cotton lands, elevating it from a subsistence crop to a vital cash commodity by the early 20th century.[22][23] In the 20th century, targeted breeding programs developed influential cultivars like the Runner and Virginia types, enhancing disease resistance, yield, and market quality for global trade.[24] The Runner cultivar, originating in the southeastern United States in the 1970s, improved shelling efficiency and flavor for confectionery uses, while the Virginia type, refined earlier in the century, supported larger-kernel varieties ideal for roasting and export. Post-World War II, international aid and colonial schemes, such as Britain's Groundnut Scheme in Tanganyika (now Tanzania), spurred expansion in Africa and Asia, boosting production to meet rising global demand for oils and proteins amid food shortages.[25] This era marked groundnut's transition to a major tropical commodity, with breeding advancements enabling adaptation to new regions and intensification of cultivation worldwide.Major producing regions and statistics
Groundnut, also known as peanut, is primarily cultivated in tropical and subtropical regions, with Asia and Africa dominating global production. As of November 2025, the USDA estimates worldwide groundnut production for the 2024/25 marketing year at approximately 51.27 million metric tons, reflecting revisions from earlier projections due to variable weather conditions including droughts in African regions.[3] China remains the largest producer, accounting for over one-third of the global output with an estimated 19 million metric tons, supported by extensive cultivation across 4.86 million hectares and yields averaging 3.91 tons per hectare.[3] India follows as the second-largest producer at 7.2 million metric tons, though its yields are lower at 1.31 tons per hectare due to rainfed farming on 5.5 million hectares.[26] Other major producers include Nigeria (4.3 million metric tons, yield 1.25 tons per hectare on 3.45 million hectares), the United States (2.92 million metric tons, with high yields enabled by mechanization), and Sudan (1.39 million metric tons, yield approximately 0.70 tons per hectare on 2.0 million hectares).[27][28] Global average yields range from 1.5 to 2.5 tons per hectare, with significant variations: advanced mechanized systems in the United States and parts of China achieve 3-4 tons per hectare, while sub-Saharan African countries often see 0.5-1.25 tons per hectare due to limited irrigation and soil challenges.[3] These disparities highlight the crop's sensitivity to agronomic inputs and climate factors, such as droughts impacting yields in Sudan and Nigeria, contributing to downward revisions in 2024/25 estimates.[3] Economically, groundnut plays a vital role in rural livelihoods, particularly in developing countries where it supports smallholder farmers and contributes to food security and income diversification. International trade in groundnuts, primarily in-shell and shelled forms, was valued at about $4.41 billion in 2024, with major exporters including Argentina and the United States supplying global markets.[29] This trade underscores groundnut's importance in agricultural economies, though production trends are increasingly influenced by climate variability, which has led to yield fluctuations in African regions over recent years.[3]| Country | Production (million metric tons, 2024/25) | Area (million hectares) | Yield (tons/hectare) |
|---|---|---|---|
| China | 19.00 | 4.86 | 3.91 |
| India | 7.20 | 5.50 | 1.31 |
| Nigeria | 4.30 | 3.45 | 1.25 |
| United States | 2.92 | 0.77 | 3.79 |
| Sudan | 1.39 | 2.00 | 0.70 |
Agronomic practices
Groundnut thrives in well-drained sandy loam or sandy clay loam soils with a pH range of 5.5 to 7.0, as these conditions facilitate peg penetration and pod development while minimizing waterlogging risks.[30][31][32] Soils with high clay content (>20%) or salinity should be avoided, and crop rotation with cereals is recommended to prevent disease buildup and maintain soil fertility.[30][32] Planting occurs at a sowing density of 10-20 plants per square meter, achieved through row spacings of 45-60 cm and intra-row spacings of 10-20 cm, depending on variety type (bunch or runner).[30][31] Seed rates typically range from 50-100 kg per hectare, with planting depths of 4-5 cm to ensure uniform emergence, and optimal soil temperatures between 20-30°C for germination.[30][32] Sowing is timed to coincide with the onset of adequate rainfall or irrigation availability, often in the rainy season for rainfed systems. Groundnut is largely rainfed, requiring 500-1000 mm of evenly distributed seasonal rainfall, with critical water needs during flowering and pod formation stages; supplemental irrigation at 7-10 day intervals may be applied in drier conditions using furrow or sprinkler methods.[30][31][32] As a legume, it fixes atmospheric nitrogen, reducing the need for N fertilizers, but phosphorus and potassium applications of 20-40 kg per hectare are often recommended based on soil tests to support pod filling and overall growth.[30][32] Organic manures (3-5 t/ha) or gypsum (250-500 kg/ha) can further enhance soil calcium levels, particularly at pegging.[30][31] Harvesting takes place 120-150 days after planting, when 70-80% of pods reach maturity, indicated by darkened hulls and full seed development, to avoid yield losses from sprouting or aflatoxin contamination.[30][31] Pods are dug using hand tools, hoes, or mechanical diggers to minimize damage and loss, followed by field drying for 2-3 days.[30][32] Post-harvest, plants are inverted to dry further in the sun, aiming for 8-10% moisture content before storage in ventilated conditions to prevent mold.[30][31]Uses and processing
Culinary and food applications
Groundnuts, commonly known as peanuts, are widely consumed directly as snacks in raw, roasted, or boiled forms, providing a versatile and nutritious option for everyday eating. Roasting enhances their nutty flavor and crunch, making them a popular choice in markets and homes around the world, while boiling softens the kernels for a milder taste often enjoyed in regions like the southern United States and parts of Africa.[33][34] One of the most iconic processed forms is peanut butter, created by roasting and grinding shelled peanuts into a smooth or chunky paste, typically with the addition of 1-2% salt to balance flavors and act as a preservative. This simple yet transformative process originated in the early 20th century and has become a staple spread for sandwiches, baking, and cooking worldwide.[35][36] In global cuisines, groundnuts serve as key ingredients in savory and sweet dishes, showcasing their adaptability. In West African cooking, they form the base of rich stews like mafe or groundnut soup, where ground kernels thicken sauces with vegetables, meat, or fish for hearty meals. Indian cuisine features them in tangy chutneys blended with chilies, garlic, and spices as accompaniments to dosas and idlis, or in sweets like chikki, a brittle made by mixing roasted peanuts with melted jaggery. Southeast Asian dishes, such as Indonesian and Thai satays, rely on groundnut sauces—creamy mixtures of blended peanuts, coconut milk, and spices—drizzled over grilled meats for a signature sweet-spicy profile. In Mexican cuisine, groundnuts add depth to mole poblano, a complex sauce incorporating roasted and ground peanuts alongside chilies, chocolate, and seeds, traditionally served over poultry.[34][37][38][39] Peanut oil, extracted from kernels through pressing, is prized for frying and stir-frying due to its high smoke point and mild flavor, yielding approximately 40-50% oil by weight depending on the variety and method. This oil's stability makes it ideal for high-heat culinary applications across Asian and Western kitchens.[40] Beyond basic preparations, groundnuts are transformed into various processed foods that expand their dietary roles. Peanut flour, produced by defatting and grinding kernels, is incorporated into baking for gluten-free breads, cookies, and coatings, imparting a nutty taste and boosting nutritional value without overpowering other flavors. Peanut milk, a creamy plant-based alternative, is made by soaking, blending, and straining peanuts, then used in beverages, smoothies, or desserts as a dairy substitute. Regional innovations include Japanese jimami tofu from Okinawa, a jiggly, soy-free block formed by coagulating peanut milk with starch for use in salads or soups, and further variations of peanut-based moles in Latin American recipes that highlight their thickening properties.[41][42] Proper storage is essential to maintain groundnut quality and prevent rancidity from their high oil content. Intact pods can be stored in cool, dry conditions for 6-12 months, while shelled kernels, kept in airtight containers at temperatures below 10°C (50°F) and low humidity, retain freshness for up to 2 years, though monitoring for moisture and pests is recommended.[43][44]Industrial and non-food uses
Groundnut oil, extracted from the seeds of Arachis hypogaea, serves as a key raw material in various industrial applications due to its favorable fatty acid profile, including approximately 50% oleic acid content, which contributes to its stability and versatility.[45] This oil is processed into biodiesel through transesterification, providing a renewable fuel alternative with properties comparable to conventional diesel, as demonstrated in studies using refined groundnut oil feedstocks.[46] Additionally, its low to moderate iodine value of 85-105, indicating moderate unsaturation, makes it suitable for manufacturing soaps, detergents, and lubricants, where it acts as an emollient and stabilizer in formulations.[47] Byproducts from groundnut processing offer significant non-food value. The press cake remaining after oil extraction contains 40-50% protein and is widely used as a high-quality animal feed supplement, supporting livestock nutrition in regions with limited protein sources.[48] Groundnut shells, comprising about 25-30% of the pod weight, are utilized as biomass fuel in boilers for energy generation or as mulch to suppress weeds and retain soil moisture in agricultural settings.[49] Haulms, the aboveground plant residues post-harvest, provide nutritious fodder for ruminants, valued for their palatability and contribution to dry-season feeding in mixed crop-livestock systems.[50] Beyond extraction byproducts, groundnut derivatives find applications in cosmetics and pharmaceuticals. Refined groundnut oil functions as an emollient in skincare products, enhancing skin conditioning due to its non-comedogenic properties and moisturizing effects.[51] In pharmaceuticals, arachis oil serves as a base for creams and ointments, as well as a laxative enema, leveraging its lubricating qualities to soften impacted feces.[52] Protein isolates derived from groundnut meal are incorporated into biodegradable plastics, forming films and packaging materials with improved mechanical strength and environmental degradability.[53] Groundnuts also play an environmental role in sustainable agriculture as a green manure and cover crop. As a legume, groundnut fixes atmospheric nitrogen through symbiotic rhizobia, enhancing soil fertility by adding 20-60 kg of nitrogen per hectare when incorporated into the soil, thereby reducing the need for synthetic fertilizers in crop rotations.[54] This practice improves soil structure, increases organic matter, and suppresses erosion, making groundnut an effective component in conservation tillage systems.[55]Nutritional profile and health aspects
Macronutrients and micronutrients
Groundnuts, also known as peanuts, provide a nutrient-dense profile rich in both macronutrients and micronutrients. Per 100 grams of raw kernels, they contain approximately 567 kcal of energy, with 25.8 grams of protein, 49.2 grams of total fat (predominantly monounsaturated fats such as oleic acid, comprising about 46% of the total fatty acids), 16.1 grams of carbohydrates, and 8.5 grams of dietary fiber.[56][57] Key micronutrients in raw groundnuts include vitamin E at 8.33 mg (providing over 50% of the daily value), niacin at 12 mg (about 75% of the daily value), folate at 240 μg (60% of the daily value), and magnesium at 168 mg (40% of the daily value).[56] Additionally, groundnuts are a source of antioxidants such as resveratrol, a stilbenoid compound present in concentrations ranging from 0.03 to 0.32 μg/g in raw and processed forms.[58][59]| Nutrient | Amount per 100g Raw Kernels | % Daily Value* |
|---|---|---|
| Energy | 567 kcal | 28% |
| Protein | 25.8 g | 52% |
| Total Fat | 49.2 g | 63% (mostly monounsaturated) |
| Carbohydrates | 16.1 g | 6% |
| Dietary Fiber | 8.5 g | 30% |
| Vitamin E | 8.33 mg | 56% |
| Niacin | 12 mg | 75% |
| Folate | 240 μg | 60% |
| Magnesium | 168 mg | 40% |