Arachis hypogaea L.
Family
Leguminosae
Synonyms
None
Vernacular Names
| Malaysia | Kacang China, kacang Jawa, kacang goring. |
| English | Groundnut, peanut. |
| Indonesia | Kacang tanah, kacang Jawa, kacang Manila. |
| Papua New Guinea | Galip bilong giraun, kasang. |
| Philippines | Mani, batung-China. |
| Cambodia | Sânndaèk dèi. |
| Laos | Thwàx din, thwàx ho. |
| Thailand | Thua lisong, thua din. |
| Vietnam | Dâu phong, lac. |
| French | Arachide. |
Geographical Distributions
Arachis hypogaea originated in the southern Bolivia and northwestern Argentina area of South America. It is believed that the Portuguese took them from Brazil to West Africa and then to southwest India in the 16th century. Africa is now regarded as a secondary centre of diversity. At the same time also the Spaniards introduced A. hypogaea from Mexico to the western Pacific from where they spread to China, Indonesia and Madagascar. The Dutch also probably took A. hypogaea from Brazil to Indonesia in the middle of the 17th century. The groundnuts are thought to have been introduced to the USA on slave ships from Africa, although they may have been introduced directly from the Caribbean Islands. A. hypogaea is now grown in most tropical, subtropical and temperate countries between 40°N and 40°S latitude. They are most important in Africa, Asia, North America and South America. In Asia, A. hypogaea is a major crop in India, China, Indonesia, Burma, Thailand and Vietnam.
Description
A. hypogaea is a monoecious, prostrate to erect annual herb and it is usually 15-70 cm high. The root system consists of a well developed taproot with many lateral roots and able to penetrate to depths in excess of 2 m. Root hair is absent while the nitrogen-fixing nodules are present.
The main stem or central axis develops from the epicotyl and bears a cotyledon at each of the first two nodes. It has dimorphic branching with vegetative and contracted reproductive branches. All vegetative branches are characterised by the presence of scale leaves that called cataphylls and subtending the first two nodes of the branch. The secondary and tertiary vegetative branches can develop from the primary vegetative branches.
The leaves on the central stem are spirally arranged in a 2/5 phyllotaxy while on the primary vegetative branches and the arrangement is distichous. The leaves are 4-foliolate and measuring 3-7 cm x 2-3 cm with two opposite pairs of obovate leaflets. The petiole is 3-7 cm long. The pulvini is at the base of the petiole and at the base of each leaflet cause characteristic night movements in which the petiole folds downwards and the leaflets fold upwards until they are touch.
The contracted reproductive branches or inflorescences are formed singly at both cataphyllar and ordinary leaf axils on vegetative branches and, in some forms at the higher nodes on the central stem. Each inflorescence bears 2-5 flowers. The short (axillary) branches develop in the axils of simple bracts which occur along the central axis of the inflorescence. These axillary branches of the inflorescence terminate after the production of one leaf and in the axil of which the flower is borne. An inflorescence never occurs in the same leaf axil as a vegetative branch. The flowers are sessile, consist of 4-6 cm long tubular hypanthium (fused lower parts of calyx, petal and staminal tube), at the top of which are borne expanded lobes of the 5 sepals and petals (pale yellow through to orange-red), and 10 short filaments with anthers.
The superior ovary of single sessile carpel is with 2-6 ovules and situated at the base of the hypanthium tube. The style is free within the tube and ends in a club-shaped stigma among the anthers. After fertilisation, a stalk-like structure called ‘peg’ or gynophore elongates where an intercalary meristem is at the base of the ovary. The peg curves to grow down towards the soil and carry the ovary at its tip which becomes hardened into a protective cap as the peg enters the soil. The length of the peg depends on the initial distance of the flower from the soil, but if this is more than 15 cm long, it usually fails to reach the ground and the tip dies. When the peg has penetrated the soil to a depth of 2-7 cm, it turns horizontal and fruit development begins as the tip swells rapidly.
The mature fruits (pods) are cylindrical, measuring 1-8 cm x 0.5-2 cm and contain 1-6 seeds. The pod surface, or pericarp, may be constricted to varying degrees between the seeds and reticulated because of the presence of veins in the hardened mesocarp.
The mature seeds, or kernels are cylindrical to ovoid and measuring 1-2 cm x 0.5-1 cm. Each seed is enclosed in a thin papery testa with colours that ranging from white to pink, red, purple, tan and shades of brown. Each seed has two large cotyledons where an epicotyl is with leaf and bud primordia, a hypocotyl and the primary root. Upon epigeal germination, the primary root elongates rapidly which reach 10-12 cm long before the lateral roots appear. As growth proceeds, the outer layer of the primary root of a seedling is sloughed off so that the root hairs do not form.
Ecology / Cultivation
A. hypogaea is grown between 40°N and 40°S latitudes in warm tropical and subtropical environments and in temperate humid climates with sufficiently long warm summers. Optimum means a daily temperature for growth is around 30°C, while growth ceases at about 15°C. The phenology of A. hypogaea is determined primarily by temperature, with cool temperatures delaying flowering.
In controlled environments, photoperiod has been shown to influence the proportion of flowers producing pods and assimilate distribution between vegetative and reproductive structures (harvest index) in some cultivars. Generally, long photoperiods (greater than 14 hrs) increase the vegetative growth and short photoperiods (less than 10 hrs) increase the reproduction growth. However, the significance of these effects in crop communities in the tropics and subtropics has yet to be established. Between 500 and 600 mm of water reasonably well distributed through the growing season will enable satisfactory groundnut production. Nevertheless, A. hypogaea is a drought tolerant species and able to withstand high internal water deficits, although yield reductions will generally result. Because pods are developed underground and must be recovered at harvest, friable well drained soils are preferred, although adequate plant growth and development will occur on heavier clay soils. For optimum growth, the soil pH should be in the range of 5.5-6.5, although Spanish types tolerate more acid conditions (to pH 4.5) and some cultivars grow well in alkaline soils to pH 8.5.
Line Drawing / Photograph
References
- Plant Resources of South-East Asia No. 1: Pulses.
