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12(1): Medicinal and poisonous plants 1

Oxalis corniculata L.

Sp. pl. 1: 435 (1753).

OXALIDACEAE

2n = 24, 28, 44, 48

Oxalis repens Thunb. (1781), Oxalis javanica Blume (1825).

Indian sorrel, creeping wood-sorrel, procumbent yellow sorrel (En). Indonesia: daun asem kecil (Sumatra), calingcing (Sundanese), semangnen (Javanese). Malaysia: sikap dada (Peninsular). Papua New Guinea: kokavu (Kami, Eastern Highlands), akler (New Britain). Philippines: taingan-daga (Tagalog), marasiksik (Iloko), daraisig (Bikol). Singapore: sikap dada. Burma (Myanmar): hmô-gyin. Cambodia: chantoe phnom kok. Laos: som ten kalm. Thailand: phak waen (central), som sangka (Chiang Mai), som din (Mae Hong Son). Vietnam: me d[aas]t, chua me ba ch[if]a, toan t[uw][ow]ng th[ar]o.

Oxalis consists of about 700 species and has its centres of diversity in South America and South Africa. Only a few species occur in South-East Asia; in Malesia there are 3 native species and 5 introduced ones, 4 of which have naturalized, sometimes becoming weeds. Oxalis corniculata is a cosmopolitan weed of unknown origin, although a southern European origin has been postulated. It occurs throughout South-East Asia, but is scarce in Peninsular Malaysia, Borneo and Sulawesi.

Oxalis corniculata is considered a good medicine against scurvy, e.g. in the Philippines, India and China. The juice of the leaves is used for cleansing wounds and to treat itch, burns, sores, insect and scorpion stings, and for removing warts. A poultice of the leaves relieves pain due to swellings. The leaves are taken as a good remedy in cases of intestinal complaints, and are applied externally to treat miliaria. A decoction of the leaves is sometimes used as a gargle against sore mouth and gums, and to treat cough, fever and dysentery. The whole plant is used as a diuretic and to treat opacity of the cornea. In Thailand, the aerial parts are used as an emmenagogue and to treat cough. In Korea, the entire plant is used in the treatment of dysentery, haemorrhoids and as an antidote. In China, it is considered to be cooling, emmenagogic, anthelmintic and lithotriptic. In Papua New Guinea and East Africa, the pounded plant is applied to remove ringworm. Oxalis corniculata is sometimes used to remove rust and ink stains, and to scour copper, due to the presence of oxalates (mainly potassium) and their ability to form metal complexes. The use as an antidote to mercury or arsenic poisoning is also sometimes reported. Small amounts of leaves have been added to food as a seasoning, but larger amounts can be toxic. Although it is usually a serious weed, it may sometimes serve as a valuable cover crop in preventing soil erosion in perennial crops such as tea and coconut.

Oxalis corniculata is only used locally and has no importance on the market.

Oxalis derives its acid taste from the presence of oxalates (mainly in the form of soluble potassium salt). Oxalates are toxic in high doses. They combine with serum calcium to form insoluble calcium oxalate. The reduction in available calcium leads to violent muscular stimulation with convulsions and collapse. In cases of poisoning, calcium oxalate crystals are also found in the renal tubulus; acute renal failure may occur from blockage of the renal tubuli. The principal manifestation of oxalate poisoning is anuria. In laboratory animals, the symptoms of acute poisoning are enlarged, pale kidneys, loss of control of fore or hind quarters and tetany.
The leaves contain 'BETA'-carotene, and the C-glycosyl flavonoids vitexin, isovitexin and vitexin-2''-O-'BETA'-D-glucoside. On extraction with chloroform-methanol young leaves yielded 1.5% lipids (on dry weight basis). These leaf lipids are a good source of essential fatty acids and also of 'BETA'-tocopherols.
Aqueous leaf and root extracts have brought about significant reduction in seedling growth of e.g. wheat; the allelopathic activity is due to oxalic acid and fumaric acid. Tests in India showed that powdery mildew (caused by Phyllactinia corylea) and leaf rust (caused by Pseudocercospora mori) of mulberry (Morus spp.) were minimized by a 10% alcoholic water extract of fresh Oxalis corniculata plants. The extract also has insecticidal property.

A perennial, creeping or ascending small herb, with stems up to 50 cm long, rooting at the nodes; main root fibrous, in old plants sometimes developing into a thickened and woody rootstock; stems several from the main root, branching, puberulous. Leaves alternate, digitately 3-foliolate, petiole 1-5.5(-10) cm long, stipules small, up to 3 mm long; leaflets broadly obcordate to elliptical-obcordate, 4-20(-25) mm x 5-18(-25) mm, pubescent to sericeous beneath. Inflorescence cymose to pseudo-umbellate, pedunculate, 1-6(-8)-flowered; bracts 2-several, subopposite to whorled. Flowers bisexual, actinomorphic, 5-merous, usually homostylous with mid-styled form, rarely with long-styled form; pedicel up to 20 mm long, articulate at base and beneath the calyx; sepals imbricate, short connate at base, lanceolate, 2-6 mm x 0.5-2 mm, sparsely puberulous to sericeous; petals contorted, coherent above the claw, spatulate-oblong to spatulate-lanceolate, 3.5-10 mm x 1-7 mm, glabrous, yellow; stamens 10, with 5 longer and 5 shorter filaments connate at base, the shorter rarely with rudimentary anthers; ovary superior, 5-celled, styles 5, free, with small, cylindrical stigmas. Fruit a linear-cylindrical, sometimes ellipsoid, pentagonal capsule, 9-20(-24) mm x 2-4 mm, pubescent, green, opening by longitudinal loculicidal slits, many-seeded. Seeds flattened-ovoid, about 1 mm long, red-brown; testa with about 3 regular rows of 7-10 transversally connected rows of ridges; aril bivalved, membranous, white. Seedling with epigeal germination; cotyledons leafy, with cuneate base and rounded apex, glabrous; hypocotyl elongated, epicotyl absent.

In the evening the leaves of Oxalis corniculata fold down around the leaf stalk. Plants usually flower throughout the year in the tropics. It is reported to be a facultative self-pollinator. Plants may produce seed about 20 weeks after germination. The seeds are forcefully ejected from the fruit in dry weather by the elastic aril.

Some other Oxalis species are occasionally used for medicinal purposes, e.g. Oxalis magellanica J.G. Forster to aid conception in Papua New Guinea. Oxalis corymbosa DC. is also used medicinally, e.g. in Vietnam and India, but its main use is as a culinary herb.

Oxalis corniculata is a common weed in gardens, fields, grassland, in roadsides, on river banks and on walls, up to 3000 m altitude. It thrives best in warm, moist, freely drained and fertile soils with a pH of 3.5-6.5. It is commonly found in vegetables, groundnut, maize, soya bean and root crops in the Philippines, and is a weed in tea and rice in Indonesia. In temperate regions, Oxalis corniculata is mainly a problem in greenhouses, but sometimes escapes to establish locally outdoor populations. Its prostrate habit helps to protect it from being mowed in lawns.

A single plant of Oxalis corniculata may produce up to 26 000 seeds. Seed viability is approximately 95%, and seeds require low levels of light for germination. When stored under dry conditions, they may retain germination rate of over 80% until 8 months, and of 50% after 15 months.

Oxalis corniculata may act as a host for several pathogenic organisms, e.g. Botrytis, Fusarium, Microsphaera and Puccinia species, and for organisms feeding on crops, e.g. Meloidogyne nematodes and insects of the genera Ovarus and Argynnis.

Oxalis corniculata is common around houses and on agricultural land. It is collected whenever the need arises.

Oxalis corniculata is extremely widespread and occurs in anthropogenic habitats, making it not at risk of genetic erosion. There is even much effort to eradicate it as a noxious weed, but it seems well able to survive since it is often resistant to hormone-type herbicides.

Since hardly any information is available on the pharmacological activity of Oxalis corniculata and its compounds it is impossible to indicate its future importance as a medicinal plant in modern phytotherapy.

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R.C.K. Chung

Chung, R.C.K., 1999. Oxalis corniculata L.. In: de Padua, L.S., Bunyapraphatsara, N. and Lemmens, R.H.M.J. (Editors): Plant Resources of South-East Asia No 12(1): Medicinal and poisonous plants 1. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea