Oxalis (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Oxalis corymbosa: 1, habit flowering plant; 2, leaf; 3, scale of bulbil; 4, flower (top view), 5, flower (side view)

Oxalis L.

Protologue: Sp. pl.: 433 (1753); Gen. pl., ed. 5: 198 (1754).

Family: Oxalidaceae

Chromosome number: x = unknown; 2n = 12, 24 (O. barrelieri); 2n = 14, 22, 28 (O. corymbosa); 2n = 24, 26, 46 (O. latifolia)

Major species and synonyms

- Oxalis barrelieri L., Sp. pl., ed. 2: 624 (1763), synonyms: O. sepium A. St. Hil. (1825), O. sepium A. St. Hil. var. picta Progel (1877);

- Oxalis corymbosa DC., Prodr. 1: 696 (1824), synonyms: O. martiana Zucc. (1825), O. violacea auct., non L. (1753); O. debilis Kunth var. corymbosa (DC.) Lourteig (1980);

- Oxalis latifolia Kunth, Nov. gen. sp. 5: 184, t. 467 (1822), synonym: O. intermedia A. Rich. (1841).

Vernacular names

General

• Oxalis, sorrel, shamrock (En)

• Oxalis, oxalide (Fr)

• Indonesia: calingcing (Sundanese)

O. barrelieri

• Indonesia: belimbing tanah (Indonesian), calingcing (Sundanese)

O. corymbosa

• Pink wood-sorrel (En)

• Indonesia: kembang gelas (Indonesian), calingcing beureum (Sundanese), asam puja (West Sumatra)

• Vietnam: chua me dất hoa dỏ

O. latifolia

• Purple garden oxalis, fishtail oxalis (En)

• Indonesia: calingcing (Sundanese)

Origin and geographic distribution

Oxalis is a cosmopolitan genus of more than 800 species, but major centres of diversity are in South America and South Africa.

- O. barrelieri is native to tropical South America, but has naturalized in many areas. It was first observed in Java in 1888. In South-East Asia it is common in Indonesia (Sumatra, Bangka, Java, Irian Jaya), Peninsular Malaysia, and Papua New Guinea.

- O. corymbosa is native to tropical South America, but has naturalized in many areas and is a common pot-plant. It was introduced into Java from Sydney before 1848. In South-East Asia it is common but only occasionally cultivated in Indonesia (Java, West Sumatra), Peninsular Malaysia and the Philippines (Luzon).

- O. latifolia is native to Central and tropical South America. It has naturalized in many areas. In South-East Asia it occurs in Indonesia (Java), where it was already abundant before 1924.

Uses

In Indonesia, the leaves of Oxalis are used in salads, in particular for their sour or slightly acid taste. They are sometimes used as a substitute for tamarind. When consumed in large quantities, they are toxic.

Oxalis contains many ornamental plants. Among the "culinary herb” species it is especially O. corymbosa which has ornamental value; it is a common pot-plant in e.g. California. Some cultivars are marketed, such as "Aureo-reticulata” with yellow-veined leaves. There are also double-flowered forms. Medicinal use of O. corymbosa has been reported from Zaire (febrifuge and anti-malaria) and India.

It is important to realize, however, that Oxalis, especially the ones with underground bulbils, are potentially troublesome weeds difficult to eradicate.

Production and international trade

As culinary herbs Oxalis spp. are only used locally and have no importance on the market in South-East Asia.

Properties

Many Oxalis spp. accumulate large amounts of oxalic acid in water-soluble form. Excess consumption should be avoided.

Adulterations and substitutes

It seems that Oxalis is used mainly when the many other sources of "asam” (sour leaves, sour fruits) are not readily at hand.

Description

• Annual or perennial herbs or subshrubs, some stemless with rhizomes, bulbs and tuberous roots.
• Leaves alternate, apparently cauline, subopposite or pseudoverticillate, digitately or pinnately 3(-4)-foliolate; stipules, when present, adnate to the base of the petiole.
• Inflorescence axillary, cymose to umbellate or flowers solitary; bracts small, bracteoles 2.
• Pedicel articulate; calyx 5-partite; petals 5, connate near the middle; stamens 10, connate at base, 5 outer ones opposite the petals and shorter than the 5 inner ones opposite the sepals; pistil heterostylous, carpels 1-15-ovuled, styles 5, stigmas capitate.
• Fruit a capsule, loculicidally dehiscent, each carpel with 1-15 seeds.
• Seed with crustaceous testa, longitudinally zig-zag ribbed, transversely striate or sculptured, densely verrucate, the external integument fleshy, arilliform, breaking elastically and ejecting the ripe seed.

O. barrelieri

• Erect, branched herb or shrub, up to 1.5 m tall, pubescent, without bulbs or rhizomes.
• Leaves subopposite, pinnately 3-foliolate, without stipules; petiole 2-9 cm long, canaliculate, ascendent; petiolule fleshy, about 1 mm long; leaflet elliptical to oblong, 1-5.5 cm × 0.5-2.5 cm, terminal one largest, base cuneate to emarginate, margin ciliate (especially at base), apex obtuse to rounded, discolorous, glaucous above.
• Inflorescence cymose, up to 11(-30)-flowered; peduncle up to 6.5 cm long, bifid with branches up to 3 cm long, pubescent; bracts opposite the pedicels, pilose.
• Pedicel up to 3 mm long with appressed bracteoles; sepals ovate-lanceolate, 2-4 mm × 0.5-1.5 mm, light green, sometimes reddish veined; petals obovate-lanceolate, 6-9 mm × 2-2.5 mm, pink but lower half greenish with yellow spots, rolling inwards after anthesis; outer stamens up to 2 mm long, inner ones up to 3 mm long bearing a dorsal tooth; pistil 3.5-4 mm long, carpels 3-4-ovuled, styles 1-1.5 mm long, pubescent.
• Capsule ovoid, 5-10 mm × 3-5 mm, 5-angular, base and apex 5-lobed, glabrous.
• Seeds usually 3 per carpel, flattened-ovoid, about 1.5-2 mm × 1 mm, 8-ribbed in zig-zag, deeply transversely striate, brownish.

O. corymbosa

• Stemless herb, 10-45 cm tall, arising from an underground bulb with fibrous roots but sometimes with an obconical, up to 4 cm long and often rather thick, white taproot; bulb globose, ovoid or cylindrical, up to 1-2 cm long, 3 cm in diameter, composed of numerous densely clustered bulbils each covered by a number of 3-veined, brown, acuminate, ovate to oblong scales up to 2 cm × 0.6 cm.
• Leaves digitately 3-foliolate; petiole up to 30 cm long, sparsely to densely hairy; petiolules fleshy, up to 1 mm long, pilose; leaflets more or less equal, suborbicular-cordate to broadly obcordate, up to 4.5 cm × 6 cm, incision at apex up to 20% of the length, usually subglabrous above and appressed hairy beneath, with punctiform minute, translucid, orange or violaceous oxalate "crystals” scattered all over the surface, more densely along the margins.
• Inflorescence a bifid or twice bifid cyme with unequal branches, asymmetrical or umbelliform, 3-15-flowered; peduncle up to 45 cm long, similar to the petiole; bracts and bracteoles small with linear calli near the middle.
• Pedicel up to 2.5 cm long, articulate near the base; sepals linear to elliptical, 3.5-7 mm × 1-2 mm, at apex with 2 orange calli (dots or stripes); petals spatulate-oblong-lanceolate, 2-3 times the size of the sepals, pinkish, salmon or red-violet; outer stamens 2-4 mm long, inner ones 5-6 mm long; pistil 7.5 mm long, carpels 2-12-ovuled, styles of different lengths, 1-2 mm long, stigma subcapitate, bilobed.
• Capsule cylindrical, up to 17 mm long, glabrous, carpels 3-10-seeded, but fruiting is rare.
• Seed flattened ovoid, 12-ribbed in zig-zag with 12 transversal striae, brownish.

O. latifolia

• Stemless herb, 10-30 cm tall, arising from a bulbous base with often a whitish, thick, vertical taproot about 5 cm long and fibrous branches; bulb ovoid to globose, up to 5 cm × 2 cm, with many brown, elliptical, 3-many-veined scales up to 5 cm × 2 cm, inner scales smallest and fleshy; from the base of the bulb arise numerous, more or less erect stolons 1-7 cm long, each ending in an ovoid bulbil about 1 cm long.
• Leaves digitately 3-foliolate; petiole up to 20 cm long, subglabrous; petiolules fleshy, about 1 mm long, pilose; leaflets subequal, broadly obtriangular, 1-7.5 cm × 2-8.5 cm, shallowly but broadly notched and often with 2 orange calli in the notch, margin finely ciliate.
• Inflorescence an umbelliform cyme, up to 30 cm long, loosely 5-20-flowered; peduncle 10-25 cm long; bracts and bracteoles small.
• Pedicel filiform, up to 2 cm long; sepals linear-elliptical to oblong, 3-6 mm × 0.5-3 mm, indistinctly 3-5-veined, with 2 orange apical calli about 1 mm long; petals narrowly obtriangular, 10-20 mm × 3-8 mm, truncate, red-purplish with greenish base; stamens puberulous, outer ones about 3 mm long, inner ones 4 mm long and bearing a small tooth near the middle; pistil up to 5.5 mm long, carpels 4-8-ovuled, styles about 1 mm long (only short ones), stigmas bifid.
• Capsule cylindrical, 4-8.5 mm long, glabrous, carpels 4-8-seeded but fruiting is rare.
• Seed flattened ellipsoidal, 1 mm long, 8-9-ribbed in zig-zag with 12-13 transversal striae, brownish.

Growth and development

Three main phases in the growth of O. latifolia raised from bulbs can be distinguished. The establishment phase (weeks 1-5) is characterized by slow gain in dry weight in absolute terms, but a high relative growth rate (RGR). During the reproductive phase (weeks 6-12) stolons grow off the parental bulb and initiate bulbils at the apices; some primary bulbils support secondary bulbils. The RGR, net assimilation rate (NAR) and leaf area index (LAI) decrease. They decrease further during the senescence phase (week 13 and onwards).

The seed-bearing Oxalis such as O. barrelieri have a peculiar ejaculative aril originally enveloping the entire seed which at maturity is shot some distance away. The non-fruiting species such as O. corymbosa and O. latifolia perpetuate tenaciously through their bulbils. O. latifolia is apparently functionally heterostylous; it occurs in the short-styled form only with probable loss of the mid- and long-styled forms. It has never been observed with fruit in South-East Asia. O. corymbosa occurring in short-styled and mid-styled forms but with probable loss of the long-styled form, does not fruit easily either.

Other botanical information

In South-East Asia 8 Oxalis species occur, 3 native (O. acetosella L. subsp. griffithii (Edgew. & Hook.f.) Hara, O. corniculata L., O. magellanica Forst.f.) and 5 introduced (O. barrelieri, O. corymbosa, O. fruticosa Raddi, O. latifolia and O. tetraphylla Cav.). Apart from the 3 species treated here as culinary herbs, O. corniculata is similarly used (Indonesia: "daun asam kecil”) but has greater importance as medicinal plant, whereas the others have some importance as ornamental plants.

The 3 Oxalis species dealt with here can easily be distinguished: O. barrelieri has a stem but no bulbs and bulbils and the leaves are pinnately 3-foliolate; O. corymbosa and O. latifolia are stemless with underground bulbs and bulbils and the leaves are digitately 3-foliolate; in O. corymbosa the bulbils are clustered and without stolons, in O. latifolia the bulbils appear at the end of stolons arising from the bulb.

Ecology

Oxalis is primarily found in anthropogenic habitats: in gardens, along roads, in hedges, fields, village groves, estates, along rivers, and in grassy locations with shade. O. barrelieri occurs from sea-level up to 1500 m altitude, O. corymbosa between 400-1500 m, and O. latifolia between 1100-1800 m.

In weed control studies, it has been observed that O. corymbosa grows best under heavy shade (50%); however, bulb or bulbil production is not affected by shade. Alfisols are preferred above Entisols, Inceptisols and Ultisols. Growth and reproduction are negatively affected at moisture conditions below field capacity. Acid soils are preferred and growth slows down with increasing pH.

Agronomy

O. barrelieri is propagated by seed, whereas O. corymbosa and O. latifolia are reproduced successfully by bulbils. Planting depth (1-25 cm) hardly affects the sprouting percentage of O. corymbosa bulbs, but increasing depth delays emergence and decreases number of leaves and number of daughter bulbs. Bulbs weigh between 0.1-2.5 g, sprouting being highest in the weight range of 0.2-2.0 g. Since Oxalis herbs are easily collected from the wild, they are rarely cultivated.

O. corymbosa and O. latifolia are sometimes affected by orange rust caused by Puccinia oxalidis, resulting in many lesions on the leaves. Both species have been reported as a host for root-knot nematodes (Meloidogyne arenaria in particular), whereas O. corymbosa is also affected by Meloidogyne javanica.

Genetic resources and breeding

The Oxalis herbs are widespread, and their occurrence in anthropogenic habitats makes them unlikely candidates for genetic erosion. There is even much effort to eradicate them as noxious weeds. There are no known breeding programmes.

Prospects

Since there is little information on Oxalis, it is difficult to judge its future importance as culinary herb. Because of restricted use it is best marketed to the consumer in small quantities, e.g. as living plants in small pots as is practised for parsley, leaf celery (celery herb) and chives in the western world.

Literature

• Choudhary, J.K. & Pathak, A.K., 1992. Studies on the biology of wood-sorrel (Oxalis corymbosa DC.). Journal of the Assam Science Society 34(1): 72-77.

• Everaarts, A.P., 1981. Weeds of vegetables in the highlands of Java. Horticultural Research Institute, Pasarminggu, Jakarta, Indonesia. pp. 58-61.

• Ishimine, Y. & Takaesu, Y., 1977. Physiological and ecological studies on Oxalis corymbosa DC., a perennial weed in upland fields. I. Relation between soil depth and bulb formation, germination and growth of the weed. Science Bulletin of the College of Agriculture, University of the Ryukyus 24: 611-619.

• Lourteig, A., 1980. Oxalidaceae. Oxalis. In: Flora of Panama. Part 4. Annals of the Missouri Botanical Garden 67: 835-849.

• Marshall, G. & Gitari, J.N., 1988. Studies on the growth and development of Oxalis latifolia. Annals of Applied Biology 112(1): 143-150.

• Veldkamp, J.F., 1970. Oxalidaceae. In: Smitinand, T. & Larsen, K. (Editors): Flora of Thailand. Volume 2, Part 1. The Forest Herbarium, Royal Forest Department, Bangkok, Thailand. pp. 16-23.

• Veldkamp, J.F., 1971. Oxalidaceae. In: van Steenis, C.G.G.J. (Editor): Flora Malesiana. Series 1, Volume 7, Part 1. Noordhoff International Publishing, Leiden, the Netherlands. pp. 151-178.

Sources of illustrations

Oxalis corymbosa: Everaarts, A.P., 1981. Weeds of vegetables in the highlands of Java. Horticultural Research Institute, Pasarminggu, Jakarta, Indonesia. Fig. 42, p. 58. Redrawn and adapted by P. Verheij-Hayes.

Authors

• R.C.K. Chung & S.S. Budi Rahayu