Rorippa (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Rorippa Scop.

Protologue: Fl. Carniol.: 520 (1760).

Family: Cruciferae

Chromosome number: x= 16; 2n= 32 (R. nasturtium-aquaticum)

Major species and synonyms

• Rorippa heterophylla (Blume) Williams, Fl. Trinidad & Tobago 1: 24 (1929), synonyms: Nasturtium heterophyllum Blume (1825), Rorippa dubia (Pers.) Hara (1955), Nasturtium indicum (L.) DC. sensu auct. mult.

• Rorippa nasturtium-aquaticum (L.) Hayek, Sched. Fl. Stir. Exs. 3-4: 22 (1905), synonyms: Sisymbrium nasturtium-aquaticum L. (1753), Nasturtium officinale R. Br. (1812), Rorippa officinalis (R. Br.) P. Royen (1982).

• Rorippa schlechteri (O.E. Schulz) P. Royen, Mt. Fl. New Guinea 3: 2031 (1982), synonym: Nasturtium schlechteri O.E. Schulz (1918).

Vernacular names

R. heterophylla

• Indonesia: sesawi langit, sesawi tanah (Sundanese), sudukan (Javanese)
• Philippines: lampaka (Ilocano), mustapa (Bisaya), amat (Ifugao)
• Laos: kaad h'oong
• Thailand: phakkat-nam
• Vietnam: lai hoàng.

R. nasturtium-aquaticum.

• Watercress (En)
• Cresson de fontaine (Fr)
• Indonesia: selada air, kenci
• Malaysia: selada air
• Papua New Guinea: wara karis
• Philippines: pakhoy (Ifugao)
• Cambodia: krèh-sông
• Laos: kaad fàlangx
• Vietnam: cải soong.

R. schlechteri.

• Highland cress (En)
• Papua New Guinea: ao.

Origin and geographic distribution

• R. heterophylla is indigenous to East Asia from Japan to Burma. It has been introduced into other tropical areas all over the world, including South-East Asia.

• R. nasturtium-aquaticum is native to Europe, western Asia and perhaps Ethiopia. It is cultivated and often naturalized in temperate and tropical highland areas throughout the world, including South-East Asia.

• R. schlechteri is endemic to Papua New Guinea where it is widely cultivated in the highlands.

Uses

Young shoots of all 3 species are usually consumed raw, but they can also be cooked as spinach or in soups. Watercress is sometimes merely used as a garnish or condiment. Used raw it imparts a peppery flavour. Medicinally, watercress was chiefly valued as an antiscorbutic in the past. Steeped in wine or prepared as a syrup, it is also used as a stimulant and laxative. The seeds of R. heterophylla are used to cure asthma.

Production and international trade

In South-East Asia Rorippa species are used and traded locally only. In some areas they are important market vegetables, e.g. in Java (Indonesia). No statistical data are available. Watercress is produced commercially in many western countries.

Properties

Watercress is a good source of vitamins and minerals. Per 100 g edible portion it contains: water 93 g, protein l.7-2.0 g, fat 0.2-0.3 g, carbohydrates 3.0-4.0 g, fibre 0.8-1.1 g, Ca 64-182 mg, P 27-46 mg, Fe 1.1-2.5 mg, vitamin A 2420 IU, vitamin B₁ 0.03-0.08 mg, vitamin B₂ 0.20-0.27 mg, vitamin C 45-50 mg. The energy value is 70-118 kJ/100 g. The plant yields a pungent, volatile oil, mainly containing phenyl-ethyl isothiocyanate.

Description

• Annual to perennial, prostrate to erect herb, with taproot, often easily rooting at the stem nodes.
• Leaves usually pinnatifid to pinnate.
• Inflorescences terminal racemes, without bracts in the 3 described species, with numerous small bisexual flowers; sepals 4, greenish, spreading; petals 4, yellow or white; stamens 6, distinctly tetradynamous; ovary cylindrical, with numerous ovules; style short with bifid stigma.
• Fruit a silique, two-valved, dehiscent.
• Seed numerous, ellipsoid to spheroid, 0.5-1.5 mm in diameter, yellowish to dark brown, finely sculptured.

R. heterophylla.

• Annual herb, 5-50 cm tall.
• Stem erect or ascending, one or more from the base, hardly branched.
• Leaves in a rosette and a few along the stem; lower ones narrowly obovate in outline, 1.5-8 cm long with 1-6 cm long petioles, undivided or lyrate-pinnatipartite with 1-3 pairs of small lateral lobes and a much larger terminal lobe; upper leaves rather few, undivided, narrowly ovate.
• Racemes 2-10 cm long; flowers with reduced or lacking petals, sepals green; pedicels straight, 2-8 mm long.
• Fruit linear, 14-25 mm × 0.7-1.3 mm, straight, less than 1.5 mm thick, with seed in one row only.
• Seed red-brown, rounded quadrangular, finely colliculate.

R. nasturtium-aquaticum.

• Perennial, much-branched, glabrous, aquatic herb, up to 1 m tall.
• Stem prostrate to ascending, juicy, hollow, usually rooting at the lower nodes.
• Leaves petiolate, auriculate, pinnate, oblong in outline, up to 10 cm long; lateral leaflets in 2-9 pairs, sessile, narrowly obovate, elliptical or nearly orbicular, entire to faintly dentate; terminal leaflet similar but larger.
• Racemes ca. 10 cm long; flowers with white petals; pedicels curved, ca. 1 cm long.
• Fruit broadly linear, 10-18 mm × 1.5-2.5 mm, more than 1.5 mm thick, often curved and torulose, 7-12 times as long as broad, with seeds arranged in two distinct rows.
• Seed shiny, red-brown, covered by a distinct reticulum.

R. schlechteri.

• Annual to short-lived perennial, 15-50 cm tall.
• Stem solitary, erect, hardly branched.
• Leaves indistinctly petiolate, auriculate in outline, 1.5-15 cm × 1-3.5 cm, lyrato-pinnate with 1-3 pairs of oblong lateral lobes, 0.2-1.5 cm × 0.1-0.6 cm, and a much larger elliptical-ovate terminal lobe.
• Racemes up to 15 cm long; flowers with yellow petals; pedicels curved, 3-10 mm long.
• Fruit inflated, semiglobose, 5-9 mm × 3-6 mm, more than 1.5 mm thick.
• Seed red-brown, minutely foreolate.

Growth and development

Rorippa species normally produce abundant seed and multiply rapidly. They are self compatible. R. nasturtium-aquaticum, however, seldom flowers in the tropics. For a vigorous growth it demands running water and then the plant becomes tender and sweet. If growth is slow it acquires a bitter taste. When established, the more the tops are harvested the better, as this induces branching. The plants can be harvested for several years, but diseases and weeds may necessitate new plantings more frequently.

Other botanical information

In the same distribution area of R. nasturtium-aquaticum (natural and naturalized), an allotetraploid species has spontaneously developed (2n= 64), named R. microphylla (Boenningh.) Hyl. (synonym: Nasturtium microphyllum Boenningh. ex Reichenb.). It has small leaves and is not cultivated. A spontaneous triploid hybrid (2n= 3x= 48), named R. × sterilis Airy Shaw (= R. microphylla × R. nasturtium-aquaticum), also occurs occasionally but is sterile and is rarely cultivated.

Ecology

R. heterophylla occurs on open, moist soils, often on cultivated land, at altitudes of 250-1500 m. R. nasturtium-aquaticum occurs naturally in and along running water, and also grows floating in shallow water. It is a long-day plant and very rarely flowers in the tropics. Watercress is most common at higher elevations (above 1000 m), and prefers sandy or gravelly soils, and is rather common in limestone areas, preferring slightly alkaline water (pH 6.5-7.5). It has become a troublesome weed in waterways in New Zealand, forming dense, large mats. R. schlechteri also prefers moist or marshy places, but it is cultivated mainly as an upland crop in Papua New Guinea. It is most common at higher elevations, up to 2600 m.

Agronomy

R. nasturtium-aquaticum is grown from seed (usually imported) or from cuttings. Cuttings root easily in wet sand and in water. Seedlings 8-10 cm tall or cuttings 10-15 cm long are planted out in beds which can be flooded. Paddy fields with not too heavy soils and continuous running water can be used. Plant spacing is usually 10-15 cm either way. Watercress has a high phosphate requirement and nitrate should be applied if the nutrient content of the water is low. Farmers in Indonesia apply urea after each harvest. The major disease is caused by a virus. If the crop is propagated by seed, it will grow virus-free. Other diseases are seldom of economic importance. Flea beetles (Phyllotreta spp.), aphids, and caterpillars may cause damage. Some of the pests can be controlled by flooding the crop. Farmers in Indonesia sometimes spray their crop with an insecticide against leaf-eating insects. This is a hazardous practice in view of water pollution and residues on the marketable product.

The first harvest can be taken 4-6 weeks after planting by cutting the 5-10 cm long top ends. This can be repeated at regular 4-6 week intervals for more than a year. Yields of 20 t/ha per cut are not uncommon. Watercress is very perishable and can only be stored for up to 3 days at 0°C and 100% relative humidity.

R. heterophylla and R. schlechteri flower and fruit abundantly in the tropics and are propagated by seed. In Papua New Guinea R. schlechteri is often planted on sweet potato mounds and harvested repeatedly, starting 4-6 weeks after planting, until the sweet potato canopy is closed. R. heterophylla is mainly gathered from the wild.

Genetic resources and breeding

There are no germplasm collections of Rorippa species. European seed catalogues list watercress, but there are no officially registered cultivars. Some breeding has been done in watercress, e.g. to create an artificial autotetraploid which has thicker and broader leaflets than the diploid but a slower growth rate. Breeding of higher yielding, disease-free cultivars of the 3 Rorippa species in South-East Asia seems very possible.

Prospects

The popularity of watercress (R. nasturtium-aquaticum) is still growing in South-East Asian countries like Indonesia and Papua New Guinea. However, its specific requirements as an aquatic plant needing a lot of clean running water, and its vegetative propagation in the tropics with problems of virus infection, may hamper its development into a major vegetable crop. A detailed comparison with the related "terrestrial" species (R. heterophylla and R. schlechteri) would seem to be useful.

Literature

• Fritz, D., Stolz, W., Venter, F., Weichmann, J. & Wonneberger, C., 1989. Gemüsebau [Vegetable growing]. 9th revised edition. Ulmer, Stuttgart, Germany. pp. 165-167.
• Howard, H.W., 1976. Watercress. In: Simmonds, N.W. (Editor): Evolution of crop plants. Longman, London, United Kingdom. pp. 62-64.
• Jonsell, B., 1988. Cruciferae. Rorippa. In: van Steenis, C.G.G.J. et al. (Editors), 1950- . Flora Malesiana. Series 1. Vol. 10. Kluwer Academic Publishers, Dordrecht, the Netherlands. pp. 555-560.
• Powell, J.M., 1982. Traditional vegetables in Papua New Guinea: retrospect and prospect. In: Proceedings of the Second Papua New Guinea Food Crops Conference, July 14-18, 1980, Goroka. Department of Primary Industry, Port Moresby, Papua New Guinea. pp. 64-77.
• Soedirdjoatmodjo, M.D.S., 1986. Bertanam sayuran daun [Growing leafy vegetables]. Karya Bani, Jakarta, Indonesia. pp. 121-124.
• Tindall, H.D., 1983. Vegetables in the tropics. MacMillan, London, United Kingdom. pp. 131-133.

Authors

• M. Rahmansyah