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Tetragonia tetragonioides (Pall.) Kuntze

Protologue
Revis. gen. pl. 1: 264 (1891).
Family
Aizoaceae
Chromosome number
2n = 32
Synonyms
Demidovia tetragonioides Pall. (1781), Tetragonia expansa Murray (1783).
Vernacular names
New Zealand spinach, warrigal cabbage (En). Tétragone cornue, épinard de Nouvelle-Zélande, épinard d’été (Fr). Espinafre de Nova Zelândia (Po).
Origin and geographic distribution
New Zealand spinach was already a popular vegetable in New Zealand, Australia and the Pacific Islands in the 18th century. It occurs naturally in coastal areas in this region and also in Japan, China and Taiwan. Perhaps it is native to New Zealand, and has naturalized from cultivation elsewhere. Since Captain Cook’s voyages it is known as an antiscorbutic plant. It was introduced in Europe and America in the late 18th century where it is a fairly common summer vegetable in home gardens, grown as a substitute for ordinary spinach (Spinacia oleracea L.). Yet it is seldom grown commercially, the reason being that the culinary quality is less appreciated than spinach and that it cannot compete with the latter in yield and ease of cultivation, the recalcitrant seed being the main handicap. In many subtropical regions and highland areas in the tropics it is locally grown in home gardens and sometimes for market production. In Africa it has been recorded from Senegal, and from eastern Africa from Somalia to South Africa and Madagascar, but it probably occurs in many other countries.
Uses
New Zealand spinach is eaten cooked as a green leafy vegetable. It can be used in many dishes, like amaranth, spinach or other leafy vegetables with a neutral soft taste. Yet it has a distinctive slightly bitter taste. In the United States the tender tips are also eaten raw in salads.
Production and international trade
New Zealand spinach has never become an important commercial vegetable due to its labour-intensive harvest and the difficult seed germination. It is grown mainly as a small-scale home garden vegetable, and production data are not available. In many countries in South-East Asia it is occasionally grown as a market vegetable, but in Africa it is rarely found at the market.
Properties
The composition of New Zealand spinach per 100 g edible portion (product as purchased less 20% waste) is: water 94 g, energy 59 kJ (14 kcal), protein 1.5 g, fat 0.2 g, carbohydrate 2.5 g, Ca 58 mg, P 28 mg, Fe 0.8 mg, vitamin A 4400 IU, thiamin 0.04 mg, riboflavin 0.13 mg, niacin 0.50 mg, folate 15 μg, ascorbic acid 30 mg (USDA, 2002). The nutritional value is comparable to other medium green leafy vegetables. Most Ca is present as oxalates and not available to the human body. Consumption as a raw vegetable has been discouraged because of a high saponin content.
Whole Tetragonia tetragonioides plants showed distinct anti-ulcerogenic activity in tests with mice. The active principles were determined as sterylglucosides and cerebrosides.
Adulterations and substitutes
In cooking New Zealand spinach may be replaced by other green leafy vegetables with a mild neutral taste, such as Ceylon spinach, amaranth, spinach and Swiss chard.
Description
Fleshy annual herb, rather dark green but covered all over with minute, shining, white papillae, strongly branched, with trailing-ascending stems up to 1 m long, erect when young, terete or slightly angular. Leaves succulent, arranged spirally, simple, without stipules; petiole 0.5–2.5 cm long; blade ovate-rhomboid-triangular, 1.5–11 cm × 1–7.5 cm, entire, dark green above, pale green beneath, dull on both sides. Flowers axillary, solitary or 2–3 together, bisexual, yellowish-green, inconspicuous; perianth-tube turbinate, 1.5–2 mm long during anthesis, with (3–)4(–5) unequal segments 2–3 mm long, under each segment with a short hornlet, enlarging after anthesis; stamens 4–22, filaments yellow; ovary semi-inferior, (2–)5–8(–10)-celled, styles as many as cells. Fruit a conical, obconical or globular drupe 2.5–12.5 mm long, dry and indehiscent, 4–10-seeded, surrounded by the perianth tube, with (3–)4(–5) horns. Seeds subreniform.
Other botanical information
In Africa, New Zealand spinach does not occur in the wild, although it has escaped from cultivation here and there. No cultivars have been described. The seed (in fact whole fruits containing several true seeds) is traded under the species name without cultivar names. Small morphological differences in leaf shape between accessions from different origin can be observed.
Growth and development
Usually the dry, hard fruits are sown. They germinate erratically, taking from 2 weeks to more than 3 months, or they stay dormant. A fruit sometimes results in one but mostly in more than one plantlet. The plant flowers and fruits readily and continuously, with no apparent negative effects on growth. New Zealand spinach is predominantly self-pollinated, but cross-pollination may occur. The fruits fall on the ground on ripening, thus reseeding itself. After germination, initial plant growth is slow with the development of an erect stem, but after 2–3 weeks growth accelerates and lateral branches are formed. Harvesting the young tips stimulates branching; the leaves on the lateral branches are smaller than the first leaves. Flowering starts after about 6 weeks, but the growth of side branches continues. After approximately 4 months plants start showing senescence and some months later they will die. However, with good care it is possible for the crop to persist for over one year, becoming a short-lived perennial.
Ecology
New Zealand spinach is a xerophyte, capable of enduring long periods of drought. The succulent leaves do not wilt rapidly. In the tropics New Zealand spinach is more suitable for highland regions, at elevations above 1000 m, but with good care it can also be grown in the lowlands. It likes moderately high temperatures of 15–30°C and does not tolerate freezing. New Zealand spinach is not sensitive to day length. A fertile, sandy, well-drained soil gives the best results. It is salt tolerant, but the leaves will be of poor quality.
Management
Manure and/or fertilizer should be amply supplied to obtain rapid, tender growth. A nitrogen fertilizer is advantageous as a side dressing to stimulate regrowth after harvesting. A produce of 30 t/ha of harvested shoots contains approximately 60 kg N, 15 kg P2O5 and 105 kg K2O; the total recommended fertilizer application per ha is 100 kg N, 25 kg P2O5 and 150 kg K2O. Once fully developed, one plant easily covers 1 m2 of ground surface. Mulching is not needed. Once fully established, the crop competes well with weeds, making weeding unnecessary. Although drought resistant, it is necessary to irrigate under dry conditions, giving at least 6 mm per day for a good yield of tender tops. When growth and yield become unsatisfactory, the mat of old plants may be pulled up, and the young plants which are developing underneath from fallen fruits may be used for a new crop.
Propagation and planting
New Zealand spinach is grown from fruits, which are easily obtained, even under tropical conditions. The fruits are very hard coated and can be kept for years without loss of viability. The weight of 1000 fruits is 65–100 g. For planting one ha, 5–15 kg of fruits are used. Before sowing they should preferably be soaked in water for a day to soften the coat and help faster germination. The fruits are covered with 1–4 cm soil. Seedlings are usually raised in nurseries and transplanted when they have 6–7 leaves into permanent beds at distances of 30–50 cm in the row and 100 cm between the rows. Soaked fruits can also be sown directly in the field. Propagation by stem cuttings is not practised. Because initial growth is slow, a young New Zealand spinach crop can be planted in alternating rows with another quick-maturing vegetable.
Diseases and pests
New Zealand spinach is little affected by diseases and pests. Rot of the prostrate stems may occur, but this is insignificant on sandy soils. Old plants may degenerate due to virus infestation. Leaf hoppers, snails and aphids are sometimes a bit troublesome. No serious soilborne diseases are known, except root-knot nematodes. These are controlled by crop rotation, e.g. with amaranth or with maize. Liberal gifts of organic fertilizer also reduce the nematode population.
Harvesting
When the central stem and the branches have grown to a height and length of over 30 cm, 6–8 weeks after germination, tops of 15–20 cm may be cut or handpicked for the first harvest. As the plant spreads over the soil, harvesting of new shoots by handpicking may continue at weekly intervals over a period of several months. When regularly cut back, the plant may persist in the tropics as a short-lived perennial. This is common in home gardens, whereas market gardeners remove the crop after some months when the yield and quality have become inferior. Regular harvesting with short intervals, e.g. once per week or per 2 weeks, is recommended to promote growth of new shoots. Older leaves including stems with fruits must be avoided for consumption as they become bitter and fibrous.
Yield
The yield of the first harvest amounts up to 1 kg per m2. With continuous harvesting over a period of 3–4 months, a total yield of about 3 kg/m2 may be obtained.
Handling after harvest
The leaves do not store for more than a day at ambient temperatures. They should be consumed soon after harvest or put in a cool room.
Genetic resources
No germplasm collections have been recorded.
Breeding
Genetic improvement of the crop has not been undertaken. Many seed companies in Western countries sell fruits (‘seed’) of New Zealand spinach. Various accessions show a slight variation mainly in leaf shape.
Prospects
New Zealand spinach is easy to grow, high yielding and nutritious. It is an ideal vegetable for home gardens. A few plants are sufficient for a regular supply. It is drought resistant, salt tolerant, and hardly affected by pests and diseases. It deserves more attention, especially in the African highland areas. Research could concentrate on genetic variation with possibilities for breeding, and on seed technology to solve the germination problem.
Major references
• Fritz, D., Stolz, W., Venter, F., Weichmann, J. & Wonneberger, C., 1989. Gemüsebau. 9th Revised edition. Ulmer, Stuttgart, Germany. 379 pp.
• Gonçalves, M.L., 1978. Tetragoniaceae. In: Launert, E. (Editor). Flora Zambesiaca. Volume 4. Flora Zambesiaca Managing Committee, London, United Kingdom. pp. 553–555.
• Halpin, A.M., 1978. Unusual vegetables. Rodale Press, Kutztown, United States. 443 pp.
• Jeffrey, C., 1961. Aizoaceae (including Molluginaceae and Tetragoniaceae). In: Hubbard, O.B.E. & Milne-Redhead, E. (Editors). Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 37 pp.
• Marais, W., 1993. Aizoacées. In: Bosser, J., Cadet, T., Guého, J. & Marais, W. (Editors). Flore des Mascareignes. Familles 90–106. The Sugar Industry Research Institute, Mauritius, l’Institut Français de Recherche Scientifique pour le Développement en Coopération (ORSTOM), Paris, France & Royal Botanic Gardens, Kew, United Kingdom. 13 pp.
• Okuyama, E. & Yamazaki, M., 1983. The principles of Tetragonia tetragonoides having anti- ulcerogenic activity. 2. Isolation and structure of cerebrosides. Chemical and Pharmaceutical Bulletin 31(7): 2209–2219.
• Rubatzky, V.E. & Yamaguchi, M., 1997. World vegetables: principles, production and nutritive values. 2nd Edition. Chapman & Hall, New York, United States. 843 pp.
• Siemonsma, J.S., 1993. Tetragonia tetragonioides (Pallas) O. Kuntze. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 269–271.
• Tindall, H.D., 1983. Vegetables in the tropics. Macmillan Press, London, United Kingdom. 533 pp.
Other references
• Gilbert, M.G., 1993. Aizoaceae. In: Thulin, M. (Editor). Flora of Somalia. Volume 1. Pteridophyta; Gymnospermae; Angiospermae (Annonaceae-Fabaceae). Royal Botanic Gardens, Kew, United Kingdom. pp. 111–117.
• USDA, 2002. USDA nutrient database for standard reference, release 15. [Internet] U.S. Department of Agriculture, Beltsville Human Nutrition Research Center, Beltsville Md, United States. http://www.nal.usda.gov/fnic/foodcomp. Accessed June 2003.
Sources of illustration
• Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. 525 pp.
• Siemonsma, J.S., 1993. Tetragonia tetragonioides (Pallas) O. Kuntze. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 269–271.
Author(s)
G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
Based on PROSEA 8: ‘Vegetables’.

Editors
G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
O.A. Denton
National Horticultural Research Institute, P.M.B. 5432, Idi-Ishin, Ibadan, Nigeria
Associate Editors
C.-M. Messiaen
Bat. B 3, Résidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
R.R. Schippers
De Boeier 7, 3742 GD Baarn, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Illustrator
Achmad Satiri Nurhaman
PROSEA Network Office, P.O. Box 332, Bogor 16122, Indonesia
Photo Editor
E. Boer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Grubben, G.J.H., 2004. Tetragonia tetragonioides (Pall.) Kuntze In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
Distribution Map planted


1, plant habit; 2, flowering and fruiting shoot; 3, flower; 4, fruit.
Redrawn and adapted by Achmad Satiri Nurhaman



close up of plant


close up of shoots