Tetragonia tetragonioides (PROSEA)
Tetragonia tetragonioides (Pallas) O. Kuntze
- Protologue: Rev. Gen.: 264 (1891).
- Family: Aizoaceae
- Chromosome number: 2n= 32
- Demidovia tetragonioides Pallas (1781),
- Tetragonia expansa Murrey (1783).
- New Zealand spinach, warrigal cabbage (En)
- Tétragone cornue, épinard d'été (Fr)
- Indonesia: kabak
- Malaysia: kabak
- Philippines: ispinaka (Tagalog)
- Vietnam: dền tây, giền tây.
Origin and geographic distribution
T. tetragonioides was discovered during Captain Cook's voyages as a good pot herb and antiscorbutic plant of the Southern Hemisphere. It occurs wild in the coastal regions of Australia, Tasmania, New Zealand, the Pacific Islands, Japan, China and Taiwan. It was successfully tried out as a vegetable in Europe in the early 19th Century and has been introduced into most temperate and subtropical regions. In South-East Asia, it is grown at higher elevations, e.g. in Puncak and Brastagi (Indonesia) and Baguio (the Philippines).
New Zealand spinach is usually consumed boiled. As the leaves tend to taste slightly bitter, it is advisable to blanch them before cooking. The leaves are, however, also used raw as an ingredient of salads. They are suitable for deep-freezing like ordinary spinach (Spinacia oleracea L.).
Production and international trade
New Zealand spinach has never become an important commercial vegetable in temperate areas due to the labour-intensive harvest. It is grown mainly as a small-scale home garden crop, and production data are not available. In Indonesia it is mainly traded to the supermarkets of the big cities.
New Zealand spinach is known as a good source of minerals, in particular Ca and Fe, and of vitamins. Per 100 g edible portion, it contains: water 93 g, protein 1-2 g, fat 0.3 g, carbohydrates 3-5 g, Ca 58-180 mg, Fe 2.5-3.8 mg, β-carotene 4.3 mg, vitamin B1 0.08 mg, vitamin B2 0.20 mg, niacin 0.5 mg, vitamin C 25-50 mg. The energy value is 80 kJ/100 g. It has been reported that most Ca is present as oxalates, not available to the human body. Consumption as a raw vegetable has also been discouraged because of a high saponin content. The 1000-fruit weight is 65-100 g.
- Fleshy, strongly branched, xerophytic, annual herb, covered all over with minute, shining, white papillae.
- Stems erect when young, afterwards trailing-ascending, terete or slightly angular, up to 1 m tall.
- Leaves succulent, spirally arranged; leaf-blade ovate-rhomboid-triangular, 1.5-11 cm × 1-7.5 cm, entire, dark green above, pale green beneath, dull on both sides; petiole 0.5-2.5 cm.
- Flowers bisexual, axillary, solitary or 2-3 together; perianth-tube turbinate, 1.5-2 mm long during anthesis, under each segment with a short hornlet, enlarging after anthesis; segments (3-)4(-5), 2-3 mm long, unequal, green externally, yellowish-green inside; stamens 4-10, filaments yellow; ovary semi-inferior, 2-9-celled, styles as many as cells.
- Fruit a conical, obconical or globular drupe, 2-5-horned, 2.5-12.5 mm long, 4-10-seeded, indehiscent.
- Seed subreniform.
Sowing "seed" usually consists of dry, hard fruits, each containing several true seeds. The "seeds" are reported to germinate erratically, taking from 2 weeks to more than 3 months. New Zealand spinach is a vigorous spreading plant developing a short upright shoot, and several radiating branches from its base, which lie prostrate on the ground. The plant flowers and fruits readily, with little apparent negative effects on growth. New Zealand spinach is predominantly self-pollinated, but cross-pollination may occur. The indehiscent fruits fall on the ground on ripening, the crop reseeding itself. Planting material (seeds or fruits) is usually traded without cultivar names.
New Zealand spinach occurs naturally in coastal areas. As a xerophyte it is capable of enduring long periods of drought. In the tropics it is easier to grow than Spinacia oleracea because of its better heat tolerance. The succulent leaves do not transpire rapidly.
In South-East Asia, it is grown mainly at elevations of 1000-1700 m, but with good care it can also be grown in the lowlands. A fertile, sandy, well-drained soil gives the best results.
Propagation and planting
New Zealand spinach is grown from seed, which is easily obtained, even under tropical conditions. Seeds should preferably be soaked in water for an hour to soften the seed-coat. Seedlings are usually raised in nurseries and transplanted when they have 6-7 leaves into permanent beds at distances of 50-100 cm either way. Soaked fruits (containing several true seeds) can also be direct-"seeded". Propagation by stem cuttings is rarely practised.
To obtain rapid, tender growth, manure and complete fertilizer should be amply supplied. A nitrogen fertilizer is advantageous as a side dressing to stimulate regrowth after harvesting. 30 t/ha of harvested shoots contain approximately 60 kg N, 15 kg P2O5 and 105 kg K2O, and therefore the total fertilizer application per ha should be 100 kg N, 25 kg P2O5and 150 kg K2O. Because initial growth is slow, New Zealand spinach can best be grown in alternating rows with other, quick-maturing vegetables. Once fully developed, one plant easily covers 1 m2of ground surface.
Diseases and pests
New Zealand spinach is relatively little affected by diseases and pests. Rot of the prostrate stems may occur, but this is insignificant on sandy soils. Old plants may degenerate by virus. Leafhoppers and aphids are sometimes troublesome. The root system is attacked by root knot nematodes.
When the central stem has grown to a height of 15 cm and the branches to a length of 15-20 cm, tops of 5-7.5 cm length may be cut for the first harvest (2-3 months after sowing). As the plant spreads over the soil, harvesting of new shoots may continue at weekly intervals over a period of several months. When regularly cut back, it may persist in the tropics as a short-lived perennial.
Yield can be 1.5 kg/plant or 30 t/ha. When growth becomes unsatisfactory, the mat of old plants may be pulled out, and the young plants which are developing underneath from fallen fruits, may be used for a new crop.
Handling after harvest
The leaves do not store well. They should be consumed soon after harvest or stored at 0°C and 95% relative humidity.
Genetic resources and breeding
There are no germplasm collections. Genetic improvement of the crop has not been undertaken to any significant degree.
New Zealand spinach is an easy to grow, nutritious vegetable and deserves a corner in any tropical vegetable garden. Due to its spreading habit, a few plants are sufficient for a regular supply. It is drought resistant, salt tolerant, and immune to most insect pests.
In temperate regions it has not been able to compete with the ordinary spinach because of the amount of labour involved in harvesting compared to the once-over harvest in Spinacia oleracea.
- Backer, C.A., 1951. Aizoaceae. Tetragonia. In: van Steenis, C.G.G.J. et al. (Editors), 1950- . Flora Malesiana. Series 1. Vol. 4. Noordhoff-Kolff, Djakarta, Indonesia. p. 275.
- Buishand, T., 1977. Groentetuin voor iedereen [Vegetable garden for anyone]. Kosmos, Amsterdam, the Netherlands. p. 279.
- Fritz, D., Stolz, W., Venter, F., Weichmann, J. & Wonneberger, C., 1989. Gemüsebau [Vegetable growing]. 9th revised edition. Ulmer, Stuttgart, Germany. pp. 307-308.
- Tindall, H.D., 1983. Vegetables in the tropics. MacMillan, London, United Kingdom. pp. 388-391.
- J.S. Siemonsma