Psophocarpus tetragonolobus

Common name: Winged bean

Other common names: Asparagus bean, Dragon bean, Four-angled bean, Goa bean, Manila bean

Names in non-English languages: India Thailand Portuguese China

Description

Winged Bean is a strong-growing perennial vine originating in India and Southeast Asia and is cultivated there for its seedpods, which are cooked and eaten as a vegetable.

Mature vines are made up of rigid, herbaceous stems up to 5 m (16 ft) long and 1 cm (0.4 in) in diameter, off of which branch soft twining and climbing stems.

Leaves trifoliate, each made up of three dark green, broadly oval and pointed leaflets. These attach to the stems by way of long leaf-stalks and remain on the vine in all seasons.

Flowers large and pea-like, either pale blue or, less commonly, white and borne in clusters of up to ten arising at nodes along the stems. These are followed by four-angled green and winged seedpods, the wings with wavy margins, sometimes with purple markings. When mature they are 15 to 20 cm (6 to 8 in) long with small white, yellow, brown or black oval seed inside, depending on the variety.

Use

The young seedpods are a good substitute for green beans and are commonly eaten steamed or in stir-fries. Similar to green beans, they become fibrous with age, so are best harvested when about half their mature size, from about 8 to 10 cm (3 to 4 in) in length.

In cool subtropical and tropical highland climates, the vine enters a dormant stage and the roots develop tubers or storage roots that can be cooked and eaten as a starchy vegetable, or peeled and eaten raw in salads. These do not usually develop in tropical lowland climates with continually warm and wet conditions.

The seed oil is nutritionally valuable, with qualities similar to that of soybean oil. However, the plant's vining habit makes mechanically harvesting the seed impractical and economically unviable.

The flowers are edible and make a colourful and interesting addition to any salad. In Japan, they are dipped in tempura batter and deep fried.

Winged Bean is not generally used as green manure but is sometimes grown as a nitrogen-fixing green mulch (cover-crop) in banana plantations to protect against soil erosion, as well as to enrich the soil, conserve moisture and control weeds.

Climate

Grows naturally in humid subtropical and tropical climates, generally frost-free areas with annual lows of 13 to 25 °C, annual highs of 24 to 35 °C, annual rainfall of 900 to 4000 mm and a dry season of 6 months or less.

Winged bean vines do poorly in high elevation climates, or where the average low of the warmest month falls below 18 °C (64 °F), the cool conditions causing low germination rates, slow growth and delayed or poor flowering.

Although the vine will die-back in lowland areas with a distinct cold or dry season, it will re-sprout from the roots when warmth and moisture returns.

Winged Bean vines are most productive in areas closest to the equator, where short days induce almost contentious flowering. However, the plant has been successfully introduced in subtropical areas and has flourished in South Florida (25° to 27°N), Brisbane (27° S) and Perth (32° S).

Growing

New plants are usually started from seed sown directly in the soil, or are sown first in containers with a free-draining potting-mix then transplanted as seedlings to the planting site. The seed benefit from pre-treatment before sowing to encourage germination. This can be done by soaking them in just boiled water that is then left to cool.

The plants performs best on free-draining clay-loam, loam and sandy-loam soils of a moderately acid to alkaline nature, generally with a pH of 5.0 to 8.0, and on sites with full sun exposure.

Planting is done mostly on prepared beds enriched with organic matter and the vines provided with stakes or stout trellises to climb up on, which is essential for good vine growth and pod production. Plants begin to flower in three to four months.

Around 15,000 kgs of green pods are harvested, on average, per hectare (13,000 pounds per acre) in commercial operations, but as much as 35,000 kgs per hectare (31,000 pounds per acre) has been reported in experimental plantings.

Problem features

Winged Bean is listed as a weed in at least one reference publication but there does not appear to be any record of it anywhere as a serious weed, despite it being widely introduced and cultivated.

Where it will grow

With irrigation or groundwater

References

Books

  • Adams, C. D. 1972, Flowering plants of Jamaica, University of the West Indies, Mona, Greater Kingston

  • Allen, O. N. & Allen, E. K. 1981, The Leguminosae : a source book of characteristics, uses, and nodulation, University of Wisconsin Press, Madison, Wisconsin

  • Herklots, G. A. C. 1972, Vegetables in south-east Asia, Allen and Unwin, London

  • Litzenberger, S. C. 1974, Guide for field crops in the tropics and the subtropics, Office of Agriculture, Technical Assistance Bureau, Agency for International Development (USAID), Washington D.C.

  • Macmillan, H. F. 1943, Tropical planting and gardening : with special reference to Ceylon, 5th ed, Macmillan Publishing, London

  • National Research Council (Board on Science and Technology for International Development) 1975, Underexploited tropical plants with promising economic value, National Academic Press, Washington D. C.

  • Norrington, L. & Campbell, C. 2001, Tropical food gardens : a guide to growing fruit, herbs and vegetables in tropical and sub-tropical climates, Bloomings Books, Hawthorn, Victoria

  • Randall, R. P. 2002, A global compendium of weeds, R.G. and F.J. Richardson Press, Melbourne

  • Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

  • Rubatzky, V. E. & Yamaguchi, M. 1997, World vegetables : principles, production, and nutritive values, 2nd ed., Chapman & Hall, New York

  • Tindall, H. D 1983, Vegetables in the Tropics, Macmillan Press, London

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