|Winged bean flowers and leaves|
|Psophocarpus tetragonolobus |
The winged bean plant grows as a vine with climbing stems and leaves, 3–4 m in height. It is an herbaceous perennial, but can be grown as an annual. It is generally taller and notably larger than the Common bean. The bean pod is typically 15–22 cm (6–9 in) long and has four wings with frilly edges running lengthwise. The skin is waxy and the flesh partially translucent in the young pods. When the pod is fully ripe, it turns an ash-brown color and splits open to release the seeds. The large flower is a pale blue. The beans themselves are similar to soybeans in both use and nutritional content (being 29.8% to 39% protein).
The plant is one of the best nitrogen fixers with nodulation accomplished by the soil bacterium Rhizobium. Because of its ability to fix nitrogen from the atmosphere, the plant requires very little or no fertilizers.
Being a tropical plant, it is sensitive to frost. Most plants will not flower if the day length is more than 12 hours, meaning they will not produce pods in most temperate zones, although day length neutral cultivars do exist. The seeds have a hard coat and it helps to soak them before planting to hasten germination. The plant grows very quickly, reaching a length of four meters in a few weeks.