Butterfly Pea is a perennial and leguminous flowering vine widely distributed across the tropics and subtropics, which has made it difficult for botanists to trace its origins, though tropical Asia is suggested as the most likely region.
It is fast-growing and produces a large taproot below ground, above which grow finely hairy, slender, green herbaceous stems 3 to 5 m (10 to 15 ft) long. These twist and climbing their way up on any structure or nearby object, entwining and sometimes completely covering them.
The leaves are feathery, made up of small green oval leaflets 2 to 5 cm (0.8 to 2 in) long, arranged in two, three or four pairs along the length and with an extra leaflet at the tip.
The flowers are pea-like in shape, resembling flowers of other legumes, purple-blue in colour and stained white at the centre or less commonly pure white. They are borne singly or in pairs spaced far apart along the vine and bloom on and off throughout the year. Slender seedpods follow, 6 to 11 cm (2.3 to 4.3 in) long, green when young, becoming brown and dry with up to ten blackish seed inside.
Butterfly Pea can be trained to climb and cascade over walls, fences, arbours and trellises to quickly screen or shade an area, its feathery foliage and showy pea-like flowers an added bonus. It is also used for erosion control and in agriculture as green manure or orchard ground-cover, on account of its deep taproot, quick growth and nitrogen-fixing abilities.
The young seedpods and flowers are edible, the seedpods usually cooked as a vegetable and the flowers used as a decorative garnish or to add colour and interest to salads.
The herbaceous parts are highly palatable to livestock and it can be grown in pastures as forage, fresh-cut feed or harvested together with tall grasses for rotational hay or silage production. The fresh-cut parts, including the leaves, flowers and soft stems have a crude protein content of about 19% of their dry weight.
The blue flowers yield a dye containing ternatin, a pigment similar to litmus, which is widely used as an indicator of acidity and alkalinity. Aqueous extracts of the flower are traditionally used as a food colouring, to colour hair and to dye fabric and fibre. The dye can be made by drying the flowers, crushing them to a powder and then mixing the powder with ten parts water. Altering the pH of the dye liquor gives colours in the red and blue spectrum and adding mordants such as ferrous sulphate, copper sulphate or lemon juice help make the dye colour-fast.
The flowers are rich in Bioflavinoid, a natural compound found in modern-day hair products which reportedly stimulates hair growth and causes the hair to grow thick and lustrous.
The first part of the botanical name, 'clitoria', comes from the flower's resemblance to the female genitalia.
Grows naturally in sub-humid to moderately humid subtropical and tropical climates, generally in frost-free areas with annual lows of 15 to 25 °C, annual highs of 26 to 35 °C annual rainfall of 700 to 4500 mm and a dry season of 6 months or less. Under dry season conditions, the plant enters a dormancy stage where growth slows and the foliage dies down but recovers again when the rains return.
New plants are usually started from seed but can also be raised from cuttings. 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 to 8.5 and on sites with full to partial sun exposure. It has good tolerance to drought and limestone soils.
Butterfly Pea re-seed naturally. It is a declared noxious weed and invasive species in Australia and is assessed as a high weed risk species for Hawaii by the Hawaii Pacific Weed Risk Assessment project (HPWRA).
The mature seed are a strong purgative and should not be ingested.
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