Common Name: Karaya

General Information

Sterculia urens is a deciduous tree growing from 9 - 15 metres tall[]. The tree usually has a clean, crooked, short bole that can be up to 2 metres in diameter[].
Sterculia urens is the main source of 'Karaya Gum', used commercially in foods, as a medicine and for industrial purposes. The gum is harvested from the wild in large quantities[], and the tree is also harvested for local use as a food, medicine and source of materials. The tree is sometimes cultivated in India and Sri Lanka for medicinal and edible use of the gum; and is also grown as an ornamental[].

Known Hazards

The fruits are armed with stiff, stinging hairs that cause intolerable itching, if touched or handled; oil
removes the hairs, and the itching, effectively[].

Botanical References

Range

E. Asia - India, Sri Lanka, Bangladesh, Myanmar, Thailand, Cambodia, Laos, Vietnam.

Habitat

Dry rocky hills in Central and northern India, at elevations between 300 - 750 metres[]. Dry, tropical deciduous forests, often associated with Boswellia serrata, on hilltops, exposed ridges, rocky crevices, eroded slopes and similar habitats[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	12.00 m
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Sterculia urens is a plant of low elevations in the arid to moist tropics, where it is usually found at elevations from 300 - 750 metres[]. It grows best in areas where annual daytime temperatures are within the range 30 - 42°c, though it can tolerate 7 - 47°c[]. It can be killed by temperatures of -2°c[]. It prefers a mean annual rainfall within the range 750 - 1,200mm, but tolerates 200 - 2,000mm, usually growing in areas with a distinct dry season[].
Requires a sunny position, though seedlings are shade tolerant[, ]. Grows best in a light, well-drained soil[]. Very tolerant of poor, rocky soils[, ]. Established plants are very drought tolerant[]. Prefers a pH in the range 6 - 7, but tolerates 5.5 - 7.8[].
The trees can be tapped for their gum about 5 times during their lifetime[]. The gum is collected in India after making incisions or wounds in the trunk and branches of the tree. The gum that exudes from these wounds is allowed to solidify to form irregular tears that are consequently cleaned and sorted[].
The trees are generally worked under some form of coppice system on a rotation of 30 - 40 years[].

Edible Uses

The gum obtained from the trunk is used for making sweetmeats and is also eaten in curries[, ]. It is commonly used on a commercial basis, mainly as a stabilizer, emulsifier and thickener in a range of processed foods including French dressing, sherbets and ice-cream sticks[, ]. Known as gum karaya, it has been approved by Food and Agriculture Organization to be used as a safe food additive with the number E-416[].

Seeds - roasted[, , , ]. They yield an oil containing much stearin[]. Eaten on a local basis, though they are most commonly used as a famine food[].
The seeds are sometimes roasted and used as a substitute for coffee[, ].

Tender young roots - cooked. Eaten in times of famine[].

Medicinal

The gum is used as a bulk laxative[]. It is not absorbed by the body, but swells up inside the gut to provide a bulk of material that gently stimulates peristalsis[]. The gum is also used as a substitute for gum tragacanth to treat throat inffections[, ].
The gum is used in the pharmaceutical industry as a carrier for sparingly soluble drugs, allowing them to pass through the stomach unabsorbed and to then be absorbed in the colon by the actions of Enterobacteria[].

The root bark and the stem bark are used to improve fertility and to relieve rheumatoid arthritis[].

The bark, gum and leaves are used in the treatment of throat problems, contraction of uterus, cooling effect, foot cracks, general tonic, vomiting, delivery pain, bone fracture[].

The gum and mucilage contain aldobiuronic and aldotriouronic acids[].
The roots contains a coumarin, scopoletin[].
The gum of Sterculia villosa Roxb. (Udall Wood) resembles with that of S. urens[].
Diometin and chrysoeriol and their -O-glucosides were isolated from the wood[].

Agroforestry Uses:

A useful plant for reclaiming and reforesting bare, rocky land[, ].

Other Uses

A gum, known as 'Karaya Gum', is obtained from wounds made in the trunk[, ]. It exudes more quickly in the cool season[]. The gum is completely soluble in cold water, forming an almost colourless solution[]. It has many purposes, being used medicinally; as a pulp binder; as a thickening agent for printing dyes, as a size for textiles; in cosmetics; as a stabilizer, thickening agent and emulsifier in foods; as a denture adhesive, where the finely powdered gum is dusted on the dental plate and swells when it touches the moist surface of the gums, thus giving a comfortable and tight fit of the plate.[, , ].
The main constituent of the resin is a phlobatannin, containing 3 phenolic OH groups[].

The fibres obtained from the bark are used for making cordage[]. The bark can be stripped off the tree easily and yields a useful fibre suitable for making coarse cloth and ropes[].

The sap wood is a pale greyish-white; clearly demarcated from the red heartwood. The wood is heavy to very heavy, very strong and very hard, but poor in splitting and retention of shape[]. It planes and turns to a smooth finish and may also be suitable after seasoning and the adoption of suitable joining techniques for door and window frames, furniture and joinery. It is considered suitable for use as posts, beams, rafters and tool handles[].
The wood is used for fuel[].

Propagation

Seed - germination takes 10 - 15 days and gives nearly 100 % seedlings that reach 15 - 20cm in height n three months[].
A physical dormancy caused by the hard seed coat of the mature seeds of many species in this genus can be overcome by scarifying the seed. This is carried out by cutting away or abrading some of the seed coat to allow the ingress of water, though great care must be taken not to damage the embryo[]. The aril surrounding the seed should also be removed - this is easiest when it has been softened through soaking in water[]. The seeds germinate optimally at temperatures between 20 - 30°c. They can be sown in a nursery seedbed or in containers. A germination rate of about 95%, occurring within about 2 weeks can be expected if the seed has been properly treated[].

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