Batuan trees are native to the south eastern region of Asia and, on average they grow up to a height of about 25 meters. Belonging to the family Clusiaceae, these trees are found copiously in forests that are located in low altitudes, mostly in Vietnam and the Philippines.
Since the fruit of batuan has an extremely sour taste, they are usually used in the form of a souring agent by the natives in their food recipes.
In fact, batuan trees are closely related to mangosteen. These trees are classified in the sub-globose fruits category. The seed pods of these trees contain multicoloured sections that enclose numerous sour flavoured seeds. Batuan trees produce oblong or ovate shaped leaves, which are roughly 15 cm in length.
They are rounded on either end, but medium sized. The leaves are glossy and smooth. The red flowers of batuan trees are small and appear in clusters on pendulous branches.
The fruits, whose external skin is firm, contain copious number of seeds and have an extremely acidic pulp. These fruits are small and rounded, measuring roughly 4 cm in diameter. The bark of these trees has a black color.
Although you can eat ripe batuan fruits raw, you should bear in mind that they are extremely acidic. Similar to any fruit of other Garcinia variety, for instance kokum (which is found on abundance of India's western coast) or Garcinia pedunculata, you can also preserve batuan after cutting the fruit into slender pieces and subsequently drying them in sunlight.
In India's Assam province, Bodos cook the unripe batuan fruit in the form of a vegetable along with fish. They also prepare chutney by boiling batuan fruit. People in Assam use the dried out and preserved batuan slices with black green pulses to prepare a very popular, but somewhat acidic curry.
The dried batuan fruits are an effective traditional herbal remedy for dysentery. In Ayurveda, the ancient Indian medicine system, batuan fruits are employed for treating a number of conditions, including dysentery and gastritis. In addition, it is claimed that batuan possesses anti-inflammatory properties.
When the bark of batuan trees is cut it gives out a yellowish resin known as gamboge, which has several uses. This resin is used in foods, medicine and paints. Moreover, this resin can also be used in the form of a rootstock for Garcinia mangostana (mangosteen).
It is said that consuming fresh batuan fruits helps to lower blood pressure and, hence, they are useful for people with hypertension. The resin or gamboge exuded from batuan is applied to the skin to heal irritated skin.
In Ayurvedic medicine, the yellow resin exuded by batuan plant is dried out and marketed under the label Gamboge or Kokum. When taken in doses of anything between 10 cgm and 15 cgm, gamboge works as a laxative. However, when this latex is used in higher doses such as 30 cgm to 50 cgm, it produces profuse evacuation accompanied by fierce colicky pains.
Moreover, when used in extremely high doses, gamboge works as a potent poison. Gamboge is often used in the form of a hydragogue cathartic to drain out fluid constituents from the blood, much in the same way as in asthma, dropsy, as well as cerebral and pulmonary congestion.
This resin is also employed as a vermifuge to expel various parasites and worms from the intestines. Gamboge is seldom used independently, but always administered with some other herbs, such as aloe vera, calomel, rhubarb, jalap and others.
In the Malabar, Canara, Sri Lanka (formerly known as Ceylon) and Singapore, people employ the following method to extract gamboge from batuan. At the onset of monsoon (the rainy season in the tropics and sub-tropical regions), people make a spiral incision in the bark encircling roughly half of the trees' trunk.
Then they insert a bamboo piece at the place where they want to collect the milky juice, which exudes slowly from the cut over many months. After some time, the juice turns viscid and subsequently becomes solid when it is exposed to the air.
On average, one batuan tree yields resin that is sufficient to fill at least three inter-nodal sections of the bamboo - each segment measures roughly 50 cm in length and anything between 3 cm and 5 cm across.
People where these trees grow naturally use batuan, a common food item, in several local recipes mainly for its acidic as well as sour flavour. In fact batuan is mostly found on the islands of Negros. It is also found in Panay, a nearby island. Having a shape similar to tomatoes, batuan is a green colored, hard fruit. In the rainforests in Negros, this fruit is found growing abundantly in the wild.
Unripe batuan is cooked along with fish and pork as a souring agent. It is also used in soups, for instance tinola and sinigang soups. On the other hand, the ripe fruit can be consumed raw from hand, but it has a very acidic flavour. People also preserve the fruits in the form of jams after drying.
They can also be pickled. In the Negros as well as in some places in Panay, you can find batuan fruits in the local markets. Nevertheless, the natural habitat of batuan trees, which bear these fruits, is declining very rapidly owing to deforestation by the locals.
Moreover, these days, people are not very inclined to cook this typical food at home because the cooking as well as eating habits of people in the Philippines have become very westernized. Gradually, they are moving away from their traditional recipes, which are rapidly losing popularity.
It is worth mentioning here that batuan was identified as one of the 300 species of fruit-bearing trees that either have immense commercial importance or having the potential to become economically important. According to sources, batuan is severely under-utilized despite the fact that it is a valuable fruit tree that can be grown in home gardens.
Similar to any fruit of the Garcinia varieties, one can also preserve batuan, the fruit borne by binucao trees, by slicing them into slender pieces and subsequently drying them in the sun. These fruits are also useful for making jams and pickles, in addition to eating them raw.
Considering the fact that batuan trees are logged for the purpose of shifting agriculture, the population of trees growing in the wild is reducing very rapidly. Having said this, it is very important to initiate measures to protect this plant species from becoming extinct. This can be achieved by planting more batuan trees. Batuan trees are dioecious and, hence, one cannot determine their sex just by seeing them during their planting.
According to sources, traditionally eating the fruits of binucao is considered to be a healthy practice. Moreover, it is rather difficult to propagate plant of this genus from their seeds as the seeds of most species belonging to this genus are very sluggish in developing roots, even when they are sown fresh. Usually, it takes six months or maybe be even longer for the seeds to germinate and take root.
A study involving the phytochemicals present in batuan leaf extract revealed that it contained 15 new cytotoxic chemicals, gaudichaudiic acid A-E, gaudichaudione A-H, and familiar compounds like forbesione and morellic. In addition, analysis of the bark helped to isolated novel gaudichaudiic acids F-I.