MANGOSTEEN is indigenous to this part of the world and wild trees have been found in the jungle on the east coast of Malay Peninsula. It is believed to have been in cultivation throughout the Asian tropics for centuries, but there are no distinct varieties The fruit is well-known as one of the most delicious of all the tropical fruits and is termed the 'queen of fruits' and 'the finest fruit in the world'.
It is an evergreen tree of medium height, with a dense pyramidal crown. The tree grows to about 10-20 meters high at maturity. The sap is yellow. All plant parts excrete a yellow latex when damaged. The trunk is straight with low arched branches, and the slightly flaky bark is dark brown to blackish. There may be short, thick knobs on the trunk, which are the remains of earlier branches. New twigs are angled and green, becoming brown with age.
The leaves are borne on the end of new twigs. They are of varying sizes, about 20-25 cm by 9-12 cm. They are simple and in opposite pairs, unifoliate, thick and leathery. The colour varies from olive green to dark green above, and is slightly glossy, but is dull and almost yellow below. New leaves are pink. The midrib is pale and prominently raised on both surfaces. The leaf-stalks are thick and short, about 1.5cm long, fleshy-looking when new but becoming brown and wrinkled with age.
The yellowish-green flowers are unisexual dioecious. They are large, about 4-6 cm across, and are borne solitary or in pairs near the twig ends amongst the leaves. They are rather fleshy-looking with 4 large curved sepals and 4 petals, being flushed with pink or red. The globose ovary has a yellow, thick stigma which is divided into 4-8 lobes. The flowers open in the late afternoon. The petals of the female flowers quickly fall off while the sepals remain and are still visible as the fruits ripen.
Mangosteen is dioecious. However, only trees with female flowers are known in cultivation. Male trees are rare to non-existent. Almost all the flowers are purely female, and these develop into purplish fruits. The fruit is formed in a peculiar way without fertilisation; what is known as 'parthenogenesis' in the botanical sense. This peculiarity accounts for the lack of variation in the species.
The fruit is a berry and varies from 6 cm up to 9 cm in diameter. It is round but slightly flattened at each end. The smooth and firm rind is pale green at first and gradually turns purple or crimson-purple on ripening. The four large, rounded sepals remain on the fruit at the stalk end, and the apex is crowned with 5-8 flat woody lobes which always correspond to the number of fleshy segments inside. The fruit-stalk is thick, and varies from 1-2cm long. The rind, about 1cm thick, is deep crimson and fibrous. It contains a purple resin which will stain hands and clothes. Inside are 5-8 fleshy, ivory white segments which are the edible arils. They are extremely pleasant to taste but slightly sour. One to three of these segments may contain a large, light brown seed which adheres to the flesh. Seeds are formed from nucellar tissue in these parthenocarpic fruits.
The tree is slow growing, but is long-lived. From the seed, it takes about 15 years to fruit. It produces 500-1000 fruits annually. Fruits are produced twice a year. The seasons are roughly at the middle and towards the end of the year. Generally, their seasons coincide with those of the durian and rambutan. The yield is uncertain and is easily upset by unusual weather.
Mature fruits drop and bruise easily. For marketing, it is best to hand-harvest at early maturity before fruits are fully ripe. If harvested too soon, fruits do not develop full flavour. Fresh fruits can be marketed up to 5 days after harvest.
Mangosteen is excellent as a fresh fruit. It is considered as the choicest fruit of the tropics. The rind is rich in tannin and is dried for use as medicine by the local Chinese and Malays.
Mangosteen has always been a difficult tree to grow. Initial propagation is not easy even with seeds, as the viability of the seed is poor and short-lived. Propagation is by seed or grafting onto seedlings of the same species. Asexual propagation by approach grafting and wedge grafting have proved successful in mangosteen. The young tree requires shading when planted out in the open, as the leaves are easily scorched by hot sun, and eventually the plant will be stunted and killed.
The Mangosteen tree prefers a moist, hot climate with a short dry season. It thrives in deep, fertile, well-drained soil which is slightly acidic.
DATE: September 1989
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