The tamarind, a slow-growing, long-lived, massive tree reaches, under favorable conditions, a height of 80 or even 100 ft (24-30 m), and may attain a spread of 40 ft (12 m) and a trunk circumference of 25 ft (7.5 m). It is highly wind-resistant, with strong, supple branches, gracefully drooping at the ends, and has dark-gray, rough, fissured bark. The mass of bright-green, fine, feathery foliage is composed of pinnate leaves, 3 to 6 in (7.5-15 cm) in length, each having 10 to 20 pairs of oblong leaflets 1/2 to 1 in (1.25-2.5 cm) long and 1/5 to 1/4 in (5-6 mm) wide, which fold at night. The leaves are normally evergreen but may be shed briefly in very dry areas during the hot season. Inconspicuous, inch-wide flowers, borne in small racemes, are 5-petalled (2 reduced to bristles), yellow with orange or red streaks. The flowerbuds are distinctly pink due to the outer color of the 4 sepals which are shed when the flower opens.
The fruits, flattish, beanlike, irregularly curved and bulged pods, are borne in great abundance along the new branches and usually vary from 2 to 7 in long and from 3/4 to 1 1/4 in (2-3.2 cm) in diameter. Exceptionally large tamarinds have been found on individual trees. The pods may be cinnamon-brown or grayish-brown externally and, at first, are tender-skinned with green, highly acid flesh and soft, whitish, under-developed seeds. As they mature, the pods fill out somewhat and the juicy, acidulous pulp turns brown or reddish-brown. Thereafter, the skin becomes a brittle, easily-cracked shell and the pulp dehydrates naturally to a sticky paste enclosed by a few coarse strands of fiber extending lengthwise from the stalk. The 1 to 12 fully formed seeds are hard, glossy-brown, squarish in form, 1/8 to 1/2 in (1.1-1.25 cm) in diameter, and each is enclosed in a parchmentlike membrane.
Native to tropical Africa, the tree grows wild throughout the Sudan and was so long ago introduced into and adopted in India that it has often been reported as indigenous there also, and it was apparently from this Asiatic country that it reached the Persians and the Arabs who called it "tamar hindi" (Indian date, from the date-like appearance of the dried pulp), giving rise to both its common and generic names. Unfortunately, the specific name, "indica", also perpetuates the illusion of Indian origin. The fruit was well known to the ancient Egyptians and to the Greeks in the 4th Century B.C.
The tree has long been naturalized in the East Indies and the islands of the Pacific. One of the first tamarind trees in Hawaii was planted in 1797. The tamarind was certainly introduced into tropical America, Bermuda, the Bahamas, and the West Indies much earlier. In all tropical and near-tropical areas, including South Florida, it is grown as a shade and fruit tree, along roadsides and in dooryards and parks. Mexico has over 10,000 acres (4,440 ha) of tamarinds, mostly in the states of Chiapas, Colima, Guerrero, Jalisco, Oaxaca and Veracruz. In the lower Motagua Valley of Guatemala, there are so many large tamarind trees in one area that it is called "El Tamarindal". There are commercial plantings in Belize and other Central American countries and in northern Brazil. In India there are extensive tamarind orchards producing 275,500 tons (250,000 MT) annually. The pulp is marketed in northern Malaya and to some extent wherever the tree is found even if there are no plantations.
In some regions the type with reddish flesh is distinguished from the ordinary brown-fleshed type and regarded as superior in quality. There are types of tamarinds that are sweeter than most. One in Thailand is known as 'Makham waan'. One distributed by the United States Department of Agriculture's Subtropical Horticulture Research Unit, Miami, is known as 'Manila Sweet'.
Very young trees should be protected from cold but older trees are surprisingly hardy. Wilson Popenoe wrote that a large tree was killed on the west coast of Florida (about 7.5º lat. N) by a freeze in 1884. However, no cold damage was noted in South Florida following the low temperatures of the winter of 1957-1958 which had severe effects on many mango, avocado, lychee and lime trees. Dr. Henry Nehrling reported that a tamarind tree in his garden at Gotha, Florida, though damaged by freezes, always sprouted out again from the roots. In northwestern India, the tree grows well but the fruits do not ripen. Dry weather is important during the period of fruit development. In South Malaya, where there are frequent rains at this time, the tamarind does not bear.
The tree tolerates a great diversity of soil types, from deep alluvial soil to rocky land and porous, oolitic limestone. It withstands salt spray and can be planted fairly close to the seashore.
Tamarind seeds remain viable for months, will germinate in a week after planting. In the past, propagation has been customarily by seed sown in position, with thorny branches protecting the young seedlings. However, today, young trees are usually grown in nurseries. And there is intensified interest in vegetative propagation of selected varieties because of the commercial potential of tamarind products. The tree can be grown easily from cuttings, or by shield-budding, side-veneer grafting, or air-layering.
Nursery-grown trees are usually transplanted during the early rainy season. If kept until the second rainy season, the plants must be cut back and the taproot trimmed. Spacing may be 33 to 65 ft (10-20 m) between trees each way, depending on the fertility of the soil. With sufficient water and regular weeding, the seedlings will reach 2 ft (60 cm) the first year and 4 ft (120 cm) by the second year.
In Madagascar, seedlings have begun to bear in the 4th year; in Mexico, usually in the 5th year; but in India, there may be a delay of 10 to 14 years before fruiting. The tree bears abundantly up to an age of 50-60 years or sometimes longer, then productivity declines, though it may live another 150 years.
Mexican studies reveal that the fruits begin to dehydrate 203 days after fruit-set, losing approximately 1/2 moisture up to the stage of full ripeness, about 245 days from fruit-set. In Florida, Central America, and the West Indies, the flowers appear in summer, the green fruits are found in December and January and ripening takes place from April through June. In Hawaii the fruits ripen in late summer and fall.
Tamarinds may be left on the tree for as long as 6 months after maturity so that the moisture content will be reduced to 20% or lower. Fruits for immediate processing are often harvested by pulling the pod away from the stalk which is left with the long, longitudinal fibers attached. In India, harvesters may merely shake the branches to cause mature fruits to fall and they leave the remainder to fall naturally when ripe. Pickers are not allowed to knock the fruits off with poles as this would damage developing leaves and flowers. To keep the fruit intact for marketing fresh, the stalks must be clipped from the branches so as not to damage the shell,
A mature tree may annually produce 330 to 500 lbs (150-225 kg) of fruits, of which the pulp may constitute 30 to 55%, the shells and fiber, 11 to 30 %, and the seeds, 33 to 40%.
To preserve tamarinds for future use, they may be merely shelled, layered with sugar in boxes or pressed into tight balls and covered with cloth and kept in a cool, dry place. For shipment to processors, tamarinds may be shelled, layered with sugar in barrels and covered with boiling sirup. East Indians shell the fruits and sprinkle them lightly with salt as a preservative. In Java, the salted pulp is rolled into balls, steamed and sun-dried, then exposed to dew for a week before being packed in stone jars. In India, the pulp, with or without seeds and fibers may be mixed with salt (10%), pounded into blocks, wrapped in palmleaf matting, and packed in burlap sacks for marketing. To store for long periods, the blocks of pulp may be first steamed or sun-dried for several days.
One of the major pests of the tamarind tree in India is the Oriental yellow scale, Aonidiella orientalis. Tamarind scale, A. tamarindi, and black, or olive, scale, Saissetia oleae, are also partial to tamarind but of less importance. Butani (1970) lists 8 other scale species that may be found on the tree, the young and adults sucking the sap of buds and flowers and accordingly reducing the crop.
The mealybug, Planococcus lilacinus, is a leading pest of tamarind in India, causing leaf-fall and sometimes shedding of young fruits. Another mealybug, Nipaecoccus viridis, is less of a menace except in South India where it is common on many fruit trees and ornamental plants. Chionaspis acuminata-atricolor and Aspidiotus spp., suck the sap of twigs and branches and the latter also feeds on young fruits. White grubs of Holotrichia insularis may feed on the roots of young seedlings. The nematodes, Xiphinema citri and Longidorus elongatus may affect the roots of older trees. Other predators attacking the leaves or flowers include the caterpillars, Thosea aperiens, Thalarsodes quadraria, Stauropus alternus, and Laspeyresia palamedes; the black citrus aphid, Toxoptera aurantii, the whitefly, Acaudaleyrodes rachispora; thrips, Ramaswamia hiella subnudula, Scirtothrips dorsalis, and Haplothrips ceylonicus; and cow bugs, Oxyrhachis tarandus, Otinotus onerotus, and Laptoentrus obliquis.
Fruit borers include larvae of the cigarette beetle, Lasioderma serricorne, also of Virachola isocrates, Dichocrocis punctiferalis, Tribolium castaneum, Phycita orthoclina, Cryptophlebia (Argyroploca) illepide, Oecadarchis sp., Holocera pulverea, Assara albicostalis, Araecerus suturalis, Aephitobius laevigiatus, and Aphomia gularis. The latter infests ripening pods on the tree and persists in the stored fruits, as do the tamarind beetle, Pachymerus (Coryoborus) gonogra, and tamarind seed borer, Calandra (Sitophilus) linearis. The rice weevil, Sitophilus oryzae, the rice moth, Corcyra cepholonica, and the fig moth, Ephestia cautella, infest the fruits in storage. The lesser grain borer, Rhyzopertha dominica bores into stored seeds.
In India, a bacterial leaf-spot may occur. Sooty mold is caused by Meliola tamarindi. Rots attacking the tree include saprot, Xylaria euglossa, brownish saprot, Polyporus calcuttensis, and white rot, Trametes floccosa. The separated pulp has good keeping quality but is subject to various molds in refrigerated storage.