Botany
Evergreen or sometimes deciduous, monoecious or rarely dioecious, small to medium-sized trees up to 20(-30) m tall; bole crooked (X. granatum) to straight and cylindrical (X. moluccensis), branchless for up to 10 m, up to 90(-100) cm in diameter, usually with small buttresses and snail roots, those of X. moluccensis bearing many short pneumatophores; bark surface smooth, irregularly flaking, whitish to yellow-brown (X. granatum) or rough, longitudinally fissured, flaking into oblong pieces, dark brown (X. moluccensis), inner bark green, red or pink; crown narrow and compact to bushy. Leaves arranged spirally, paripinnate with (1-)2-4(-5) pairs of leaflets, exstipulate; leaflets entire. Flowers in an axillary thyrse, 4-merous; calyx lobed; petals free, pinkish-yellow; staminal tube urceolate to cupular bearing 8 anthers; disk cushion-shaped, red; ovary superior, 4(-5)-locular with 3-4(-6) ovules in each cell, style short with a discoid stigma. Fruit a large, tardily dehiscing, subglobose capsule. Seeds 5-20, irregularly tetrahedral or pyramidal, attached to a central columella, with a corky testa. Seedling with hypogeal germination; cotyledons not emergent; hypocotyl not elongated; epicotyl bearing scales followed by simple leaves.
Growth is according to Rauh's architectural model, characterized by a monopodial trunk which grows rhythmically and so develops tiers of branches. Each new flush is marked by a few scales followed by pinnate leaves. In India early growth is rapid, over 60 cm in height in 2 months, and an annual diameter increment of 0.8 cm has been recorded. In Thailand a mean annual diameter increment of 1.3 cm was recorded for trees of approximately 10 cm in diameter. On the other hand, in Bangladesh the annual diameter increment of X. moluccensis was very small being 0.2 cm over a 13-year period. Growth characteristics vary greatly between different provenances. Flowering is usually in March-April; fruiting in June-July. Flowers are pollinated by bees. Usually only one fruit is present per inflorescence. The seeds float just below the water surface and are dispersed by ocean currents.
In the past there was much confusion about which name should be applied to which species. There has been complete confusion in the literature making it sometimes impossible to attribute certain data to a given species. The two most common species (X. granatum and X. moluccensis) are easily recognized by their bark features but are difficult to distinguish in the herbarium. X. rumphii can be recognized by its ovate to cordate leaflets.
Literature
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