Aglaia

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Aglaia

Description

Usually small to large trees, rarely bushes, with indumentum of stellate hairs or pel- tate scales; dioecious; trunk often with buttresses, bosses often present where branches have fallen off and these frequently bearing leafy shoots; crown sympodial; branched throughout or in the upper part only, or unbranched with a crown of leaves, branches usually ascending or patent or sometimes arching. Bark smooth or somewhat rough, sometimes (especially in the larger species) deciduous in squarish scales, usually with Longitudinal rows of lenticels. Leaves borne in spirals, widely sepa- rated on the apical shoots or close together with the petiole bases overlapping, usually inparipinnate with lateral and terminal leaflets usually similar, the basal pair of leaflets rarely markedly smaller in size, leaves rarely simple. Inflorescences usually axillary or supra-axillary, occasionally ramiflorous or cauliflorous, often several on an apical shoot. Flowers up to 10,000, terminal on branchlets, solitary or in sessile clusters, sometimes with bracteoles similar to the bracts, usually smelling of citronella, minute, 1–6(–10) mm long, subglobose, ellipsoid or obovoid. Flowers unisexual with well developed rudiments of the op- posite sex. Staminal tube 0.5–8 mm long, more or less truncate at the base, usually subglobose, obovoid, cup-shaped, the apex incurved or rarely shortly cylindrical, without appendages, sometimes with stellate or simple hairs on the inner surface, aperture small to large with an entire, crenate or shallowly lobed margin; anthers (3–)5–10(–21), usually in a single whorl, rarely two or more overlapping whorls, occasionally with stellate or simple hairs, broadly or narrowly ovoid, dehiscing by two longitudinal slits, inserted on the inner surface of the tube either just below and protruding through the aperture and pointing towards the centre of the flower or more or less vertical against the inner surface of the tube, curved to follow the shape of the tube and partially or completely included, rarely inserted on the margin of the tube; anthers in the female flowers similar but sterile, usually not dehiscing and without pollen, rarely with a few misshapen pollen grains. Ovary l–3(–10)-locular, superior, depressed-globose or ovoid with dense stellate hairs or peltate scales; locules with 1 or 2 collateral or super- posed ovules, where carpels more than 1, placentation axial. Fruits subglobose, obovoid or ellipsoid, indehiscent or a loculicidal capsule with 1–3 or rarely 4 or 10 locules each with one seed or rarely 2. Seeds large, usually with an aril or sarcotesta nearly or completely covering the seed.

Distribution

Asia-Tropical: New Guinea present, Australasia: Northern Territory (Northern Territory present); Queensland (Queensland present); Western Australia (Western Australia present), From Sri Lanka and India through Myanmar (Burma), S China, and Taiwan present, Indonesia present, Malaysia present, New Caledonia present, New Hebrides present, Pacific: Fiji (Fiji present), Solomon Islands present, east to the island of Samoa in Polynesia and north to the Marianne Islands (Saipan, Roti and Guam) and the Caroline Islands (Palau and Ponape) in Micronesia present, the Philippines present
In total 105 species, of which 84 species in Malesia. From Sri Lanka and India through Myanmar (Burma), S China, and Taiwan, Indochina, Malaysia, Indonesia, the Philippines, New Guinea, Solomon Islands, Vanuatu (New Hebrides), New Caledonia, Australia (Queensland, Northern Territory and Western Australia), Fiji, east to the island of Samoa in Polynesia and north to the Marianne Islands (Saipan, Roti and Guam) and the Caroline Islands (Palau and Ponape) in Micronesia

Ecology

Pollinators unknown; field investigations by the author suggest small dipterans and possibly stingless bees .

Dispersal is by vertebrates. See , where the investigation of 10 species is described. The seeds from dehiscent fruits (section Amoora) are dispersed mainly by birds and the arils are red- skinned, easily removed from the testa, rich in lipid (28–61% dry weight) and odourless. The aril in these species can be easily separated from the rest of the seed, and this probably means that it is easily removed by the action of the gizzard or gut of the dis- persing birds, which regurgitate or pass the seeds unharmed. In species with indehis- cent fruits the seeds are dispersed by primates and the arils are white, yellow, orange or brown, gelatinous and translucent, firmly attached to the testa, high in sugars (16–26% dry weight) and in sweet-tasting amino acids (such as alanine, γ-aminobutyric acid, gly- cine, and asparagine or aspartic acid), relatively low in lipid (3–11%) and have a char- acteristic odour. The aril adheres firmly to the testa and this, together with its gelatinous nature, probably encourages primates to swallow the seeds or carry them away from the fruiting tree before eating the flesh and discarding the seed.

Several features in the position and architecture of the infructescence, and in the posi- tion, size and structure of the fruit are also related to the mode of dispersal. The red- skinned arils of dehiscent fruits contrast with the white inner pericarp which is exposed on dehiscence and the pink or brick-red outer surface of the pericarp; dehiscence of the firuit makes it possible for the seed to be extracted easily by the bill of a bird. Dehiscent fruits are borne in small numbers on infructescences which have a short, stiff peduncle, so that they remain close to the subtending twig or branch of the tree, which provides a perch for birds feeding on the arillate seeds.

When the fruits are large, the infructescences are borne on stout shoots; the seeds are large, and only large birds such as hornbills are able to swallow them. In species with smaller fruits, the infructescences are borne on slender shoots; it is more difficult, al- though still possible, for large birds to reach the fruits, but seeds are more frequently taken by smaller birds. Field observations suggest that the large-seeded dehiscent spe- cies of Aglaia are dispersed by hornbills and possibly fruit pigeons, and that the smaller- seeded species are dispersed by hornbills and an array of smaller birds, including bul- buls, broadbills and barbets. The small birds probably effect mainly local dispersal, but hornbills and pigeons are known to fly distances of 100 km or more and could be impor- tant in longer distance dispersal. The seeds are accessible to primates as well as birds, but there are no confirmed observations of primates feeding on seeds from species of Aglaia which have dehiscent fruits.

In indehiscent fruits the pericarp is orange, pinkish-orange or brown and they are borne near the ends of slender branches or in large hanging infructescences, sometimes with a long peduncle, where they can be reached and manipulated by long-armed and dexterous primates. The primates break open and peel off the pericarp and remove the seed. At least two species of monkey, the Banded Leaf Monkey and the Long-tailed or Crab Macaque and three species of ape, the Orang Utan (Pongo pygmaeus abelii Lesson), the Siamang and the White-handed Gibbon , are known to ingest the seeds of Aglaia. In these indehiscent species, the seeds are inaccessible to most birds either because of the position of the infructescence or because the bird cannot manipulate the fruit to remove the pericarp and gain access to the seed.

Other animals in addition to primates might occasionally be dispersers in Sundaland, although they appear to be relatively unimportant. Squirrels are mainly destructive but occasionally disperse seeds over short distances. Terrestrial rodents and ground feeding birds such as the Crested Wood Partridge may play a similar role. Seeds of Aglaia elaeagnoidea have been found in the faeces of Paradoxurus her- maphroditicus (Pallas) (Viverridae, the civet family). Elephants, rhinoceros, tapirs and some deer are known to feed on fallen fruits of other plant families and may also con- tribute to the dispersal of Aglaia seeds. Bat-dispersal is a possibility for some species.

The total geographical range of Aglaia, however, extends far beyond the eastern lim- its of the distribution of primates and of some of the bird families that are thought to be the main dispersal agents of Aglaia to the west of Wallace’s Line. Species with dehis- cent and indehiscent fruits occur east of Wallace’s Line but the fruit structure, dehis- cence and the aril type are known for only a few of these species.

Fruit pigeons, which occur throughout the range of Aglaia and some Australasian bird families such as the Birds of Paradise (Paradisaeidae), Bower Birds (Ptilonorhyn- chidae) and the flightless Cassowaries (Casuariidae) are likely to be dispersers in Aus- tralasia . Pigeons may have transported the seeds of Aglaia species with capsular fruits across Wallace’s Line. They might therefore have played an important part in bringing about the collective geographical range of Aglaia, which lies entirely within the area of distribution of Ducula and Ptilinopus, the principal genera of fruit-eating pigeons in the Far East. Primates, which are important dispersers of the indehiscent species of Aglaia in Sundaland, are absent from Australasia and their role in dispersal may be filled there by terrestrial or arboreal fruit-eating marsupials, rodents, bats or ground-dwelling birds.

Cytology

The chromosomes are minute and the numbers are high; 2n = 64, 84 in the Malesian species examined by Pannell .

Uses

The wood of Aglaia is sometimes used locally for building or making furni- ture and the fleshy layer around the seeds of some species is edible, although inferior in quality to that of Lansium domesticum Correa agg., the Langsat. Trees of one species, Aglaia korthalsii, are grown for their fruits in villages in the state of Kelantan, Penin- sular Malaysia. The flowers of A. odorata Lour, are used by the Chinese for scenting tea and in Java for scenting clothes (see under Cultivated species, below and p. 383). More recently investigation of the essential oil of the root bark of a species (incorrectly referred to as A. odoratissima) from Karnataka in India has revealed that the oil pos- sesses antimicrobial and anthelmintic activities in vitro and that it has a depressant action on the central nervous system of mice . See also the paragraph on Phytochemistry, p. 8.

Notes

Two features of the genus make it particularly well suited for ecological study. First, Aglaia trees are rarely grown by man, so it can be assumed that trees growing in the forest are of wild origin. Second, there are usually several, and often as many as 12, species of Aglaia in a single forest site, which makes it possible to compare the reproductive biology of co-existing species and this contributes to an understanding of the plant and animal community of the forest as a whole. Studies of the reproductive biology of this large and common rain forest genus have therefore added to our general understanding of the role of animals as pollinators and dispersers of rain forest trees and of the relevance of this both to conservation and to the regeneration of tropical forest after logging. See . The study of the interdependence between plants and animals is one of the most important elements in understand- ing the forest ecosystem, crucial to both conservation and the sustainable management of forests, but it is an approach which has often been neglected. Further study of the complex species in this genus (A. lawii, A. elaeagnoidea, A. korthalsii, A. leptantha, A. edulis, A. elliptica, and A. tomentosa) is likely to prove to be particularly valuable, because they are often widespread and have apparently adapted to different physical and biotic conditions.

Citation

Pannell 1992 – In: Kew Bull., Add. Ser. p 34
Harms 1940 – In: Engl. & Prantl, Nat. Pflanzenfam., ed. 2, 19bl. p 140
Harms 1940 – In: Engl. & Prantl, Nat. Pflanzenfam., ed. 2, 19bl. 128.