Neem is a fast growing tree that usually reaches a height of 15-20 m, and under very favorable conditions up to approximately 30-35 m. As a rule it is a evergreen tree, but under extreme circumstances, such as extended dry periods, it may shed most of nearly all of its leaves. The branches spread widely. The fairly dense crown is roundish or oval and may reach a diameter 15-20 m in old free standing specimens.
The trunk is relatively short, straight and may reach a girth of 1.5-3.5 m. The bark is hard fissured or scaly and whitish-gray to reddish-brown. The sap wood is grayish-white and the heart wood reddish.
The root system consists of a strong taproot and well developed lateral roots. The lateral surface root may reach over 18 m. Vesicular-arbuscular mycorrhiza (VAM) is associated with the rootlets categorized neem as a highly VAM dependant plant species.
The leaves are unpaired, pinnate, 20-30 cm long and the medium to dark green leaflets, which number up to 31, are approximately 3-8 cm long. The terminal leaf is often missing. The petioles are short. The shape of mature leaflets is more or less asymmetric.
Natural hybrids between A. indica and A. Siamensis , found in Thailand on places where both species grow together, have an intermediate position regarding the shape and consistency of the leaflets.
The white, gragrant flowers are arranged in axillary, normally more or less drooping panicles which are up to 25 cm long.
The glabrous fruits are olive- like drupes which vary in shape from elongate ovea to nearly roundish and when ripe are 1.4-2.8 x 1.0-1.5 cm . They are green when young and yellowish-green to yellow, rarely reddish when mature. The fruit skin (exocarp) is thin and the bitter-sweet pulp (mesocarp) is yellowish-white and very fibrous. The mesocarp is 0.3-0.5 cm thick. The white hard ‘shell (endocarp) of the seed encloses one, rarely two and very rarely three elongated seed kernels having brown testa.
The neem is native of Indian subcontinent, it is widely distributed by introduction, mainly in the drier (arid) tropical and subtropical zones of Asia, Africa, the Americas, Australia and the South Pacific islands. In India it is widely distributed in many states. In Myanmar it is very common in the central parts of the country.
In the South Pacific neem occurs in the Fiji Islands. In Australia it was first introduced about 60-70 years ago. In Indonesia, neem exists mainly in the low-lying northern and eastern parts of Java and in the frier islands to the east (Bali, Lombok, Sumbawa). In the Philippines it was introduced during the seventies and eighties of the last century. In China, A. indica was planted on subtropical island of Hainan and southern china. In Nepal neem trees are found in the southern, low-lying areas (Tarai region). In Sri Lanka it is widespread in the drier northern parts of the island.
In Iran, neem trees grow along the coast up t the Chat el Arab in Iraq on the Arabian peninsula. In Qatar and Abu Dhabi neem was planted under irrigation using desalted seawater along avenues and parks. A large plantation was established on the Arafat plains near Makkah to provide shade for pilgrims.