Neem is a fast-growing tree that can reach a height of 15-20 m (about 50-65 feet), rarely to 35-40 m (115-131 ft.). It is evergreen but under severe drought it may shed most or nearly all of its leaves. The branches are wide spread. The fairly dense crown is roundish or oval and may reach the diameter of 15-20 m in old, free-standing specimens.
The trunk is relatively short, straight and may reach a diameter of 1.2 m. The bark is hard, fissured or scaly, and whitish-grey to reddish-brown. The sapwood is greyish-white and the heartwood reddish when first exposed to the air becoming reddish-brown after exposure. The root system consists of a strong taproot and well developed lateral roots.
The alternate, pinnate leaves are 20-40 cm long, with 20-31 medium to dark green leaflets about 3-8 cm long. The terminal leaflet is often missing. The petioles are short. Very young leaves are reddish to purplish in colour. The shape of mature leaflets is more or less asymmetric and their margins are dentate with the exception of the base of their basiscopal half, which is normally very strongly reduced and cuneate.
The flowers (white and fragrant) are arranged axillary, normally more-or-less drooping panicles which are up to 25 cm long. The inflorescences, which branch up to the third degree, bear 150-250 flowers. An individual flower is 5-6 mm long and 8-11 mm wide. Protandrous, bisexual flowers and male flowers exist on the same individual (polygamous).
The fruit is a glabrous olive-like drupe which varies in shape from elongate oval to nearly roundish, and when ripe are 1.4-2.8 x 1.0-1.5 cm. 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 inner shell (endocarp) of the fruit encloses one, rarely two or three, elongated seeds (kernels) having a brown seed coat.
The neem tree is very similar in appearance to the Chinaberry, all parts of which are extremely poisonous.
In India, the tree is variously known as "Divine Tree," "Heal All," "Nature's Drugstore," "Village Pharmacy" and "Panacea for all diseases." Products made from neem have proven medicinal properties, being anthelmintic, antifungal, antidiabetic, antibacterial, antiviral, anti-infertility, and sedative. It is considered a major component in Ayurvedic medicine and is particularly prescribed for skin disease.
Neem is a source of environment-friendly biopesticides.. The unique feature of neem products is that they do not directly kill the pests, but alter the life-processing behavior in such a manner that the insect can no longer feed, breed or undergo metamorphosis. However, this does not mean that the plant extracts are harmful to all insects. Since, to be effective, the product has to be ingested, only the insects that feed on plant tissues succumb. Those that feed on nectar or other insects such as butterflies, bees, and ladybugs hardly accumulate significant concentrations of neem products.
The oil is also used in sprays against fleas in cats and dogs.
The tender shoots and flowers of the neem tree are eaten as a vegetable in India. Neem flowers are very popular for their use in Ugadi Pachadi (soup-like pickle)which is made on Ugadi day in South India. A souplike dish called Veppampoo Rasam (translated as 'juice of neem flower') made of the flower of neem is prepared in Tamil Nadu. leaf or bark is considered an effective pitta pacifier due to its bitter taste. Hence, it is traditionally recommended during early summer in Ayurveda (i.e. month of chaitra as per Hindu Calendar which usually falls in month of March - April ). And during Gudi Padva which is the New Year in the state of Maharashtra, we find an ancient practice of drinking a small quantity of Neem juice or paste on that day before starting festivities. Like many Hindu festivals and their association with some food to avoid negative side-effects of that season or season change, neem juice is associated with Gudi Padva to remind people of using it during that particular month or season to pacify summer pitta.
Neem is also used in parts of mainland Southeast Asia, particularly in Cambodia and Thailand (where it is known as sadao or sdao), Laos (where it is called kadao) and Vietnam .Even lightly cooked, the flavour is quite bitter and thus the food is not enjoyed by all inhabitants of these nations, though it is believed to be good for one's health. Neem Gum is a rich source of protein.