Neem is a fast growing tree that can reach a height of 15-20 m, rarely to 35-40 m. 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. Protandric and 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.
But Neem is far more than a tough tree that grows vigorously in difficult sites. Among its many benefits, the one that is most unusual and immediately practical is the control of farm and household pests. Some entomologists now conclude that neem has such remarkable powers for controlling insects that it will usher in a new era in safe,natural pesticides.
The neem tree is noted for its drought resistance. Normally it thrives in areas with sub-arid to sub-humid conditions, with an annual rainfall between 400 and 1200 mm. It can grow in regions with an annual rainfall below 400 mm, but in such cases it depends largely on the ground water levels. Neem can grow in many different types of soil, but it thrives best on well drained deep and sandy soils (pH 6.2-7.0). It is a typical tropical/subtropical tree and exists at annual mean temperatures between 21-32 °C. It can tolerate high to very high temperatures. It does not tolerate temperature below 4 °C (leaf shedding and death may ensue).
Cultivation and uses
Neem has been introduced into cultivation over wide areas of Asia, Africa, the Americas, Australia and the islands of the south Pacific. It is present mainly in the drier (arid) tropical and subtropical zones. Mountainous areas are generally avoided.
The beneficial properties of the neem tree have been part of Indian folklore for thousands of years. Dubbed 'the village pharmacy', it has numerous medicinal properties, aiding conditions ranging from digestive disorders to diabetes and from high cholesterol to cancer. In some parts of Sub-Saharan Africa the bark is used as both toothbrush and toothpaste, and for treating malaria. For many of the medicinal properties mentioned, no scientific data exists, but the fame is based on traditional knowledge (Ayurvedic medicine) or anecdotal stories. All parts of the tree (seeds, leaves, flowers and bark) are used for preparing many different
Of primary interest to research scientists is its activity as an insecticide. Many of the tree's secondary metabolites have biological activity, but azadirachtin is considered to be of the most ecological importance. Studies have shown a wide spectrum of activity and species affected. It acts by breaking the insect's lifecycle. Research has increased in the past few years as the desire for safe pest control methods increases and it becomes apparent that this tree will be able to play a role in integrated pest management systems.
Neem is deemed very effective in the treatment of scabies although only preliminary scientific proof exists which still has to be corroborated, and is recommended for those who are sensitive to permethrin, a known insecticide which might be irritant. Also, the scabies mite has yet to become resistant to neem, so in persistent cases neem has been shown to be very effective. There is also anecdotal evidence of its effectiveness in treating infestations of head lice in humans.
The tender shoots of the neem tree are eaten as a vegetable in parts of mainland Southeast Asia, particularly in Cambodia (where it is known as sadao or sdao), Laos (where it is called kadao) and Vietnam (where it is called sầu đâu). Even lightly cooked, the flavor is quite bitter and thus the food is not enjoyed by all inhabitants of these nations, though it is believed to be quite healthful.
In 1995 the European Patent Office (EPO) granted a patent on an anti-fungal product, derived from neem, to the United States Department of Agriculture and multinational WR Grace. The Indian government challenged the patent when it was granted, claiming that the process for which the patent had been granted had actually been in use in India for over 2000 years. In 2000 the EPO ruled in India's favour but the US multinational mounted an appeal claiming that prior art about the product had never been published in a scientific journal. On 8 March 2005, that appeal was lost and the EPO revoked the neem patent. Other aspects of neem use continue to be patented, not least in India itself.
Other useful herb information: Bloodroot | Red Clover | Gugulipid | Wormwood | Essiac | Goldenseal | Nutmeg
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