Azadirachta indica

Neem is a fast-growing tree that can reach a height of 15–20 metres (49–66 ft), and rarely 35–40 m (115–131 ft). It is deciduous, shedding many of its leaves during the dry winter months. The branches are wide and spreading. The fairly dense crown is roundish and may reach a diameter of 20–25 m (66–82 ft). The neem tree is similar in appearance to its relative, the chinaberry (Melia azedarach).[4]

The opposite, pinnate leaves are 20–40 cm (8–16 in) long, with 20 to 30 medium to dark green leaflets about 3–8 cm (1+1⁄4–3+1⁄4 in) long. The terminal leaflet often is missing. The petioles are short.

White and fragrant flowers are arranged in more-or-less drooping axillary panicles which are up to 25 cm (10 in) long. The inflorescences, which branch up to the third degree, bear from 250 to 300 flowers. An individual flower is 5–6 mm (3⁄16–1⁄4 in) long and 8–11 mm (5⁄16–7⁄16 in) wide. Protandrous, bisexual flowers and male flowers exist on the same individual tree.

The fruit is a smooth (glabrous), olive-like drupe which varies in shape from elongate oval to nearly roundish, and when ripe is 14–28 mm (1⁄2–1+1⁄8 in) by 10–15 mm (3⁄8–5⁄8 in). The fruit skin (exocarp) is thin and the bitter-sweet pulp (mesocarp) is yellowish-white and very fibrous. The mesocarp is 3–5 mm (1⁄8–1⁄4 in) thick. The white, hard inner shell (endocarp) of the fruit encloses one, rarely two, or three, elongated seeds (kernels) having a brown seed coat.

Pollen grains of Azadirachta indica

The neem tree is often confused with a similar looking tree called bakain. Bakain also has toothed leaflets and similar looking fruit. One difference is that neem leaves are pinnate but bakain leaves are twice- and thrice-pinnate.

Neem (नीम/نیم) is a Hindustani noun derived from Sanskrit Nimba (निंब).[5][6][7]

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 of 400–1,200 mm (16–47 in). It can grow in regions with an annual rainfall below 400 mm, but in such cases it depends largely on ground water levels. Neem can grow in many different types of soil, but it thrives best on well drained deep and sandy soils. It is a typical tropical to subtropical tree and exists at annual mean temperatures of 21–32 °C (70–90 °F). It can tolerate high to very high temperatures and does not tolerate temperature below 5 °C (41 °F). Neem is one of a very few shade-giving trees that thrive in drought-prone areas e.g. the dry coastal, southern districts of India and Pakistan. The trees are not at all delicate about water quality and thrive on the merest trickle of water, whatever the quality. In India and tropical countries where the Indian diaspora has reached, it is very common to see neem trees used for shade lining streets, around temples, schools and other such public buildings or in most people's back yards. In very dry areas the trees are planted on large tracts of land.

Neem fruit, seeds, leaves, stems, and bark contain diverse phytochemicals, some of which were first discovered in azadirachta seed extracts, such as azadirachtin established in the 1960s as an insect antifeedant, growth disruptor, and insecticide.[11][12] The yield of azadirachtin from crushing 2 kg of seeds is about 5 g.[11]

In addition to azadirachtin and related limonoids, the seed oil contains glycerides, diverse polyphenols, nimbolide, triterpenes, and beta-sitosterol.[11][13] The yellow, bitter oil has a garlic-like odor and contains about 2% of limonoid compounds.[11] The leaves contain quercetin, catechins, carotenes, and vitamin C.[11]

Neem tree farm from south India

A large tree

Leaves

Bark

Neem seeds

Neem leaves are dried in India and placed in cupboards to prevent insects eating the clothes, and also in tins where rice is stored.[12] The flowers are also used in many Indian festivals like Ugadi. See below: #Association with Hindu festivals in India.

In March 2020, false claims were circulated on social media in various Southeast Asian countries and Africa, supporting the use of neem leaves to treat COVID-19. The Malaysian Ministry of Health summarized myths related to using the leaves to treat COVID-19, and warned of health risks from over-consumption of the leaves.[23] There is no evidence for the effectiveness of neem leaves in the treatment of COVID-19.[24]

Neem genome and transcriptomes from various organs have been sequenced, analyzed, and published by Ganit Labs in Bangalore, India.[25][26][27]

ESTs were identify by generation of subtractive hybridization libraries of neem fruit, leaf, fruit mesocarp, and fruit endocarp by CSIR-CIMAP Lucknow.[28][29]

Neem tree at Sant Nenuram Ashram, Pakistan

The name Nimai ('born under a neem tree'), of the Bhakti movement Vaishnava saint and Chaitanya Mahaprabhu (believed to be an incarnation of Radha Krishna in Gaudiya Vaishnavism and ISKCON) is due to his birth under a neem tree.

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 W. R. Grace and Company.[30] The Indian government challenged the patent when it was granted, claiming that the process for which the patent had been granted had been in use in India for more than 2,000 years. In 2000, the EPO ruled in India's favour, but W. R. Grace appealed, 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.[30]

The biopesticide produced by extraction from the tree seeds contains limonoid triterpenes.[11] Currently, the extraction process has disadvantages such as contamination with fungi and heterogeneity in the content of limonoids due to genetic, climatic, and geographical variations.[31][32] To overcome these problems, production of limonoids from plant cell suspension and hairy root cultures in bioreactors has been studied,[33][34] including the development of a two-stage bioreactor process that enhances growth and production of limonoids with cell suspension cultures of A. indica.[35]

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  Flowers
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  Unripe fruit
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  Neem tree in a banana farm in India
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  Neem tree farm
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  Twigs for sale
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  Fruit drying for oil extraction
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  Cleaning teeth by chewing stick
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  Native of Chhattisgarh with Neem branches and leaves for Hareli Festival
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  A tree in Gambia
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  A tree in Bangladesh

Wikimedia Commons has media related to Azadirachta indica.

• National Research Council (US) Panel on Neem (1992). Neem: A Tree For Solving Global Problems. National Research Council (US) Panel on Neem. doi:10.17226/1924. ISBN 978-0-309-04686-2. PMID 25121266. PDF Copy
• Invasiveness information from Pacific Island Ecosystems at Risk (PIER)
• Neem information from the Hawaiian Ecosystems at Risk project (HEAR)
• Caldecott, Todd (2006). Ayurveda: The Divine Science of Life. Elsevier/Mosby. ISBN 978-0-7234-3410-8. Archived from the original on 29 December 2010. Retrieved 15 January 2011. Contains a detailed monograph on Azadirachta indica (Neem; Nimba) as well as a discussion of health benefits and usage in clinical practice.

• Azadirachta indica in West African plants – A Photo Guide.