Azadirachta indica A.Juss.

Tree to 16 m; bole to 60 cm diam. Bark red-brown or greyish, fissured and flaking in old trees; inner bark red-brown with colourless, sticky foetid sap; sapwood whitish. Leafy twigs c. 4–8 mm, cicatrose, with pale vertical lenticels, garlic-scented when dam-aged. Leaves 15–35 cm, imparipinnate or paripinnate with terminal spike, 4–7-jugate, red when young, garlic-scented when damaged; petiole c. 3–7 cm, c. 1.5 mm diam., subglabrous, base weakly swollen. Leaflets opposite to subopposite, 5–9 by 1.5–3.5 cm, the subapical the largest, falcate-lanceolate, curved basipetally, subglabrous, bases very asymmetric, acute, apices long-acuminate, margin serrate, costae c. 15 on each side, obtuse, spreading; petiolules c. 1–2 mm. Thyrses to 30 cm, lax, paniculiform, axillary or in axils of fallen leaves, sweetly scented; axis c. 1.5 mm diam., subglabrous; branches to c. 15 cm, squarrose, bearing branchlets to 2 or 3 more orders, tipped with cymules of 1–3 flowers, finely sericeous; bracts and bracteoles c. 0.5–1 mm, lanceo-late, ± pubescent; pedicels c. 2 mm, swollen at articulation with pseudopedicel, c. 2.5–4 mm, finely pubescent. Calyx c. 1 mm long, salveriform, the lobes rounded, pubescent, margins ciliate. Petals linear spathulate, 4–6 mm long, white, ± pubescent on both sur-faces. Staminal tube glabrous to sparsely pubescent, 10-ribbed, margin with 10 rounded or somewhat laciniate lobes; anthers 10, c. 0.8 mm long, narrowly ellipsoid, basifixed, weakly exserted. Ovary glabrous to finely pubescent. Drupe c. 1–2 cm long, ellipsoid, green becoming yellow when ripe; mesocarp thin, fleshy.

A tropical plant. It occurs in most of Africa in both wet and dry areas. It grows in the Sahel. It originally comes from India. They can stand temperatures up to 49°C. Temperatures below freezing kill the plant. In Africa trees mostly grow between 50 an 1500 m altitude. They do best in dry subtropical climates. It will grow on dry shallow soils but grows on most kinds of soils. It can grow in soils with pH of 5 but does best with pH of 6.2. It can grow in arid places. It suits hardiness zones 11-12.

UsesSee also the paragraph on Phytochemistry, p. 8. Held sacred by the Hindus, the neem is potentially one of the most important of all tropical seasonal forest trees, having proved to be very adaptable and able to withstand arid conditions. It can be grown in impoverished soil and is a fastgrowing source of fuel wood [Ruskin, l.c.; see also M. Jacobson Focus on phytochemical pesticides vol. 1 1988 ; M. Jacobson Ad hoc panel of Nat. Res. Counc, Neem — a tree for solving global problems 1992 ;Tewari, l.c.]. The form grown in West Africa is ignored by stock and is therefore readily establish-ed. Some forms in Asia, however, are used as fodder and in the Malay Peninsula the young leaves and flowers are boiled and eaten with rice (Corner, l.c.). In Central Amer-ica, it is now widely planted and recent trials have shown it to grow rapidly and produce fine timber which makes a good substitute for Swietenia mahogany [ Pennington Fl. Neotropica 28 1981 25 ]. It is the most important plantation species in northern Nigeria and is used as poles or for fuel. It coppices well and the timber has a very high calorific value. Coppice shoots may reach 10 m height in two years. The wood is tougher than teak and resists decay. It is also widely planted as a windbreak, shade and avenue tree, the world’s biggest plantation being of 50,000 trees in the plains of Saudi Arabia, plant-ed to shade the two million or so Muslim pilgrims camping there annually for ‘Haj’ rites [ Sallem Ahmed et al. Econ. Bot. 43 1989 35 ]. It is a soil ameliorant and is potential-ly a source of many valuable by-products (Radwanski & Wickens, l.c.). It has been an ingredient of soaps, toothpaste and lotions in commerce for some decades (Corner, l.c.). The seeds contain some 40% oil by weight and this bitter material has been used in lamps and as a lubricant and has potential as a fuel-source, the mesocarp being a prom-ising substrate for the production of methane gas. Neem cake is an excellent fertilizer and the leaves and twigs are used as a mulch in Asia. The bark produces a valuable gum and tannin worth exploiting. The pressed leaves have long been put in books to ward off insects, the repellent being the limonoid, aza-dirachtin, which is in the seeds as well as the leaves; house-sparrows in India incor-porate leaves into their nests, perhaps reducing parasite loads. Azadirachtin is absorbed by plants and acts as a systemic insecticide so efficient that Japanese beetles and other insects, even including the desert locust, will starve rather than eat plants treated with it. It has been alleged that the substance is repellent to nematodes as well (Ruskin, l.c.). Of the many limonoids known from the tree, deacetylaxadirachnol (salannin) is as potent as azadirachtin in inhibiting ecdysis in tobacco budworm [ Kubo et al. Tetrahedron 42 1986 489 ]. Neem seed powder with carbofuran greatly reduces leaf-hoppers and rice tungro) virus in rice [ Kareem et al. Int. Rice Res. Newsl. 13 1988 35 ]. Reduction in the incidence of phloem-specific tungro viruses in neem-treated plants is attributed to a shift in insect-feeding from phloem to xylem vessels [ Saxena et al. J. Econ. Entom. 80 1986 1079 ]. Neem is alleged to contain anti-culicid factors and may be effective in controlling the spread of malaria. Under the Sanskrit name nimba it is mentioned in the Ayurvedae (Systema Medicinae) of Susruta, one of the most ancient of the Hindu medical writings. The first European account was published by Garcia d’Orta, physician to the Portuguese Viceroy at Goa in India, in 1563. The leaves, bark and seed oil have medicinal proper-ties summarized by Perry Med. Pl. E & SE Asia 1980 260 , and have been used in the treatment of a wide range of ailments, including malaria, eczema, dysentery and ulcers, but is particularly effective as a parasiticide for skin diseases such as scabies. Nimbidin, a substance isolated from the seed oil, has been found to be an efficient anti-inflamma-tory agent in artificially induced arthritis and oedema in rats [ Pillai & Santhakumari Pl. Medica 43 1981 59 ], while an aqueous extract of the bark has been shown to increase lymphocyte function such that production of MIF, a lymphokine, is increased, which may account for the generally stimulating and skin-healing properties long observed [ Van der Nat et al. J. Ethnopharmacol. 19 1987 125 ]. Some of the triterpenoids have antibacterial activity [ Siddiqui et al. J. Nat. Prod. 55 1992 303 ]. Neem oil also has significant post-coital contraceptive action [ Sinha et al. Ind. J. Med. Res. 79 1984 131 ].

Trees can be grown from seed. Seed need to be fresh as they only remain viable for 1-2 weeks. Seeds planted in nurseries need to have roots pruned off regularly. Seedlings can be planted out after 14-18 weeks. A spacing of 5 x 10 m is suitable. Fruit fall naturally during the rainy season.