Morus nigra L.

Millettia thonningii is a deciduous tree that can attain a height of up to 20 m and a short bole of diameter up to 1 m with a dense crown. Bark smooth, grayish and thin, when slashed shows creamy yellow. Leaves pinnate (simple-compound) with a slender, glabrous common stalk, 10-15 cm long and 3-4 pairs of opposite leaflets with terminal leaflet 6-10 cm long and 2.5-5.5 cm broad, elliptic or obovate, shortly acuminate with blunt tip or slightly notched, cuneate at base. The lower leaflets are progressively more rounded at the base, glabrous above, minutely hairy or glabrous beneath except for the characteristic brush of stiff white hairs at each side of the mid rib at the base with about 6 pairs of thin, up-curving lateral nerves running out very close to the margin. The lower leaflets are ovate or ovate-elliptic about 4-7 cm long and 2-4 cm wide. Flowers are blue, mauve or purple, 1.5 cm long, becoming paler as they expand, arranged singly or in pairs along a glabrous central stalk, 12-22 cm long pendulous among newly forming leaves. The racemes sometimes are grouped in terminal panicles. Individual flowers have slender, slightly hairy stalk 6-12 mm long with a pair of very small but conspicuous linear bracteoles half way up. Fruit is a dehiscent pod, 12-15 cm long and 18-25 mm broad, with more or less parallel margins or slightly broader towards the apex, sharply beaked, cuneate at the base, glabrous, smooth, flat and woody, usually containing 3-6 discoid black seeds about 10 mm across. The generic name is after C. Millet, c.1830, an officer of the East Indian company.

Flowering occurs between November and March. The fruiting season is between March and November, however fruits are ready for collection around the end of November.

M. nigra like a warm, well-drained soil, preferably a deep loam. Shallow soils such as those frequently found on chalk or gravel are not recommended.

This is a savanna and secondary forest species, often found on riverbanks. M. thonningii occurs as clumps or thickets on plains usually associated with termitaria belonging to the genus macrotermes.

M. thonningii is often cultivated on farmlands as a living fence or as avenue tree in cities.

Production of shoot from the lateral roots facilitates vegetative propagation through root cuttings.

The tree can be grown in various forms: as a tall standard with 1.8 m stem, as a low standard on a 0.9 m stem, as a bush, or as a pyramid-shaped tree. It can also be fan-trailed against a wall and is a good subject for pot cultivation. Standard trees require no pruning except for removing dead wood and thinning branches. Most forms, especially pyramid trees, need to have the lateral growth shortened to about 6 leaves to form spurs. Wall trees need to have their branches trained 30 cm apart. It is not advisable to prune the trees heavily due to the plant’s inclination to bleed—cuts of more than 5 cm in diameter generally do not heal and should be avoided. The bleeding will be less severe if the tree is pruned while it is dormant. Trees grow very rapidly, need full sun, adequate space (at least 4.5 m between each tree) and generally thrive with minimal fertilization. Although somewhat drought resistant, they need to be watered in the dry season; if the roots become too dry, the fruit are likely to drop before being fully ripened. Pot trees need repotting each year before new growth commences. They are not easily killed, and careful pruning and cultivation have rejuvenated old specimens. Broken, undetached branches usually take root if they touch the ground.

M. nigra is generally free of pests and diseases, although cankers and die-back can occur. A white powdery coating on the lower leaf surface is a symptom of mildew spread by the pathogens Phyllactinia corylea and Uncinula geniculata. It can be treated with sulphur dust, copper oxychloride, karathane and imazalil. In some areas, ‘popcorn disease’, in which the fruit swells to resemble popped corn, is an occasional problem. The disease carries over from one season to the next, so collecting and burning infected fruit help control it.

Seed storage behaviour is orthodox, long-term storage at IITA Genebank.

Erosion control: Production of heavy litter by M. thonningii coupled with a network of lateral roots makes it good for soil conservation and erosion control especially on sloping ground. Shade or shelter: The tree produces leaves heavily, hence when in leaf provides shade on avenues. Nitrogen fixing: The tree has nodulation and nitrogen fixing ability. Soil improver: Leaves are shed in large quantity during the dry season and serve as mulch. Ornamental: Because of its flowers that appear in the dry season as well as the dark green foliage, it is often cultivated as an avenue tree or as a living fence.

Fodder: Both cattle and sheep consume leaves of M. thonningii. Apiculture: Flowers provide nectar in the dry season for bees and this potential can be utilized for honey production. Fuel: The wood and the woody dry pods which drop after releasing the seeds are a source of fuelwood. Timber: The sap wood is yellowish-white with a darker greenish brown heartwood, heavy and fine grained, very hard, flexible and polishes well. It is used to make handles for implements such as axes, knives, tools, and the flexible young branches are used in construction of huts yam stakes, fencing poles and making traps. Poison: Leaf juice is poisonous and is used to poison water snails. Medicine: Root and bark decoctions are used for worms expulsion and as laxative, while the boiled pulverized roots and the bark are used for blood purification. Leaf extract is used for diarrhoea or dysentery and a decoction of the bark is purgative.