Solanum americanum (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Forage / feed|
Solanum americanum Mill.
- Protologue: Gard. dict. ed. 8: Solanum No 5 (1768).
- Family: Solanaceae
- Chromosome number: 2n = 24
- Solanum nodiflorum Jacq. (1789),
- Solanum nigrum auct. non L.
- Glossy nightshade (En).
- Morelle noire (Fr).
- Erva moura, maria pretinha, pimenta de galinha, erva de bicho (Po).
- Mnavu mchungu (Sw).
Origin and geographic distribution
Solanum americanum is widespread, found throughout the tropics and subtropics, often in disturbed localities. Its closest relatives are found in South America and this might be the origin. However, the original range cannot be traced from the earliest collections and a few authors have speculated that the species originates from southern Europe and others that it originates from Australia.
Solanum americanum is recorded for many countries of tropical Africa. Unfortunately the Swahili name ‘mnavu’ and other local names refer to various species of the section Solanum. In Tanzania it is called ‘mnavu mchungu’ meaning bitter nightshade, but Solanum americanum is often only slightly bitter. It is reported as a cultivated leafy vegetable from Sierra Leone, the lowlands of Ethiopia, Kenya, Uganda, Tanzania, Seychelles and Mauritius. It is a popular wild pot herb in Côte d’Ivoire and Cameroon, and in eastern Zimbabwe and Mozambique the leaves are also eaten as a vegetable.
The shoots and younger leaves of Solanum americanum are boiled as a leafy vegetable. Depending on the bitterness, the cooking water is refreshed. This is done especially for children. Elderly people appreciate a higher degree of bitterness and will therefore leave the flowers and young fruits, whereas people who object to the bitter taste remove them. To further reduce the bitterness, the leaves are served together with cooked amaranth, either separately or as a mixture. In Uganda, the leaves are steamed and the juice is collected and used in soups, so that the nutrients are fully utilized.
Several other uses are reported for Solanum americanum, but this information may concern related species. It is believed that leaves cooked with milk, groundnut or sesame (Sesamum indicum L.) protect children from diseases associated with malnutrition. In Tanzania the juice extracted from the leaves is used to relieve chronic conjunctivitis and related inflammations. In Cameroon pounded leaves are used to treat sores. In Sierra Leone, people with heart pains use the leaves raw. In Nigeria fruits are used to treat worms in chicken; the fruits are soaked in water and the mixture is given to chicken to drink. In Brazil the leaves are used to treat skin problems. In most regions, Solanum americanum fruits are considered inedible but Kipsigis children in Kenya eat the ripe fruits and also in the border region between south-eastern Zimbabwe and Mozambique the sweet fruits of local varieties are much appreciated.
Production and international trade
Even though Solanum americanum can be found in many countries, its utilization is often limited to collection from the wild or cultivation in home gardens. Commercial production occurs occasionally in coastal lowlands and especially in the Indian Ocean islands. Its importance, compared with other species within the section Solanum such as Solanum scabrum Mill. and Solanum villosum Mill., is limited. No reliable statistics on production or trade are available.
The composition of Solanum americanum leaves is probably comparable to other dark-green leafy vegetables. The cooking water is sometimes replaced to reduce the bitter taste of some varieties and especially when leaves are collected from the wild. The bitterness is associated with a high content of the glycoalkaloid solanine, which is found throughout the plant with the highest concentration in the unripe fruits. In the leaves the concentration increases with age. Solanine is poisonous and only partially soluble in water. Eating a large amount of this vegetable has been associated with diarrhoea and cardiac arrest. Other alkaloids isolated from Solanum americanum are the steroids solasodine and diosgenin, with the highest concentration found in green fruits.
Adulterations and substitutes
In dishes Solanum americanum can be replaced by other species of the section Solanum, e.g. Solanum scabrum or Solanum villosum.
- Annual or short-lived perennial herb, erect and widely spreading, up to 150 cm tall, unarmed; stem rounded or narrowly winged, sometimes warty, glabrous or sparsely pubescent, young stem sometimes covered with curved, simple hairs.
- Leaves arranged spirally to almost opposite, simple; stipules absent; petiole 1–9 cm long; blade ovate to lanceolate, up to 14(–16) cm × 7(–12) cm, cuneate to truncate at base and decurrent along the petiole, acute to acuminate at apex, entire to toothed, glabrous or sparsely pubescent.
- Inflorescence an extra-axillary, umbel-like cyme, 3–10-flowered; peduncle 0.5–2.5 cm long, elongating up to 4 cm in fruit.
- Flowers bisexual, regular, 5-merous; pedicel 5–10 mm long, becoming nodding; calyx cup-shaped, 1.5–2 mm in diameter, lobes ovate to oblong, reflexed in fruit; corolla deeply stellate, 5–9 mm in diameter, white or flushed purple with basal yellow-green star, lobes ovate-oblong, c. 3 mm long; stamens inserted on corolla throat, filaments 0.5–2 mm long, with hairs on inner side, anthers connivent, 1.5–2 mm long, opening by terminal pores; ovary superior, globose, c. 1 mm in diameter, style 2.5–4 mm long, hairy in the lower part, stigma capitate, pale green.
- Fruit a globose berry 4–8(–10) mm in diameter, from green turning to glossy purplish black at maturity, rarely dark green, many-seeded.
- Seeds discoid, 1–1.5(–2) mm long, creamy coloured, often tinged with purple.
- Seedling with epigeal germination.
Other botanical information
Solanum americanum belongs to the subgenus Solanum and section Solanum, formerly known as section Maurella, or section or subsection Morella. Currently about 30 species are included in this section of which 10–12 are known to occur in Africa. Research is still needed to better understand the species within section Solanum and their diversity. The diversity within Solanum americanum is considerable and a thorough revision of this species may well reveal that several taxa are involved, especially when including material from other continents. In Africa the name Solanum nigrum is often used for almost all species of section Solanum with blackish fruits, including Solanum americanum. The confusion is aggravated by the use of vernacular names that refer to several species of this group. Solanum americanum is often confused with Solanum scabrum, but more robust stems, larger rounded leaves and larger fruits distinguish the latter.
Growth and development
After emergence of the seedling, growth is fast. Flowering starts about two months after germination. Solanum americanum is normally self-pollinating, but cross-pollination is possible by insects, mainly bees and syrphid flies. The plant continues to develop new flowers for several months. The fruits drop with the pedicel when fully ripe. They are eaten by birds, which disperse the seeds.
Solanum americanum is mainly found at low altitudes, often in coastal areas or near great lakes, e.g. Lake Victoria. Records from high altitudes may require further verification. It occurs mainly in humid areas on various soil types, in weedy plant communities in the open or in lightly shaded localities e.g. under trees. In semi-arid regions it is mostly found near a water source or as a weed in irrigated fields. It does not tolerate drought.
Propagation and planting
Solanum americanum is normally propagated by seed. The 1000-seed weight is about 0.5 g. The Giriama people in Kenya, however, propagate it by stem cuttings, selecting strong stems with or without leaves at the top for a new planting. Subsistence farmers sow seeds in pockets of up to 10 seeds at the beginning of the rainy season, as a sole crop or intercropped with other crops. For commercial purposes, seedlings for transplanting are produced in nurseries. The soil is loosened and enriched with decomposed manure in combination with wood ash. The seeds, in most cases mixed with sand or ash, are dispersed evenly over the soil surface or sown in rows and then mulched with grasses to prevent moisture loss from the soil. Transplanting may take place when the seedlings are about 15 cm tall, whereby only strong plants should be selected. The recommended spacing in pure stands is 30 cm × 30 cm, which could be reduced to 20 cm × 30 cm during the dry season. Spacing is normally wider during the rainy season to allow for sufficient air circulation, thus avoiding diseases. The spacing also depends on the size of the harvested shoots. When harvesting short shoots once per week, the planting density should be closer, while for harvesting larger shoots the spacing should be wider. In mixed plantings, the spacing depends on the other crops.
In cultivation Solanum americanum requires a fairly large amount of nutrients. Incorporating well-decomposed farmyard manure or compost into the soil prior to planting is recommended. When this is not available, compound fertilizers, for example NPK 20–10–10, may be used. Commercial farmers may apply nitrogen fertilizers as top dressings in the form of foliar sprays. Weeding and watering during dry periods are applied when needed.
Diseases and pests
The leaf fungus Cladosporium oxysporum and a yellow vein virus were observed to attack Solanum americanum in Nigeria. The species has been reported to be resistant to bacterial wilt but is susceptible to wilt caused by Verticillium dahliae. Black aphids, millipedes and snails have been reported as pests in Kenya, and variegated locust (Zonocerus variegatus), aphids and beetles (Epilachna hirta) in Nigeria. Farmers spread ash on the leaves to control insects, although various chemical pesticides are also used.
Leaves and stem tops are collected from plants in the wild, or from fields during the rainy season. Harvesting is normally done in the early morning. The main shoot or side shoots are plucked before flowering, leaving at least 5 cm of stem for the production of new side shoots. This method allows the farmer to harvest 6–8 times from the same plant. The farmer may select some superior plants which are not harvested but left for seed production.
Although no accurate records are available, the yield of Solanum americanum is probably comparable to that of Solanum villosum and Solanum tarderemotum Bitter since the plant structure and size, and the harvesting method are comparable. The yield can therefore be estimated at 10–20 t/ha, but with adequate management up to 50 t/ha would be feasible.
Handling after harvest
The shoots are very tender and therefore highly perishable. The produce is transported in jute bags and, where possible, sold on the same day. Once they arrive at the market, traders sprinkle the leaves with water to keep them fresh. When the product has to be kept for a longer period, it is covered with plastic or banana leaves to protect it from drying.
No specific germplasm collection of Solanum americanum is known to exist in Africa, but some accessions of the section Solanum are present in genebanks in Kenya, Tanzania and Zimbabwe. Correct identification of the accessions, however, is problematic. A large collection of Solanum americanum germplasm is present in the Solanum collection of the Botanical and Experimental Garden of Nijmegen University (Netherlands).
Solanum americanum is a potentially important leafy vegetable for the lowlands. Investigations are needed to reduce its alkaloid content, particularly of solanine, to make it safe and more palatable to consumers. Further research is needed into agronomic aspects, pest management and storage. There is also a need to develop appropriate cultivars to give farmers access to reliable sources of seed.
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- Edmonds, J.M., 1972. A synopsis of the taxonomy of Solanum section Solanum (Maurella) in South America. Kew Bulletin 27: 95–114.
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- Hunziker, A.T., 2001. Genera Solanacearum. The genera of Solanaceae illustrated, arranged according to a new system. A.R.G. Ganter Verlag Kommanditgesellschaft, Ruggell, Liechtenstein. 500 pp.
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Sources of illustration
- Hitchcock, C.L., Cronquist, A. & Ownbey, M., 1959. Part 4: Ericaceae through Campanulaceae. In: Hitchcock, C.L., Cronquist, A., Ownbey, M. & Thompson, J.W. (Editors). Vascular plants of the Pacific Northwest. University of Washington Press, Seattle, United States. 510 pp.
- Roe, K.E., 1971. Solanum L. In: Wiggins, I.L. & Porter, D.M. (Editors). Flora of the Galápagos Islands. Stanford University Press, Stanford, California, United States. pp. 478–482.
- M.L. Manoko, Botany Department, University of Dar es Salaam, P.O. Box 35060, Dar es Salaam, Tanzania
- G.M van der Weerden, Botanical and Experimental Garden, University of Nijmegen, Toernooiveld 11, 6525 ED Nijmegen, Netherlands
Correct citation of this article
Manoko, M.L. & van der Weerden, G.M., 2004. Solanum americanum Mill. [Internet] Record from PROTA4U. Grubben, G.J.H. & Denton, O.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 13 July 2021.
- See the Prota4U database.