Solenostemon rotundifolius

Family

Lamiaceae (Labiatae)

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Chromosome number

2n = 64, 84

Synonyms

Germanea rotundifolia Poir. (1812), Plectranthus ternatus Sims (1824), Plectranthus rotundifolius (Poir.) Spreng. (1825), Coleus dysentericus Baker (1894), Coleus rotundifolius (Poir.) A.Chev. & Perrot (1905).

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Vernacular names

Hausa potato, frafra potato, Sudan potato, coleus potato, Zulu round potato (En). Pomme de terre de Madagascar, pomme de terre du Soudan (Fr).

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Origin and geographic distribution

Solenostemon rotundifolius originates from tropical Africa, where it is still found in the wild in East Africa. It was widely cultivated in the savanna region from Senegal to western Sudan and in South Africa, but nowadays there are only relics of former cultivation in Mali, Ghana, Nigeria and South Africa. As a crop it is now more important in tropical Asia.

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Uses

The tasty tubers of Hausa potato are eaten as a relish with a starchy staple food, but occasionally they constitute the staple food. They are cooked with spices in various combinations with other foods such as beans and cooked vegetables. They are often roasted and people eat them whole, including their skin, as a snack. In northern Ghana farmers use them to bridge the hunger gap between planting and harvest of the main staple crops. The tubers are made into alcoholic drinks. The leaves are occasionally used as a potherb, but more often in traditional medicine, e.g. for the treatment of dysentery in Nigeria. The plant is also used to treat blood in the urine as well as eye disorders. It has various sociocultural uses. Stems from harvested plants can be used as bedding material for livestock and later turned into farmyard manure.

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Production and international trade

Hausa potato has declined considerably in importance both as a starchy vegetable and as a staple crop; it has been replaced by higher-yielding starch crops such as cassava and sweet potato. It can still be found in cultivation in the Kita region in Mali, the northern districts of Ghana, the Jos Plateau in Nigeria, and northern and eastern parts of South Africa. Production data are not available. International trade has been reported to take place between northern Ghana and Burkina Faso.

Properties

The composition of the raw tubers per 100 g edible portion is: water 75.6 g, energy 394 kJ (94 kcal), protein 1.3 g, fat 0.2 g, carbohydrate 21.9 g, fibre 1.1 g, Ca 17 mg, Fe 6.0 mg, thiamin 0.05 mg, riboflavin 0.02 mg, niacin 1.0 mg, ascorbic acid 1 mg (Leung, W.-T.W., Busson, F. & Jardin, C., 1968).

Description

Perennial, semi-succulent, aromatic herb up to 40(–60) cm tall, branched, producing ovoid tubers up to 4(–8) cm long; stem erect to decumbent, 4-angled, shortly pubescent. Leaves opposite, simple; stipules absent; petiole 2–3 cm long; blade ovate, 2.5–8 cm × 2–5 cm, cuneate at base, obtuse to acute at apex, margin crenate-dentate, puberulous and gland-dotted below, distinctly veined. Inflorescence a terminal and slender false spike up to 15 cm long, consisting of compact, sessile dichasia. Flowers bisexual, zygomorphous; pedicel up to 1(–2) mm long; calyx campanulate, 1.5–3 mm long, glandular-hispid, upper tooth ovate, 2 lateral teeth small, 2 lower teeth almost completely fused; corolla 4–8 mm long, pubescent and gland-dotted, with curved tube, 2-lipped, upper lip erect, 4-lobed, whitish, lower lip boat-shaped, bluish purple; stamens 4, shortly united at base, curved within the lower corolla lip; ovary superior, 4-celled, style 2-fid. Fruit consisting of 4 nutlets, but rarely developing.

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Other botanical information

Solenostemon comprises some dozens of species and occurs in Africa and Asia. It is sometimes included in Plectranthus. Plectranthus in the strict sence differs in its calyx, of which the lower teeth are united at the base only, whereas the lateral teeth are more or less equal to the lower.
The Hausa potato is sometimes confused with other tuber-bearing Lamiaceae species, particularly Plectranthus esculentus N.E.Br. (Livingstone potato), which differs in its cylindrical stems, elongate tubers and larger, yellow flowers, and Plectranthus edulis (Vatke) Agnew (Ethiopian potato), which differs in its trailing stems rooting on the nodes, irregularly shaped tubers and ascending hairy inflorescences with bright blue flowers.
Tubers of Hausa potato can be found in a diversity of shapes, sizes and colours. Types with a grey to blackish brown tuber skin are found in Mali, whereas tubers with a skin colour ranging from pale yellow to dark red are found elsewhere in Africa. There are also wild types without tubers.

Growth and development

Tubers occur in clusters of 3–7, either at the base of the stem or at the nodes below the soil surface. They are ready for harvesting 150–200 days after planting by which time the plant has flowered and aerial parts have become senescent. Most tubers found in Africa are 2.5–4 cm × 1–1.5 cm, but some reach up to 8 cm. Such larger tubers are the norm in India and Sri Lanka, where yields are also higher than those in Africa’s semi-arid zones.

Ecology

Solenostemon rotundifolius occurs wild in grassland in East Africa, up to 2200 m altitude in Kenya. It is suited for cultivation in marginal areas in dry savanna with poor soils. However, tubers may not be formed when rain is insufficient. When there is too much rain, the tubers tend to branch, which is disliked by consumers because they are then difficult to peel. Hausa potato requires full sunlight and shade from other crops reduces yields. Tubers are formed with relative ease in sandy soil, but will not develop well in compacted heavy soil. Soils should be well drained as waterlogging is not tolerated.

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Propagation and planting

Hausa potato is normally propagated vegetatively by tubers, suckers or soft-woody stem cuttings because it produces few seeds despite the many flowers. Planting is done at the beginning of the rainy season either in mounds or ridges or in well-drained, loose soil on flat ground. In Ghana only sprouted tubers are planted with the growing end placed at the soil surface and not covered by soil. Burying will delay sprouting. Ridges are spaced at 90 cm and plants are spaced at 15–20 cm in the ridges, resulting in a plant density of about 50,000 plants/ha. In South Africa tubers are planted at a depth of 5–10 cm with a spacing of 25 cm on ridges spaced at 75 cm. Cuttings are used occasionally and planted in pairs facing opposite directions. They are placed at a depth of 5 cm, but with the growing point clearly above the soil surface. Farmers in Ghana apply wood ash and diluted cattle urine prior to planting to promote growth and development of the crop.
Experimental in-vitro multiplication by tissue culture was successful, using stem meristems, apices and nodes.

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Management

Hausa potato is grown either as a sole crop or intercropped with bambara groundnut, yam, okra, millet, maize or sorghum. Because of the comparatively low yields, people hardly apply manure or fertilizer. In Ghana, however, much better yields were obtained when a liberal application of organic material was incorporated into the ridges or mounds before planting, followed by a topdressing of NPK fertilizer (e.g. NPK 16–8–8 at a rate of 125 kg/ha). When the crop is well established, earthing up with loose soil is necessary for good tuber development. Irrigation may be required during the dry season for crops planted towards the end of the rainy season. Cultivation throughout the year is possible.

Diseases and pests

The incidence of pests and diseases in Hausa potato is generally low. Tuber rot, virus mottling and scab have been observed, as well as damage by termites, centipedes and potato weevils. Millipedes bore holes in the tubers. Grasshoppers and stem borers may attack the leaves. In South Africa it is believed that the crop suppresses nematode populations, but the Crop Research Institute in Kumasi, Ghana, has found that infestation by nematodes may lead to large yield losses, so that further research is needed. Where pigs roam freely these are the most serious pest.

Harvesting

When the leaves and stems dry out and tubers have reached maturity, the plants are harvested with their tubers still attached by gently excavating them. The tubers are then removed and packed in baskets or sacks. Tubers left in the soil are liable to rapid decay.

Yield

Tuber yields depend strongly on the amount and regularity of the rains. In Ghana, yields range between 5 and 15 t/ha when conditions are good, but are considerably lower when soil fertility or rainfall are poor. Experimental work carried out at Roodeplaat in South Africa has indicated that the potential yield could be up to 45 t/ha when adequate irrigation and plant nutrients are provided together with good agronomic practices.

Handling after harvest

Hausa potato is difficult to store. Traditionally the tubers are stored in the ground under a tree where it is cooler than in the open. When stored in this way under hot conditions the special taste of Hausa potato usually lasts for two months only, after which the tubers become bland and are no longer considered a delicacy. Hausa potato is also packed in bags or baskets stuffed with straw, but if these are kept under warm conditions the tubers will soon shrivel and are no longer edible. To keep the tubers longer, people put them in pots sealed with cow dung. The small tubers needed for the next planting season are stored in this way. In cooler conditions, such as in highland regions or in South Africa, storage is easier.

Genetic resources and breeding

Hausa potato has become a rare food crop in Africa. It also seems uncommon in the wild. However, there is still a wide diversity of both wild and cultivated germplasm throughout the African continent. The Vegetable and Ornamental Plant Institute, Pretoria, South Africa maintains germplasm collected in Malawi, Zambia and South Africa. A small germplasm collection is also held at the Plant Genetic Resources Centre in Bunso, Ghana. More elaborate collection of germplasm all over Africa is needed to maintain this traditional crop for future generations. Outside Africa collections are maintained at the Plant Genetic Resources Centre, Gannoruwa, Peradeniya, Sri Lanka and at the Central Tuber Crops Research Institute, Trivandrum, India.

Breeding

Very little breeding work on Hausa potato has been done. Breeding to increase the size of the tuber is highly desirable. Selection in seed-propagated populations may result in productive virus-free types.

Prospects

Hausa potato has good prospects as a delicate vegetable if cultural practices could be improved in combination with improved cultivars. However, as a vegetatively propagated crop it is of no interest to seed companies. Although as a starchy staple food Hausa potato cannot compete with cassava, yams and sweet potatoes, it may be of some interest for dryland regions with poor soils, where the choice of starchy crops is limited. Comparatively little is known about this crop and research is badly needed, not only concerning cultural practice but also taking into account wild populations.

Major references

• Agnew, A.D.Q. & Agnew, S., 1994. Upland Kenya wild flowers: a flora of the ferns and herbaceous flowering plants of upland Kenya. 2nd Edition. East Africa Natural History Society, Nairobi, Kenya. 374 pp.
• Allemann, J. & Coertze, A.F., 1997. Indigenous root crops. A3: Solenostemon. Vegetable and Ornamental Plant Institute, Pretoria, South Africa.
• Apabol, R.R., 1997. Assessment of the performance of some frafra potato (Coleus dysentericus Baker) accessions in Nyankpala area of Ghana. Dissertation, University of Development Studies, Nyankpala, Tamale, Ghana.
• Burkill, H.M., 1995. The useful plants of West Tropical Africa. 2nd Edition. Volume 3, Families J–L. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 857 pp.
• Codd, L.E., 1975. Plectranthus (Labiatae) and allied genera in Southern Africa. Bothalia 11(4): 371–442.
• Jansen, P.C.M., 1996. Plectranthus rotundifolius (Poiret) Sprengel. In: Flach, M. & Rumawas, F (Editors). Plant Resources of South-East Asia No 9. Plants yielding non-seed carbohydrates. Backhuys Publishers, Leiden, Netherlands. pp. 141–143.
• Kay, D.E. & Gooding, E.G.B., 1987. Root crops. 2nd Edition. Crops and Product Digest 2. Tropical Development & Research Institute, London, United Kingdom. 380 pp.
• Miège, J. & Moncousin, C., 1989. Deux espèces à tubercules comestibles menacées de disparition: Solenostemon rotundifolius et Plectranthus esculentus (Lamiacées). Possibilité de leur conservation par micropropagation. Bulletin de la Société Botanique de France 136: 185–193.
• Schippers, R.R., 2000. African indigenous vegetables. An overview of the cultivated species. Natural Resources Institute/ACP-EU Technical Centre for Agricultural and Rural Cooperation, Chatham, United Kingdom. 214 pp.
• Tetteh, J.P. & Guo, J.I., 1993. Problems of frafra potato in Ghana. Dissertation, School of Agriculture, University of Cape Coast, Ghana.

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Other references

• Codd, L.E., 1985. Lamiaceae (Labiatae). In: Leistner, O.A. (Editor). Flora of southern Africa. Volume 28, part 4. Botanical Research Institute, Department of Agriculture and Water Supply, Pretoria, South Africa. 247 pp.
• Dupriez, H. & De Leener, P., 1989. African gardens and orchards, growing vegetables and fruits. MacMillan Press, London, United Kingdom. 333 pp.
• Harlan, J.R., De Wet, J.M.J. & Stemler, A.B.L., 1976. Origins of Africa plant domestication. Mouton, The Hague, Netherlands. 498 pp.
• Leung, W.-T.W., Busson, F. & Jardin, C., 1968. Food composition table for use in Africa. FAO, Rome, Italy. 306 pp.
• Murdock, G.P., 1959. Africa, its people and their culture history. MacCraw-Hill Book Company, New York, United States. 456 pp.
• Tindall, H.D., 1983. Vegetables in the tropics. Macmillan Press, London, United Kingdom. 533 pp.
• van Wyk, B.E. & Gericke, N., 2000. People’s plants: a guide to useful plants of southern Africa. Briza Publications, Pretoria, South Africa. 351 pp.

Afriref references

Sources of illustration

• Jansen, P.C.M., 1996. Plectranthus rotundifolius (Poiret) Sprengel. In: Flach, M. & Rumawas, F (Editors). Plant Resources of South-East Asia No 9. Plants yielding non-seed carbohydrates. Backhuys Publishers, Leiden, Netherlands. pp. 141–143.

Author(s)

•	G.O. Nkansah Faculty of Agriculture, ARS-KADE, University of Ghana (Legon), P.O. Box 55, Accra (Legon), Ghana

Editors

•	G.J.H. Grubben Boeckweijdt Consult, Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
•	O.A. Denton National Horticultural Research Institute, P.M.B. 5432, Idi-Ishin, Ibadan, Nigeria

Associate editors

•	C.-M. Messiaen Bat. B 3, Résidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
•	R.R. Schippers De Boeier 7, 3742 GD Baarn, Netherlands

General editors

•	R.H.M.J. Lemmens PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
•	L.P.A. Oyen PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Photo editor

•	E. Boer PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article

Nkansah, G.O., 2004. Solenostemon rotundifolius (Poir.) J.K.Morton. [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 .

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