Polygala butyracea (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Cereal / pulse|
Polygala butyracea Heckel
- Protologue: Bull. Geogr. 13: 222 (1889).
- Family: Polygalaceae
Origin and geographic distribution
Polygala butyracea is only known as a cultivated and naturalized plant. It has a fairly wide, disjunct distribution which may be the result of a more widespread area of ancient cultivation that has been contracting since. There used to be 3 centres of cultivation: the first from Guinea Bissau to western Côte d’Ivoire; the second in northern Togo and Benin and the third in northern Cameroon and adjacent areas in Nigeria and the Central African Republic. Records for Ghana are substantiated by herbarium vouchers and for Gabon it is mentioned in a single source but there are no herbarium vouchers. The introduction of groundnut (Arachis hypogaea L.), sesame (Sesamum indicum L.) and black sesame (Hyptis spicigera Lam.) in Africa is probably responsible for the gradual disappearance of Polygala butyracea as a crop.
In Cameroon, Nigeria, Central African Republic and Gabon Polygala butyracea is primarily grown for its bark fibre. In Nigeria the fibre is made into thread used for weaving bags and cloth and producing fishing lines and nets. In Gabon the fibre is used for making cordage, while the seed is used as an expectorant. From Benin westwards Polygala butyracea is mainly grown for the seed oil or fat that is used for cooking. The fat is known as ‘cheyi fat’, ‘malukang butter’ and ‘ankalaki butter’. The seeds are heated or fried and ground and the resulting dry, yellow meal is added to foods such as soups and meat dishes.
The fibre of Polygala butyracea is similar to that of sunn hemp (Crotalaria juncea L.). Mature and dried seed contains up to 59% oil and 10% protein. The oil is pale yellow and has a nutty flavour. The fatty acid composition of the seed oil is: palmitic acid 62%, oleic acid 32% and myristic acid 6%. The oil also contains phospholipids (1.5%).
Annual (or perennial) herb 200–270 cm tall, single-stemmed or weakly branched, stems soft hairy. Leaves alternate, entire; blade linear, acute at apex, 8–16 cm × 0.5–1 cm, midrib prominent. Inflorescence a long, terminal raceme, subtended by a persistent bract, 3–5 mm long, bracteoles 2, 1–2 mm long. Flowers bisexual, zygomorphic, white, creamy to pinkish; pedicel 2.5–3 cm long; sepals 5, free, persistent, unequal, 2 inner ones largest, petaloid, c. 10 mm × 6 mm, glabrous on the outside; petals 3, 2 upper ones basally fused with staminal tube, lower one boat-shaped (keel), clawed; stamens 8, monadelphous, anthers basally attached, opening with a terminal pore; ovary laterally compressed, 2-celled, each locule with 1 ovule. Fruit an elliptical capsule c. 8 mm long, compressed, narrowly winged, dehiscing by a marginal split. Seed c. 6 mm long, dark, glabrous with hairs at top and bottom, at micropilar side with small caruncle. Seedling with epigeal germination; cotyledons ovate, rounded; first pair of leaves ovate to elliptical, reddish green.
Polygala is a cosmopolitan genus comprising about 750 species, with just over 200 species in tropical Africa. In a recent revision of the African species of Polygala, the genus is subdivided in subgenera, sections and subsections. Polygala butyracea is placed in Sativae, a subsection with 30 species. All Polygala species with a documented fibre use are placed in this subsection. Polygala cristata P.Taylor and Polygala baikiei Chodat are suggested as possible ancestors of Polygala butyracea. Polygala cristata differs by its considerably smaller, hairy seeds, and it is only known from Guinea, Sierra Leone, Liberia and Côte d’Ivoire. The name Polygala gomesiana has been misapplied for Polygala exelliana Troupin of which the bark fibres are used in south-western Tanzania for making twine and rope. In DR Congo the roots are cooked and eaten. It also occurs in Zambia and Malawi, and an infusion of the roots is used as a remedy for coughs. Polygala macrostigma Chodat is an annual herb more than 1 m tall, native to DR Congo, Uganda, Tanzania and Angola. In DR Congo the bark fibres are used for tying and for making cords, while the leaves and seeds are consumed. In Malawi the roots are chewed as a cure for coughs. The bark fibres of Polygala nambalensis Gürke, Polygala sparsiflora Oliv. (synonym: Polygala ukirensis Gürke) and Polygala usafuensis Gürke are used in DR Congo for making rope.
Polygala butyracea is restricted to cultivated fields up to 600 m altitude, and is occasionally found as an escape of cultivation. It grows fairly well on poor soils.
In Sierra Leone Polygala butyracea has been grown as a dry-season crop in rice fields. In Nigeria it is grown in a mixed cropping system with yams. When appearing as a weed in annual crops it is spared until the seeds are mature and can be harvested. Flowering of Polygala butyracea starts towards the end of the rainy season and continues for several months. As long as the plants remain green the seeds are not shattered. The uneven ripening of the seeds is a disadvantage for commercial cultivation for oil production.
As Polygala butyracea is restricted to cultivated fields (with occasional naturalization) and its cultivation is declining, it is likely to be threatened with genetic erosion. Germplasm collection and evaluation of Polygala butyracea, its assumed ancestors and other closely related species is long overdue.
It may be worthwhile to investigate possibilities for genetic improvement through selection and improvements in cultivation measures.
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- C.H. Bosch, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Correct citation of this article
Bosch, C.H., 2011. Polygala butyracea Heckel. [Internet] Record from PROTA4U. Brink, M. & Achigan-Dako, E.G. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 12 November 2020.
- See the Prota4U database.