Prota 14: Vegetable oils/Olιagineux
Linnaea 4: 314 (1829).
2n = 18
Centrapalus galamensis Cass. (1817), Vernonia pauciflora (Willd.) Less. (1829) non (Pursh.) Poir., Centrapalus pauciflorus (Willd.) H.Rob. (1999).
Ironweed, vernonia (En).
Origin and geographic distribution
Vernonia galamensis occurs naturally from Cape Verde and Senegal east to Eritrea and through East Africa south to Mozambique. The greatest diversity is found in East Africa, in West Africa only a single variety occurs. In the 1950s Vernonia anthelmintica (L.) Willd. was noted as a potential source of vernolic acid, but efforts to domesticate it have failed. In 1964 in semi-arid areas of eastern Ethiopia specimens of Vernonia galamensis were collected that combined a high vernolic acid content with a promising seed yield and good seed retention. Vernonia galamensis is now being developed as a potential industrial oil crop in several parts of the world.
Traditionally, Vernonia galamensis is considered a weed. The high oil content of the seed and the high content of vernolic acid in the oil make it a potential oil crop. The oil, called vernonia oil can be used in the chemical (glue, paint and plastics), pharmaceutical and agro-industrial industries. In the paint industry it is being tested as a component of low volatile-organic-solvent paints. As a component of heat-baked films and coatings, vernonia oil provides outstanding adhesion, flexibility and chipping resistance, and good resistance to alkaline, acid and non-polar solvents. In plastics it can be used as a plasticizer of PVC and as a structural component of polymers. The presscake is suitable as animal feed.
The leaves have been smoked as a substitute for tobacco in Ethiopia. In Tanzania the leaves are cooked in porridge, or drunk as a tea to treat chest pain. In Kenya the plant is used to treat stomach pain.
Production and international trade
Recently, commercial production of Vernonia galamensis has started in Ethiopia by Vernique Biotech. However, large-scale commercial production is still in its infancy and no data on production are available.
The seed contains per 100 g: 2027 g protein and 3645 g oil. The average fatty acid composition of seed-oil samples from Ethiopia is (ranges between brackets): vernolic acid 74% (3487%), palmitic acid 3% (28%), stearic acid 3% (17%), arachidic acid traces, oleic acid 5% (218%), linoleic acid 14% (735%). The presscake contains per 100 g: crude protein 44 g, crude fibre 11 g, ash 19 g, carbohydrate 7 g. The leaves contain a small amount of oil. The fatty acid composition of the leaf oil is: palmitic acid 1222%, linolenic acid 4159%, parinaric acid 817%; vernolic acid is only found in traces in the leaves.
Vernolic acid (cis-12,13-epoxy-cis- 9-octadecenoic acid or 12,13-epoxyoleic acid) is characterized by its chemically active epoxy group. Much of the vernolic acid occurs as the triglyceride trivernolin, which has a lower viscosity than chemically prepared epoxy-oils. Because of their chemical structure, vernolic acid and trivernolin can undergo chemical reactions characteristic of ester groups, double bonds and epoxy groups. The low viscosity of the oil makes it a solvent in alkyd-resin paints. It is non-volatile, but polymerizes and becomes part of the paint coat.
Adulterations and substitutes
Epoxy fatty acids for industrial purposes are mostly made industrially from petroleum products or from soya bean oil or linseed oil. Unless vernolic acid from Vernonia galamensis can be produced more cheaply, soya bean oil and linseed oil will remain the preferred raw materials for most purposes, but when low viscosity is required vernolic acid from Vernonia galamensis is economically more attractive than the more viscous epoxy oils derived from soya bean or linseed oil. Vernolic acid is present in smaller amounts in several other plants, bacteria and fungi. Apart from Vernonia anthelmintica, it was discovered in Stokesia laevis (Hill) Greene and Euphorbia lagascae Spreng. Efforts are underway to transfer genes encoding for a high vernolic acid content into Brassica and soya bean oil crops. However, the expression rate of the genes is much lower than in Vernonia galamensis and hence the economic potential of the transgenic crops is still not clear.
Usually annual herb up to 3(5) m tall, but mostly much smaller; stems ribbed, finely to coarsely hairy, sometimes branching near the top. Leaves alternate, rather crowded, simple, sessile; blade elliptical to linear, up to 25 cm Χ 5 cm, base cuneate, apex acuminate, margins toothed, hairy on both surfaces, but glabrescent. Inflorescence a head, solitary or few to many in a terminal, lax to rather dense, leafy cyme; peduncle stout, pubescent; involucre ovoid to nearly globose, 825 mm Χ 115 mm, involucral bracts in 46 rows, pale green often with darker tip, outer ones linear, short, middle ones often hardened at base, tips usually leaf-like, inner ones oblong to narrow-lanceolate and acuminate, somewhat dry membranous. Flowers normally bisexual and fertile, long exserted; corolla 7.516 mm long, lower half tubular, gradually expanding above, bright blue to pale mauve, pink, purple, violet or almost white, sometimes flushed pale yellow or green, lobes 5, linear, 27 mm long, glandular; stamens 5, slightly exserted, anthers united into a tube; ovary inferior, style exserted, 2-branched. Fruit a narrowly obovoid achene up to 8 mm long, with 10 equal, narrow ribs, dark brown to black, densely appressed hairy; pappus in 2 whorls, outer pappus of up to 2 mm long barbed bristles, inner pappus of up to 11 mm long barbed bristles.
Other botanical information
Vernonia comprises close to 1000 species. Most of them occur in South America; more than 300 species have been described from Africa with about one-third occurring in Madagascar and about 50 in Ethiopia. Recently it has been proposed that the Old World species of Vernonia be transferred to other genera; Vernonia galamensis then becomes Centrapalus pauciflorus (Willd.) H.Rob.
Vernonia galamensis is very variable; its centre of diversity is in Ethiopia, Kenya and Tanzania. To account for the morphological variability, 10 subspecific taxa (subspecies and varieties) have been described that are separated geographically or ecologically. Due to the high oil and vernolic acid content and its relatively low shattering nature, subsp. galamensis var. ethiopica M.G.Gilbert has been the focus of research aiming at domestication and commercialization.
Growth and development
Seed may show some dormancy for a few months after maturation; thereafter germination takes about 10 days. Plants form a single unbranched stem ending in an inflorescence. Growth is indeterminate. Some plants may reach a height of only 20 cm and form only a single flowerhead, while others become vigorous, more than 2.5 m tall shrubs with many branches and flowerheads. Flowering is induced by short days, but plants have been found in subsp. galamensis var. petitiana (A.Rich.) M.G.Gilbert in southern and northern Ethiopia and Kenya that are only weakly quantitatively sensitive to daylength.
In an experiment with selections of var. ethiopica at different locations in Ethiopia, flowering started 87117 days after sowing, and seeds matured after 161261 days. When growing conditions permit, branching starts after formation of the main inflorescence and occurs only at the higher nodes; these branches may also form flowerheads. As a result ripening of the heads of a plant may be uneven. Shattering of mature fruiting heads occurs in most types, but types with limited shattering have been identified. Vernonia galamensis is self-fertile, but rates of outcrossing of up to 16% have been found.
Vernonia galamensis is adapted to the semi-arid tropics where it is found in dry bushland, but more often in ruderal places and as a weed of cultivation, up to 2000(2500) m altitude. Only subsp. afromontana (R.E.Fr.) M.G.Gilbert var. afromontana occurs in montane forest, often in undisturbed areas. Rainfall may be as low as (250)500 mm for some types, but as high as 1850 mm for other ones. In cultivation, Vernonia galamensis requires a rainy season that provides sufficient moisture to permit the main flowerheads to develop; a longer rainy season that permits secondary flowerheads to develop will result in poor uniformity of maturation and a risk of seed shattering. The plants tolerate substantial shading, which may make cultivation in agroforestry systems possible. A well-drained soil with pH 5.08.5 is preferred. On poorly drained soils, growth of the main stem stops before flowering; branches develop from the base of the plant, but they also wither and die.
Propagation and planting
Vernonia galamensis is propagated by seed. As the seed is small, a firm, level seedbed is required. In experimental plantings in the United States plant spacings of 90100 cm between rows and 1530 cm within the row have given good results. In Ethiopia high yields for var. ethiopica were obtained at 40 cm between and 10 cm within rows. The weight of 1000 seeds is (2.5)3.44.3 g; in var. afromontana larger seeds have been recorded, 1000 seeds weighing 5.4 g. The number of seeds per head averages about 240.
Seedling growth is slow and weeding is important. Pre-sowing herbicides have been applied successfully. Topping of young plants may reduce the risk of lodging and enhance uniform maturation. In a trial in Zimbabwe, plants of var. ethiopica topped at a height of 15 cm led to the development of 1820 main branches per plant, each with 35 flowerheads. At harvesting, plant heights were less, lodging was significantly reduced and seed maturity more uniform. In var. petitiana, which tends to be shorter, the effect of topping was less pronounced. Fertilizer recommendations are not yet available, but in experiments in the United States, N applications of 100 kg/ha have given good results. In Ethiopia 150 kg N/ha caused lodging. Application of K and P gave little response.
Diseases and pests
A leaf blight caused by Alternaria alternata, a root rot caused by a complex of Fusarium solani, Rhizoctonia solani and Sclerotium rolfsii and rust caused by Puccinia sp. have been observed where Vernonia galamensis has been grown for several years. Selections differed markedly in susceptibility. In Ethiopia a moderate incidence of helmet bug (Captosoma sp.) has been observed on maturing flowerheads and on young shoots, leaves and growing points, sometimes resulting in profuse branching of the stem. Harlequin bug (Bagrada sp.) infestation, which causes wilting, may also develop into a serious pest. Cuscuta campestris Yunk. has been found as a parasitic weed on Vernonia galamensis under natural and under field conditions.
Vernonia galamensis matures unevenly and several harvesting rounds are often necessary. Harvesting of heads is done when the involucres surrounding the seeds are dry and spread out to release the fully mature seeds. At this stage seeds are 90% black in colour and firm. In var. ethiopica selections have been found with seed that remains on the plant for about 30 days after maturity. Growers can therefore postpone the harvest of a heterogeneous crop until most seeds are ripe.
In the United States experimental seed yields of up to 2500 kg/ha from the best germplasm have been recorded. The best yields recorded in Ethiopia from local selections are 4000 kg/ha of seed, equivalent to 1625 kg/ha of oil.
Handling after harvest
After the harvest, first the seeds are separated from the heads, then the pappus is removed from the seed. These are laborious and labour intensive operations if carried out manually.
Var. ethiopica is considered most promising as it has a high yield potential, high oil content, high vernolic acid content and good seed retention. Daylength-neutral types were found in var. petitiana in northern and southern Ethiopia and in Kenya. They are being used in breeding programmes in the United States.
Germplasm collections are maintained at the North Central Regional Plant Introduction Station, Ames, Iowa, United States (53 accessions) and at the National Genebank, KARI, Muguga, Kenya (38 accessions). Germplasm collection has covered most of Ethiopia. Nearly 500 accessions were collected from a wide range of habitats from1250 m to 2050 m altitude. They are being maintained and evaluated by the Alemaya University and Ethiopian Institute for Agricultural Research through its research stations in the country. The Ethiopian Institute of Biodiversity Conservation and Research holds a collection of 14 accessions.
In the United States, where daylength-neutral plants are needed, the focus of breeding work is on hybrids of var. ethiopica and var. petitiana to obtain high-yielding, daylength neutral types with good seed retention and non-dormant seed. Several generations of these selections have been produced and are being evaluated. Some breeding work, focussing on the characterization of germplasm, is being conducted in Ethiopia.
Especially for semi-arid tropical areas, Vernonia galamensis remains a promising oil plant, yielding an industrial raw material that can only partially be replaced by chemically prepared products. Its success, however, depends on the economic yields that can be obtained with improved selections and on the further development of industrial applications requiring the specific qualities of vernolic acid.
In general, this crop is suitable for cultivation in semi-arid and arid areas and can serve as a new cash crop, and hence create diversification of agricultural products for the farmers in developing countries of the tropics.
Baye, T., 2002. Genotypic and phenotypic variability in Vernonia galamensis germplasm collected from eastern Ethiopia. Journal of Agricultural Science 139(2): 161168.
Baye, T., 2004. Exploration, genetic diversity and seed quality analyses in Ethiopian populations of Vernonia galamensis. Cuvillier Verlag, Gφttingen, Germany. 170 pp.
Baye, T. & Becker, H.C., 2005. Exploration of Vernonia galamensis in Ethiopia, and variation in fatty acid composition of seed oil. Genetic Resources and Crop Evolution 52(7): 805811.
Baye, T. & Becker, H.C., 2005. Genetic variability and interrelationship of traits in the industrial oil crop Vernonia galamensis. Euphytica 142(1-2): 119129.
Baye, T., Kebede, H. & Belete, K., 2001. Agronomic evaluation of Vernonia galamensis germplasm collected from Eastern Ethiopia. Industrial Crops and Products 14: 179190.
Gilbert, M.G., 1986. Notes on the East African Vernonieae (Compositae), 4. A revision of the Vernonia galamensis complex. Kew Bulletin 41(1): 1935.
Jeffrey, C., 1988. The Vernonieae in East tropical Africa. Notes on Compositae 5. Kew Bulletin 43(2): 195277.
Perdue Jr., R.E., Carlson, K.D. & Gilbert, M.G., 1986. Vernonia galamensis, potential new crop source of epoxy acid. Economic Botany 40(1): 5468.
Shimelis, H.A., Labuschagne, M.T. & Hugo, A., 2006. Variation in oil content and fatty acid composition in selected lines of vernonia (Vernonia galamensis var. ethiopica). South African Journal of Plant and Soil 23(1): 6263.
Trumbo, D.L., Rudelich, J.C. & Mote, B.E., 1999. Application of vernonia oil in coatings. In: Janick, J. (Editor). Perspectives on new crops and uses. ASHS Press, Alexandria VA, United States. pp. 267271.
Baye, T. & Becker, H.C., 2004. Natural outcrossing rate in Vernonia galamensis. Plant Breeding 123(4): 398399.
Baye, T., Becker, H.C. & Witzke-Ehbrecht, S.V., 2005. Vernonia galamensis, natural source of epoxy oil: Variation in fatty acid composition of seed and leaf lipids. Industrial Crops and Products 21: 257261.
Beentje, H.J., 2000. Compositae (part 1). In: Beentje, H.J. (Editor). Flora of Tropical East Africa. A.A. Balkema, Rotterdam, Netherlands. pp. 1313.
Beentje, H., Eriksson, T., Kilian, N., King-Jones, S., Thulin, M., Mesfin Tadesse, Ortiz, S.& Rodrνguez-Oubiρa, J., 2005. Asteraceae (Compositae). In: Thulin, M. (Editor). Flora of Somalia. Volume 3. Angiospermae (cont.). Royal Botanic Gardens, Kew, Richmond, United Kingdom. pp. 465558.
Bhardwaj, H.L., Hamama, A.A., Rangappa, M. & Dierig, D.A., 2000. Vernonia oilseed production in the mid-atlantic region of the United States. Industrial Crops and Products 12: 119124.
Carlson, K.D., Schneider, W.J., Chang, S.P. & Princen, L.H., 1981. Vernonia galamensis seed oil: a new source for epoxy coatings. In: Pryde, E.H., Princen, L.H. & Mukherjee, K.D. (Editors). New sources of fats and oils. AOCS Monograph 9. American Oil Chemists Society, Champaign Illinois, United States. pp. 297318.
Dierig, D.A. & Thompson, A.E., 1993. Vernonia and Lesquerella potential for commercialization. In: Janick, J. & Simon, J.E. (Editors). New Crops. Wiley, New York, United States. pp. 362367.
Metzger, J.O. & Bornscheuer, U., 2006. Lipids as renewable resources: current state of chemical and biotechnological conversion and diversification. Applied Microbiology and Biotechnology 71(1): 1322.
Robinson, H., 1999. Revisions in paleotropical Vernonieae (Asteraceae). Proceedings of the Biological Society of Washington 112: 220246.
Tefera, T. & Baye, T., 2003. Mycoflora associated with new industrial oilseed crop (Vernonia galamensis var. ethiopica) in Ethiopia. Tropical Science 43: 69.
Teynor, T.M., Putnam, D.H., Oplinger, E.S., Oelke, E.A., Kelling, K.A. & Doll, J.D., 1992. Vernonia. Alternative Field Crops Manual. [Internet] University of Wisconsin Extension, Madison, United States. http://www.hort.purdue.edu/ newcrop/afcm/ vernonia.html. Accessed January 2007.
Thompson, A.E., Dierig, D.A., Johnson, E.R., Dahlquist, G.H. & Kleiman, R., 1994. Germplasm development of Vernonia galamensis as a new industrial oilseed crop. Industrial Crops and Products 3: 185200.
Thompson, A.E., Dierig, D.A. & Kleiman, R., 1994. Characterization of Vernonia galamensis germplasm for seed oil content, fatty acid composition, seed weight, and chromosome number. Industrial Crops and Products 2: 299305.
Sources of illustration
Gilbert, M.G., 1986. Notes on the East African Vernonieae (Compositae), 4. A revision of the Vernonia galamensis complex. Kew Bulletin 41(1): 1935.
Correct citation of this article:
Baye, Tesfaye M. & Oyen, L.P.A., 2007. Vernonia galamensis (Cass.) Less. In: van der Vossen, H.A.M. & Mkamilo, G.S. (Editors). PROTA 14: Vegetable oils/Olιagineux. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, lower part of stem and roots; 2, upper part of flowering stem; 3, fruit.
Redrawn and adapted by Achmad Satiri Nurhaman