Prota 3: Dyes and tannins/Colorants et tanins
Icon. 1: 56, t. 79 (1791).
2n = 24
Bidens sulphurea (Cav.) Sch.Bip. (1856).
Orange cosmos, yellow cosmos, sulphur cosmos (En). Cosmos soufré (Fr). Cosmos amarelo (Po).
Origin and geographic distribution
Cosmos sulphureus originates from Central America (Mexico) and northern South America, where it is still found in the wild. It has been introduced as an ornamental in many countries all over the world, in tropical Africa e.g. in Senegal, Cameroon, Sudan, Tanzania, Malawi, Zambia, Zimbabwe, Mozambique, Réunion and Mauritius. Sometimes it has escaped from cultivation and behaves like a weed, e.g. in Tanzania, Malawi, Zimbabwe, the United States and Canada.
The flower heads of Cosmos sulphureus and other Cosmos, Bidens and Coreopsis species have been major sources of yellow to orange dyes among the precolumbian civilizations of Central and South America. In southern Africa, they were adopted as a popular yellow dye by European settlers for domestic textile production and are still used by dyers using natural dyes as a hobby or for textile crafts, to dye wool bright yellow or orange. The flowers should first be boiled for about one hour before adding the mordanted wool to the cooled dye-bath and resuming boiling. Pre-mordanting the fibres with different metallic salts gives various shades of lemon yellow to burnt orange. As a top-dye after a first red dyewood bath (e.g. of Baphia nitida Lodd.), it helps give a scarlet bloom to wool while on indigo-dyed wool, it produces greenish-brown shades. Cosmos sulphureus is commonly cultivated as an ornamental.
The flower heads of most Cosmos, Bidens, and Coreopsis species contain flavonoid dyes of the chalcone and aurone groups. The specific flavonoids in Cosmos have not been fully elucidated, though the following have been found: luteolin, a group of flavonols having quercetin as their aglycone, and a group of chalcone glycosides. These are all good yellow colorants. The traditional medicinal applications in China of Cosmos and Bidens species have been confirmed by the fact that Cosmos and Bidens extracts are shown to inhibit bacteria, fungi, and viruses and to have potent anti-inflammatory effects in laboratory animal experiments with induced gastric ulcer, liver inflammation, or arthritis-type swelling.
Annual herb up to 1.2(–2) m tall, with 4-angled, branched, pubescent to glabrescent stem. Leaves opposite, sessile or with clasping petiole up to 2 cm long; blade ovate in outline, up to 7 cm × 5 cm, very deeply dissected with ultimate segments narrowly oblong, c. 2.5 mm wide, apiculate, glabrous. Inflorescence a head c. 1.5 cm in diameter, solitary and terminal on stem and branches; peduncle up to 22 cm long (often much less); outer involucral bracts narrowly ovate, c. 12 mm long, acuminate, inner bracts with membranous margin. Ray flowers c. 10, corolla oblong-obovate, up to 3 cm long, apex 3-toothed, deep orange; disk flowers with narrowly funnel-shaped corolla, 5-lobed, c. 7 mm long, orange-yellow, subtended by scales c. 9 mm long. Fruit an achene c. 2 cm long, blackish, with a scabrid beak c. 7 mm long; pappus of 2 horizontally spreading awns c. 5 mm long.
Cosmos comprises about 25 species from tropical America; it belongs to the tribe Heliantheae and is related to the much larger genera Bidens and Coreopsis. Cosmos sulphureus as an ornamental comprises several cultivars.
Where Cosmos sulphureus has been found in the wild in Africa, it is a common roadside weed which does not spread into undisturbed localities. In southern Africa it flowers and fruits in March–May.
Cosmos sulphureus is propagated by seed. The flower heads of about two dozen plants are sufficient to dye 0.5 kg of wool or silk. They should be harvested when they open. They are soaked in water and the mixture is cooked until the flower heads become pale. The dye bath is yellowish in an acid solution (e.g. with vinegar) and reddish in a basic solution (e.g. with ammonia or washing soda). Alum and tartaric acid are often added as a mordant. The textile is simmered in the dye bath until the desired depth of colour is achieved, usually after about one hour.
Genetic resources and breeding
Cosmos sulphureus is widespread in Central America and elsewhere it may behave as a weed. It does not seem to be in danger of genetic erosion. Breeding efforts are directed towards development of large-flowered ornamentals.
As a source of orange to yellow dyes, Cosmos sulphureus will remain only locally of importance in southern Africa and in Western countries.
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Correct citation of this article:
Jansen, P.C.M., 2005. Cosmos sulphureus Cav. In: Jansen, P.C.M. & Cardon, D. (Editors). PROTA 3: Dyes and tannins/Colorants et tanins. [CD-Rom]. PROTA, Wageningen, Netherlands.