Prota 3: Dyes and tannins/Colorants et tanins
Prodr. 10: 94 (1846).
Arabian primrose (En). Sang de l’homme (Fr).
Origin and geographic distribution
Arnebia hispidissima occurs from northern tropical Africa, through Egypt, to northern India. In tropical Africa it has been recorded from northern Nigeria, Cameroon, Chad and Sudan.
The roots of Arnebia hispidissima are collected from the wild. They are dark purple and provide a dye giving purplish-red to purple colours. In Nigeria the Hausa call the dye ‘jinin mutum’ (blood of man) and it is used to colour clothes and the body. In India the dye is included in the group of Boraginaceae species the roots of which are sold under the commercial name ‘ratanjot’, used to colour food and to dye silk. In Sudan the plant is grazed by sheep. In Indian traditional medicine root extracts are used to treat ulcers, boils, cuts, throat complaints, heart problems, headache and fever, and extracts of the whole plant as a stimulant, tonic, diuretic and expectorant.
The red pigment in the roots of Arnebia hispidissima is composed of a group of naphthoquinonic dyes including shikonin (and esters), its optical isomer alkannin (and derivatives) and their common racemic form shikalkin, as well as arnebifuranone which is another type of compound. The same naphthoquinonic colorants are also present in the roots of several other Boraginaceae species traditionally used as body paint or textile dyes in other parts of the world (e.g. Alkanna tinctoria (L.) Tausch. in Europe and the Mediterranean region, Lithospermum erythrorhizon Siebold & Zucc. in China and Japan, Lithospermum caroliniense (Walter ex J.F.Gmel.) Macmil. in North America). They are poorly soluble in water but more easily so in alcohol and fats, which explains their uses as colorants in cosmetics. In India, medicinal active principles isolated from the aerial parts include arnebins and the triterpenoids betulin, β-amyrin and lupeol. All compounds (of both roots and aerial parts) showed antimicrobial activity, more powerfully against bacteria than against fungi.
Annual herb up to 40 cm tall, erect or ascending, much branched from the base, with strong red roots, densely covered with white bristles. Leaves alternate, simple, without stipules, sessile; blade linear-lanceolate, 1.5–8 cm × 0.2–1 cm, apex acute to obtuse, margin entire. Inflorescence spike-like, consisting of terminal, short and dense scorpioid cymes, simple or forked; bracts leaf-like. Flowers sessile, bisexual, regular, 5-merous; calyx deeply divided, lobes 5–8 mm long, unequal, hardly accrescent in fruit; corolla tubular, 8–16 mm long, yellow, tube hairy inside, lobes small; stamens inserted at about the middle of the corolla tube, filaments c. 0.5 mm long, anthers 1.5 mm; ovary superior, 4-lobed, style c. 1 cm long, 2-lobed, each lobe ending in a reniform stigma. Fruit consisting of 4 pyramidal nutlets up to 2 mm long, ventrally keeled, granulose to smooth, grey to yellow-brown.
Arnebia comprises about 25 species, and is confined to tropical Africa, the Mediterranean region and the Himalayas. In tropical Africa 3 species occur. In traditional medicine in China, roots of other Arnebia species have similar uses to those of Arnebia hispidissima in India.
Arnebia hispidissima occurs on dry, stony or sandy soils, often in desert plains and disturbed localities along fields.
Genetic resources and breeding
Arnebia hispidissima is widespread and not in danger of genetic erosion.
The dyeing properties of Arnebia hispidissima, especially the liposolubility of the root dyes make it an interesting source of colorants for the food and cosmetic industries. Collecting of the roots in their wild environment could quickly lead to the rarefaction and even extinction of the plant, should material in large quantities be needed. Consequently, the possibilities for cultivation should be investigated. The medicinal properties of Arnebia hispidissima most probably will remain only locally of importance, although they deserve more research.
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Correct citation of this article:
Jansen, P.C.M., 2005. Arnebia hispidissima (Sieber ex Lehm.) DC. In: Jansen, P.C.M. & Cardon, D. (Editors). PROTA 3: Dyes and tannins/Colorants et tanins. [CD-Rom]. PROTA, Wageningen, Netherlands.