Prota 11(1): Medicinal plants/Plantes médicinales 1
Encycl. 2: 270 (1786).
2n = 14, 16
Plumbago capensis Thunb. (1794).
Blue plumbago, Cape leadwort, Cape plumbago, skyflower (En). Dentelaire du Cap (Fr). Plumbago azul (Po).
Origin and geographic distribution
Plumbago auriculata is native to South Africa and introduced as an ornamental into most tropical and subtropical countries.
In southern Africa a decoction of the aerial parts or roots of Plumbago auriculata is taken to treat blackwater fever. A root infusion is taken as an emetic. Root powder is put on warts to make them disappear and is also used as snuff to relieve headache. The powdered, roasted root is rubbed into scarifications over fractures to promote healing, and is rubbed on the body to cure stitch. These treatments are not without danger if large areas are rubbed in, as death by irritation has been recorded. The root extract also acts as a styptic in scrofula.
Plumbago auriculata is grown in gardens throughout the tropics as an ornamental and as a hedge or live fence; in temperate regions it is grown as a pot plant or greenhouse plant. Several cultivars with flowers in different shades of blue exist, as well as a white cultivar. In East Africa the flowers and leaves of Plumbago auriculata are used as a dye for textiles: beige, lemon, yellow (if combined with alum) or gold (if combined with chrome). The sap of the roots is grey-blue, and is used for tattoos. Poultry and sheep readily eat the leaves, but poisoning has been recorded.
Production and international trade
Plumbago auriculata is produced commercially and traded as an ornamental throughout the world.
All parts of Plumbago auriculata contain the naphthoquinone plumbagin ( 2-methyl juglone), which blisters the skin. Plumbagin possesses a variety of pharmacological activities, i.e. antimicrobial, anticancer, cardiotonic and antifertility actions. It has insecticidal properties as an antifeedant and as a moulting inhibitor. Plumbagin is also a yellow pigment, occurring in a colourless combined form in the plant and is liberated by acid treatment. Plumbago auriculata contains an antifungal protein that inhibits spore germination in Macrophomina phaseolina.
Perennial herb or small shrub up to 2(–3) m tall; stems erect, trailing or climbing, diffusely branched. Leaves alternate, simple and entire; stipules absent; petiole short with large, amplexicaul auricles at base; blade obovate, elliptical, oblanceolate or spatulate, 2.5–9 cm × 2–6 cm, base long attenuate, apex acute or obtuse, mucronate, pale yellowish-green. Inflorescence a compact terminal spike or raceme, many-flowered, up to 10(–15) cm long; bracts lanceolate, small; peduncle 1–6 cm long, densely hairy. Flowers bisexual, regular, 5-merous; pedicel 0–1 mm long; calyx tubular, 10–12 mm long, 5-ribbed, with sparse short hairs and stalked glands on the upper part; corolla tube cylindrical, 2–3(–4) cm long, lobes broadly obovate, 10–15 mm long, spreading, usually pale blue, sometimes darker blue or white; stamens free, exserted; ovary superior, 1-celled, style filiform, stigma lobes elongated. Fruit an oblong, membranous capsule up to 8 mm long, tapering to the apex, enclosed in the persistent calyx, dehiscent, 1-seeded. Seed oblong, c. 7 mm long, slightly flattened, dark brown or black.
Plumbago comprises about 25 species and occurs almost throughout the world. In tropical Africa about 10 species can be found. Plumbago auriculata flowers all year round, except if the temperature drops below 10°C. The flowers attract large numbers of butterflies.
Plumbago auriculata prefers fertile, well-drained, slightly acidic, sandy soils in sunny localities and is drought resistant once established. It grows best in regions with a pronounced dry season. It can withstand some frost; even if killed to the ground, it usually recovers quickly. Plumbago auriculata is salt tolerant.
Plumbago auriculata is propagated by seed, division of older plants, rooted suckers or semi-ripe cuttings. The seeds are sown in seedling trays in a light soil, after which the soil needs to remain moist. The plants are often pruned to form low hedges or borders and are sometimes trained as climbers on arches. Periodic heavy pruning and bright sunlight induce prolific flowering. In temperate regions, Plumbago auriculata can be grown in containers, and kept in a nursery during winter.
Genetic resources and breeding
Plumbago auriculata is widely cultivated and there is no risk of genetic erosion. Several ornamental cultivars are available, e.g. ‘Imperial Blue’, ‘Royal Cape’ with deep blue flowers, ‘Blue Dark’ with dark blue flowers and ‘Alba’ with white flowers.
Plumbagin possesses various interesting pharmacological activities, but because of its toxicity the use of Plumbago auriculata in traditional medicine is not without risk. Decoctions of plant parts from Plumbago auriculata in local medicine should therefore be taken with caution.
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Correct citation of this article:
de Ruijter, A., 2006. Plumbago auriculata Lam. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
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