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Pauridiantha rubens (Benth.) Bremek.

Bot. Jahrb. 71: 215 (1940).
Urophyllum rubens Benth. (1849).
Origin and geographic distribution
Pauridiantha rubens is found in Cameroon, Central African Republic, Equatorial Guinea, Gabon and DR Congo.
Young leaves of Pauridiantha rubens yield a red dye, which is used in Bioko (Equatorial Guinea) and for which the plant is cultivated there. How the dye is used is not reported.
The nature of the red dye present in the leaves of Pauridiantha rubens has not been studied. Several alkaloids have been identified in related species: harman, pauridianthin and pauridianthinin in the root bark of Pauridiantha callicarpoides (Hiern) Bremek., and pauridianthin and pauridianthinol in Pauridiantha lyalii Bremek. The dye potential of Pauridiantha rubens is optimized by the mordanting effect of the aluminium present in the leaves. Aluminium accumulation in leaves seems to be a chemotaxonomic characteristic of the Pauridiantha genus.
Shrub or small tree up to 7 m tall, almost glabrous, with stem up to 15 cm in diameter. Leaves opposite, simple and entire; stipules up to 25 mm × 14 mm, normally persistent but falling near inflorescences; petiole up to 3.5 cm long; blade elliptical, 12–32 cm × 5–15 cm, base acute, apex acuminate, midrib very prominent below, young leaves brownish above, red below. Inflorescence an axillary panicle up to 4 cm long, solitary or in pairs; peduncle 1–1.5 cm long. Flowers bisexual, regular, 5-merous; pedicel up to 4 mm long; calyx cupular, truncate at apex or with small teeth; corolla white-green to green, tubular with triangular lobes up to 2 mm long; stamens short; disk c. 2 mm in diameter; ovary inferior, 2-celled, style c. 3 mm long, ending in 2 stigmatic lobes. Fruit a flattened globose berry up to 5 mm × 8 mm, many-seeded. Seeds c. 1 mm long.
Pauridiantha comprises about 25 species, all African (1 in Madagascar).
Pauridiantha rubens is found at forest edges and edges of clearings, from sea-level up to 500 m altitude.
Genetic resources and breeding
Pauridiantha rubens is widespread and does not seem to be in danger of genetic erosion.
The use of the young leaves of Pauridiantha rubens as source of a red dye may remain only locally of some importance, but in the present conjuncture of renewed interest in natural dyes as renewable sources of non-polluting colorants, the combination in the same plant of a red dye and a mordant because of the presence of aluminium makes Pauridiantha rubens interesting, especially since it has been or still is cultivated. Methods of cultivation, chemical composition and traditional dye processes therefore deserve further investigation.
Major references
• Bremekamp, C.E.B., 1941. Ist die Gattung Urophyllum Wall. in Africa vertreten? Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 71: 200–227.
• Burkill, H.M., 1997. The useful plants of West Tropical Africa. 2nd Edition. Volume 4, Families M–R. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 969 pp.
• Hallé, N., 1966. Rubiacées (1re partie). Flore du Gabon. Volume 12. Muséum National d’Histoire Naturelle, Paris, France. 278 pp.
• Jansen, S., Dessein, S., Piesschaert, F., Robbrecht, E. & Smets, E., 2000. Aluminium accumulation in leaves of Rubiaceae: systematic and phylogenetic implications. Annals of Botany 85: 91–101.
Other references
• Hepper, F.N. & Keay, R.W.J., 1963. Rubiaceae. In: Hepper, F.N. (Editor). Flora of West Tropical Africa. Volume 2. 2nd Edition. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. pp. 104–223.
• Hiern, W.P., 1877. Rubiaceae. In: Oliver, D. (Editor). Flora of tropical Africa. Volume 3. L. Reeve & Co, Ashford, United Kingdom. pp. 33–247.
• Khan, S.I., Abourashed, E.A., Khan, I.A. & Walker, L.A., 2004. Transport of harman alkaloids across caco-2 cell monolayers. Chemical and Pharmaceutical Bulletin 52(4): 394–397.
• Levesque, J., Jacquesy, R. & Foucher, J.P., 1982. Alcoyl-gluco-alcaloides: nouveaux composés isolés de Pauridiantha lyalii Brem. (Rubiacées). Tetrahedron 38(10): 1417–1424.
• Pousset, J.-L., Bouquet, A., Cavé, A. & Paris, R.-R., 1971. Structure de deux nouveaux alcaloïdes isolés de Pauridiantha callicarpoides Brem. (Rubiacées). Compte-rendus de l’Académie des Sciences, Paris 272: 665–667.
P.C.M. Jansen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

P.C.M. Jansen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
D. Cardon
CNRS, CIHAM-UMR 5648, 18, quai Claude-Bernard, 69365 Lyon, Cedex 07, France
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Jansen, P.C.M., 2005. Pauridiantha rubens (Benth.) Bremek. In: Jansen, P.C.M. & Cardon, D. (Editors). PROTA 3: Dyes and tannins/Colorants et tanins. [CD-Rom]. PROTA, Wageningen, Netherlands.