Prota 3: Dyes and tannins/Colorants et tanins
Fl. ind. ed. 1832, 2: 349 (1832).
Caesalpiniaceae (Leguminosae - Caesalpinioideae)
2n = 14, 16, 28
Cassia auriculata L. (1753).
Avaram, tanner’s cassia, tarwar (En). Avaram (Fr). Avúl (Po).
Origin and geographic distribution
Senna auriculata is a native of India, Myanmar and Sri Lanka and has been successfully introduced into several African countries. It has been suggested that it is indigenous in Tanzania, but an early introduction and naturalization seem more likely. It is cultivated in India and Sri Lanka, and occasionally elsewhere.
Senna auriculata is a multipurpose plant. The bark can be used for tanning heavy hides and goat and sheep skins, giving a buffcoloured leather of good quality, which tends to darken to black-red on exposure to light. To prevent this darkening the leather is often finished by a tannage using myrobalans from Terminalia chebula Retz. In southern India the flowers are used as a fast yellow dye for leather. In Gujarat the flower buds are used in the galling process prior to dyeing cotton cloth and chintzes red, pink or purple with madder roots (Rubia cordifolia L.). Boiled seeds are an important ingredient in indigo vats, where specific bacterial fermentation ensures the reduction of insoluble indigo into the soluble leuco-indigo, allowing textile fibres to be impregnated by the dye solution. The seeds of Senna auriculata serve as a source of sugars to keep the fermentation process going.
Branches are used as chewing sticks and toothbrushes. The bark fibre can be made into rope, and a fermented mixture of pounded bark and dissolved molasses serves as an alcoholic beverage in some parts of India. Senna auriculata does not reach a volume adequate for timber, but sometimes handles of small tools are made from the wood. It is used for revegetating erodible soils and as a green manure, and has also proved very effective in reclaiming sodic soils which have been dressed with gypsum. The leaves are sometimes used to make tea, dried flowers serve as a coffee substitute, and in times of food scarcity the young tender pods, young leaves and flowers are eaten as a vegetable. The quantity eaten is critical since Senna auriculata is considered not well suited as fodder for goats and cattle because of the poisonous substances in the plant. The stem bark is used in India to stupefy fish. Uses in traditional medicine are numerous. The roots and bark are astringent and are used for gargles, as an alterative, and to cure skin diseases, eye troubles and rheumatism. A decoction of the flowers and the seeds is recommended for diabetes, seeds are used to cure eye diseases, gonorrhoea and gout. In Tanzania the plant is used to treat impotence, which may be related to diabetes. Leaves and fruits serve as an anthelmintic and diuretic. Sometimes Senna auriculata is cultivated as an ornamental. A most curious use of Senna auriculata is reported from India. It is believed that branches were formerly used in the fabrication of wootz Damascus steel. They were added to the crucible and heated with the ore to obtain the chemical composition that gave the steel its beautiful patterning.
Production and international trade
Senna auriculata was a major source of tannin in India, the most important areas of production being Madras, Hyderabad and Mysore. In the past, annual production of dried bark in India reached 50,000 t. For local use, dried bark is marketed in bags of 100–120 kg. Syntans and imported barks, especially of black wattle (Acacia mearnsii De Wild.) from southern Africa, have largely replaced avaram bark. Outside India, Senna auriculata has never been cultivated on a large scale.
The bark of Senna auriculata plants over three years old contains 15–24% of tannin on a dry weight basis. The tannin content increases with age, but the increase slows down after the third year. The tannin penetrates the hide quickly. In the dyeing applications, the tannins present in the plant act as vegetable mordants in combination with colorants of other chemical groups, such as anthraquinone glucosides, detected in the leaves.
Saponin and the cardiac glucoside sennapicrin are reported from the roots. The bark, flowers, and seeds contain pyrrolizidine alkaloids, suspected of hepatotoxic properties. However, in experiments with rats, leaf extracts of Senna auriculata have been shown to alleviate the effects of liver injury caused by alcohol. Extracts of dried flowers showed significant antihyperglycaemic effect in rats, comparable to the therapeutic drug acarbose. This supports the traditional use as a treatment for diabetes.
Shrub or small tree up to 7 m tall, with trunk up to 20 cm in diameter; bark thin, brown, lenticellate. Leaves alternate, paripinnately compound; stipules large and leafy, broadly reniform, 7–22 mm wide, persistent; petiole 10–14 cm long; rachis provided with a gland between each pair of leaflets; leaflets 6–13 pairs, oblongelliptical to obovateelliptical, 10–35 mm × 5–12 mm, rounded and mucronate at apex, glabrous to pubescent. Inflorescence an axillary raceme, 2–8flowered. Flowers bisexual, zygomorphic, 5-merous; sepals rounded at apex; petals free, unequal, 1.5–3 cm long, yellow; stamens 10, the 3 lower ones largest and fertile, others usually sterile; ovary superior, falcate, c. 1.5 cm long, stalked, style c. 1 cm long. Fruit a flattened cylindrical pod 5–18 cm × 1–2 cm, transversely undulate between the 10–20 seeds, indehiscent. Seeds compressed ovoid-cylindrical, 7–9 mm × 4–5 mm, with a distinct areole on each face.
Other botanical information
Until the early 1980s, Cassia was considered to be a very large genus of over 500 species, but then it was split into 3 genera: Cassia s.s. with about 30 species, Senna with 270 species and Chamaecrista with 250 species.
Growth and development
Plants reach about 3 m height with 3.5 cm stem diameter in 2 years, in 4 years about 5 m height and 7 cm stem diameter. Flowering and fruiting is almost throughout the year, but in India there are usually two main flowering periods, one in the early monsoon and another in the late monsoon.
Under natural or naturalized conditions, Senna auriculata is found in woodland and wooded grassland up to 600 m altitude. It usually grows wild in dry regions with a minimum annual precipitation of 400 mm, but it also tolerates wet climates with an annual precipitation of up to 4300 mm. The mean annual temperature can vary from 16°C to 27°C. Senna auriculata needs full sun. It tolerates many soil types, including saline soils, but prefers fairly rich, welldrained soils.
Thinning is necessary one year after sowing. Weeding and cultivation stimulate growth but are not absolutely necessary. Limed soil is reported to increase the amount of tannin. Coppiced plants regrow well.
Propagation and planting
Senna auriculata can be propagated by seed and stem cuttings. For quick germination seeds are scarified and held in running water. The seedlings are fairly resistant to desiccation. Stem cuttings are planted 5–12.5 cm apart in rows.
Starting the third year after establishment, the twig bark of Senna auriculata can be stripped and used. Twigs that have not developed a corky bark are best. Coppiced plants can be harvested annually.
The yield of green bark of Senna auriculata averages 1500 kg per ha in a 4- year-old plantation of about 9000 plants/ha.
Handling after harvest
The bark is sun dried in small pieces and stored or marketed. Unstripped twigs can be directly used by the tanners to make a tanning extract which is as effective as when made from dried stripped bark. To prepare a yellow dye, flowers (about twice the weight of the textile to be dyed) are boiled in water. Then the cloth, previously mordanted with alum, is immersed into the bath, which is kept boiling until the desired shade is obtained. In Andhra Pradesh (India), 2.5 kg of broken and cooked Senna auriculata seeds are added to a vat of indigo of approximately 227 l with 750 g of indigo.
Senna auriculata is widespread and does not seem to be in danger of genetic erosion. The status of the plants found in natural habitats in Tanzania needs further clarification.
Senna auriculata is easy to grow and has numerous uses. The good tanning properties of the bark, the possibility of using the flowers and leaves as renewable dye sources that can be collected without damaging the tree, and its medicinal properties make it an interesting plant for planting in the drier parts of Africa.
• Abesundara, K.J., Matsui, T. & Matsumoto, K., 2004. α-Glucosidase inhibitory activity of some Sri Lanka plant extracts, one of which, Cassia auriculata, exerts a strong antihyperglycemic effect in rats comparable to the therapeutic drug acarbose. Journal of Agricultural and Food Chemistry 52(9): 2541–2545.
• Brenan, J.P.M., 1967. Leguminosae, subfamily Caesalpinioideae. In: Milne-Redhead, E. & Polhill, R.M. (Editors). Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 230 pp.
• Burkill, H.M., 1995. The useful plants of West Tropical Africa. 2nd Edition. Volume 3, Families J–L. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 857 pp.
• CSIR, 1950. The wealth of India. A dictionary of Indian raw materials and industrial products. Raw materials. Volume 2: C. Council of Scientific and Industrial Research, New Delhi, India. 427 pp.
• Duke, J.A., 1981. Handbook of legumes of world economic importance. Plenum Press, New York, United States, and London, United Kingdom. 345 pp.
• Mohanty, B.C., Chandramouli, K.V. & Naik, H.D., 1987. Natural dyeing processes of India. Calico Museum of Textiles, Sarabbiai Foundation, Ahmedabad, India. 284 pp.
• Moshi, M.J. & Mbwambo, Z.H., 2002. Experience of Tanzanian traditional healers in the management of non-insulin dependent diabetes mellitus. Pharmaceutical Biology 40(7): 552–560.
• de Luynes, H., 1844. Mémoire sur la fabrication de l’acier fondu et damassé. [Internet] Paris. http://acier.damas.free.fr/f_damas/f_quest/f_wsteel/luynes.htm. Accessed October 2004.
• Greenway, P.J., 1941. Dyeing and tanning plants in East Africa. Bulletin of the Imperial Institute 39: 222–245.
• Kumar, R.S., Manickam, P., Periyasamy, V. & Namasivayam, N., 2003. Activity of Cassia auriculata leaf extract in rats with alcoholic liver injury. Journal of Nutritional Biochemistry 14(8): 452–458.
• Purseglove, J.W., 1968. Tropical Crops. Dicotyledons. Longman, London, United Kingdom. 719 pp.
• Watt, J.M. & Breyer-Brandwijk, M.G., 1962. The medicinal and poisonous plants of southern and eastern Africa. 2nd Edition. E. and S. Livingstone, London, United Kingdom. 1457 pp.
Sources of illustration
• Maman Rahmansyah, 1991. Cassia auriculata L. In: Lemmens, R.H.M.J. & Wulijarni-Soetjipto, N. (Editors). Plant Resources of South-East Asia No 3. Dye and tannin producing plants. Pudoc, Wageningen, Netherlands. pp. 62–63.
Correct citation of this article:
Jansen, P.C.M., 2005. Senna auriculata (L.) Roxb. In: Jansen, P.C.M. & Cardon, D. (Editors). PROTA 3: Dyes and tannins/Colorants et tanins. [CD-Rom]. PROTA, Wageningen, Netherlands.
planted and naturalized
1, flowering branch; 2, fruit
detail of flowering plant