Prota 11(1): Medicinal plants/Plantes médicinales 1
Gard. dict. ed. 8: Senna No 1 (1768).
Caesalpiniaceae (Leguminosae - Caesalpinioideae)
2n = 28, 56
Cassia senna L. (1753), Cassia angustifolia Vahl (1790), Cassia acutifolia Delile (1813).
Senna, Aden senna, Alexandrian senna, Indian senna, narrow-leaved senna, Nubian senna, Khartoum senna, true senna (En). Séné, séné vrai, séné d’Egypte, cassier, séné grandes feuilles (Fr). Sene, cássia, senna, cene (Po). Msahala (Sw).
Origin and geographic distribution
Senna alexandrina occurs naturally from Mali eastwards to Somalia and Kenya. It is also native in Asia from the Arabian Peninsula to India and Sri Lanka. In Mozambique it was probably introduced a long time ago and it has also been introduced in a number of Central Asian and Mediterranean countries, the Caribbean and Mexico. Commercial cultivation takes place in India, Sudan, Egypt, Pakistan, China and Korea.
Leaves and pods of Senna alexandrina have been used as a laxative and purgative since ancient times and the trade dates back to at least the 9th century A.D. In the Western world Senna alexandrina was included in most pharmacopoeias under the names ‘Senna folium’ and ‘Senna fructus’. The plant is also important in traditional Indian and Chinese medicine. In Sudan, Ethiopia, Somalia and Kenya both leaves and pods are used as a purgative. In Sudan a decoction of the pods is drunk to get rid of intestinal worms and to cure difficulties in breathing. The infusion of the pods is recommended as a purgative for pregnant women and also to suppress fever. An infusion of the leaves is drunk to overcome flatulence and convulsions and to stop nosebleeds.
In Ethiopia the wood is used to make farm tools. The shrubs are grazed by camels and goats in Somalia. However, in Sudan Senna alexandrina tends to dominate vegetation in heavily grazed areas, which indicates that it is not readily eaten by livestock. In Ethiopia the species is recommended for soil conservation.
Production and international trade
India is the world’s largest producer and exporter of leaves and pods of Senna alexandrina. It exported 5000–7000 t of leaves and pods annually around 1990, mainly to Germany, the United Sates, Japan, the Netherlands, France, Switzerland and the United Kingdom. In 2003 an amount of 9700 t of leaves alone was exported. Annual figures for exports from Sudan vary from 700–7740 t of leaves and pods. In 1992 the price at the port of import was US$ 1600 per t for pods from India and US$ 1200 per t for pods from Sudan. The price of leaves was about 50% lower than that of pods.
The active constituents of the leaves and the wall of the pods are essentially the same and consist of 2–5% anthraquinone derivatives and related dianthrone glycosides on dry weight basis. The dried drug contains mainly sennosides A and B, together with small quantities of related compounds. The sennosides are little resorbed in the small intestine but once in the colon, they are hydrolyzed by the bacterial flora and the anthraquinones formed are reduced to form the active anthrones, which are responsible for the laxative activity as they stimulate peristalsis. Pharmaceutical grade leaves must contain 5.5–8.0% sennoside B, whereas pods must contain at least 2.2% (‘Tinnevelly senna’) to 3.4% (‘Alexandrian senna’) sennoside B.
Much medical research has been published, especially on the use of Senna alexandrina as a laxative and on its possible health risks. No carcinogenic effects of prolonged use have been found in tests with rats, but even so it should only be used for occasional constipation, as prolonged use can lead to chronic ulcerative colitis. Use of the drug is contraindicated in case of intestinal obstruction and acute intestinal inflammation. Use for children under 12 years of age and pregnant or lactating women must be discouraged. The use of preparations for weight reduction is dangerous.
Ethanol extracts of leaves of Senna alexandrina show inhibitory activity against Bacillus cereus, Staphylococcus aureus and Staphylococcus epidermidis, but not against gram-negative bacteria.
Adulterations and substitutes
As a purgative Senna alexandrina is often substituted for other Senna species and by Cassia and Aloe species. Adulteration of commercial products used to be common and profitable, but importing countries nowadays have tight rules and controls. Up to 90% adulteration with Senna auriculata (L.) Roxb. (‘avaram’) has been recorded, and Senna italica Mill. (‘Senegal senna’) was also commonly used. In many African countries commercial preparations are imported.
Deciduous shrub up to 3 m tall. Leaves arranged spirally, paripinnately compound with 4–10 pairs of leaflets; stipules linear to narrowly triangular, 1.5–5 cm long, acute, persistent; petiole 1–8 cm long; leaflets lanceolate or narrowly elliptical to elliptical, 2–6.5 cm × 0.5–1.5 cm, base cuneate, unequal, apex rounded to obtuse, mucronate, shortly hairy on both sides. Inflorescence an erect, axillary raceme 5–30 cm long, 20–30-flowered; bracts elliptical to obovate, c. 1 cm long. Flowers bisexual, zygomorphic, 5-merous; sepals c. 1 cm long, rounded at apex; petals unequal, (oblong-)obovate, 1.5–3 cm long, yellow or orange-yellow; stamens 10, the 2 lower ones largest, 5 medium-sized, 3 short and sterile; ovary superior, woolly, recurved, style short. Fruit a flattened, slightly curved to almost straight, oblong pod 4–7 cm × 1.5–2.5 cm, transversely partitioned, tardily dehiscent by 2 valves, 9–16-seeded. Seeds oblong or oblong-ovate, compressed, 8–9 mm × 4–5 mm, with a small areole on each face.
Other botanical information
Until the early 1980s, Cassia was considered a very large genus of about 550 species, but was then split into 3 genera: Cassia s.s. with about 30 species, Chamaecrista with about 250 species and Senna with about 270 species. Senna is very similar to Cassia, but is distinguished from it by the possession of 3 adaxial stamens which are short and straight, and the pedicels which have no bracteoles.
Two varieties are distinguished in Senna alexandrina: var. obtusata (Brenan) Lock, restricted to Eritrea, Ethiopia, Somalia and northern Kenya, and var. alexandrina, which is the more widespread variety. The distinction made in trade between Indian or Tinnevelly senna from India and Nubian or Alexandrian senna from Sudan has no taxonomic basis.
Several other East African Senna species have medicinal uses similar to those of Senna alexandrina, but are of local importance only. In Somalia many share the same vernacular name ‘jalelo’. Senna holosericea (Fresen.) Greuter occurs in Sudan, Eritrea, Ethiopia, Djibouti and Somalia and extends eastwards to India. The pods and leaves are used in Ethiopia as a laxative. The pods and leaves of Senna hookeriana Batka (synonyms: Cassia adenensis Benth., Cassia somalensis Serrato) from Somalia and Socotra are used as a laxative in Somalia. Senna baccarinii (Chiov.) Lock of southern and eastern Ethiopia, Somalia and northern Kenya is similarly used as the previous species, and twigs are used as toothbrush. It is also grown as an ornamental. Senna longiracemosa (Vatke) Lock is native to Ethiopia, Somalia, Kenya, Uganda and Tanzania and the roots are used by Somali people and the Samburu people of Kenya as a remedy for malaria. Roots are pounded and boiled and the filtrate is drunk with milk.
Growth and development
Senna alexandrina can be found flowering and fruiting throughout the year. It does not form root nodules and does not fix nitrogen.
In tropical Africa Senna alexandrina occurs in semi-desert scrub and grassland particularly in valley bottoms, flood plains and on river banks, and is often associated with Acacia spp. It occurs from sea-level up to 1300 m altitude. Germination is hampered by salinity but older plants are salt-tolerant. Senna alexandrina does not tolerate continuous waterlogging or heavy irrigation.
Propagation and planting
Senna alexandrina is usually established by broadcasting treated seed at rates of 15–25 kg/ha. Untreated seed has a poor germination rate. Treatment of the seed with sulphuric acid is more effective in breaking dormancy than methanol, boiling water, or incision of the testa. The weight of 1000 seeds is about 30 g.
In India Senna alexandrina is mostly grown as a rainfed crop or as a second crop after rice. In rice fields it germinates on residual moisture and can be irrigated. Before the canopy closes one or two weedings are necessary. The first flower stalks that appear are cut, which induces branching and increases the sennoside content of the leaves. Senna alexandrina is mostly grown as an annual crop, but can be left standing to produce for another 2–3 years.
Two crops per year are harvested in Sudan, the more abundant one after the rains in September, the other one in April. In India leaves are stripped or picked about 3 months after sowing. The second and third harvest follow after 4–6 weeks. At the third harvest the pods are harvested as well.
Yields of Senna alexandrina vary considerably depending on the soil and water conditions. In India the average annual yield is about 700 kg of leaves and 100 kg of pods per ha under rainfed conditions. Under irrigation the yield of leaves and pods is about 1400 kg/ha and 150 kg/ha, respectively. Although the sennoside content is higher when plants are under stress, moderate irrigation and fertilization pay off through increased leaf and total sennoside yields.
Handling after harvest
In Sudan the harvested plants are placed on rocks until thoroughly dry and are subsequently stripped of the leaves. The leaves curl when drying and are loosely packed. In India the leaves are dried on a clean floor indoors or under shade. The leaves are spread thinly and stirred regularly to promote uniform drying. The leaves are packed into bales after drying, using a hydraulic press. Good leaves are fresh and bright yellowish green, with a faint and peculiar odour like green tea and a mucilaginous, sweetish, slightly bitter taste. The pods are tied in bunches and hung in well-ventilated sheds to dry for 10–12 days. After threshing the seeds are separated from the pods. The pod material is usually packed in boxes. The leaves and pods retain their medicinal value for years if stored at low temperature and humidity, but should be powdered only as needed, because the powder tends to absorb moisture, become mouldy and lose value.
Although Senna alexandrina is harvested in Sudan from the wild in considerable quantities, this is not considered a threat to its genetic diversity in the country. The Central Institute of Medicinal and Aromatic Plants in Lucknow, India, holds a considerable number of Indian genotypes. The regional variation within the species is poorly captured in collections.
Selection in Senna alexandrina for a high number of branches offers opportunities to improve the dry leaf yield per plant.
The multitude of trade names of Senna alexandrina and a poor understanding of taxonomic classification and changing nomenclature lead to confusion. The opportunities for expansion of commercial cultivation in tropical Africa deserve to be looked into.
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Sources of illustration
• Serrato Valenti, G., 1971. Adumbratio florae Aethiopicae 22. Caesalpiniaceae - gen. Cassia. Webbia 26(1): 1–99.
Correct citation of this article:
Bosch, C.H., 2007. Senna alexandrina Mill. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
wild and planted
1, flowering branch; 2, infructescence.
Redrawn and adapted by Iskak Syamsudin
leafy branch with inflorescences
obtained from Th. Schöpke
obtained from Th. Schöpke