423

12(1): Medicinal and poisonous plants 1

Senna Miller

Gard. Dict. abr. ed. 4, vol. 3 (1754).

LEGUMINOSAE

x = 11, 12, 13, 14; Senna alata: 2n = 28, Senna garrettiana: 2n = 28, Senna sophera: 2n = 28

Major species Senna alata (L.) Roxb., Senna sophera (L.) Roxb., Senna tora (L.) Roxb.

Malaysia: bebusok. Cambodia: angkanh. Laos: khi lek. Vietnam: mu[oof]ng.

Senna comprises about 260 species and has a pantropical distribution; a few species extend to temperate regions. Tropical Asia has far fewer Senna species than tropical America, Africa and Australia. Only about 7 species occur naturally in tropical Asia, and only about 5 in the Malesian region, including Senna tora. Approximately 10 species have been introduced in Malesia and have become naturalized or even weedy (e.g. Senna alata and S. sophera) others are planted as ornamentals and are only rarely found as escapes. Senna garrettiana (Craib) Irwin & Barneby, which is an important medicinal species, is endemic to Indo-China and northern Thailand.

The main medicinal uses of Senna in South-East Asia are in the treatment of skin problems and as a laxative or purgative. Skin problems treated with Senna include ringworm (e.g. Senna alata, Senna garrettiana, Senna hirsuta (L.) Irwin & Barneby, Senna occidentalis (L.) Link, Senna sophera and Senna tora), scabies (e.g. Senna alata, Senna timoriensis (DC.) Irwin & Barneby), eczema (Senna hirsuta, Senna occidentalis) and itching (Senna alata, Senna timoriensis). Laxative properties have been reported for Senna alata, Senna garrettiana, Senna obtusifolia (L.) Irwin & Barneby, Senna occidentalis, Senna siamea (Lamk) Irwin & Barneby, Senna surattensis (Burm. f.) Irwin & Barneby and Senna tora.
The wood of Senna alata, Senna garrettiana and Senna siamea is included in recipes for decoctions to treat liver problems, urticaria, rhinitis and loss of appetite caused by gastro-intestinal problems. The heartwood of Senna garrettiana is the Thai drug 'Sae mae sarn', which is used as a mild purgative. Senna siamea and Senna timoriensis are used as vermifuge. In Indonesia, a decoction of young Senna siamea leaves has been suggested for the treatment of malaria. In Burma (Myanmar), leaves, flowers and fruits of Senna siamea are ingredients of a broth which is used as a tonic and to treat stomach problems. In Thailand, the heartwood of Senna siamea is considered as a tranquillizer, antipyretic, and used in the treatment of venereal diseases; the leaves are used in the treatment of leucorrhoea; antihypertensive and antipyretic properties are ascribed to the flowers. The leaves of Senna obtusifolia are used against vomiting and stomach-ache. The leaves of Senna occidentalis are used in cases of toothache and headache. The seeds act as an emeto-cathartic and in the Philippines are used to treat fever. A decoction of the roots of Senna surattensis is used against gonorrhoea, a decoction of the leaves is used against dysentery.
The bark of Senna alata contains tanning material; the seeds are a promising source of gums. The bark of Senna auriculata (L.) Roxb. is used as a source of tannin, but the astringent properties are also of medicinal importance. Toasted leaves of Senna alata and the seeds of Senna tora are sometimes used as a coffee substitute. The young pods of Senna alata and the young leaves of Senna tora may, in small quantities, be eaten as a vegetable. In West Africa, the roots of Senna tora are used for tattoos or tribal markings.

Many of the pharmacological effects of Senna species can be attributed to the presence of anthraquinone derivatives. The basic structure of these compounds is the 9,10-anthraquinone. They differ in the arrangement of the attached substituents. The derivatives may occur in various oxidation stages; anthraquinones can be reduced to anthrones, which may be oxidized to dianthrones. Dianthrones, on the other hand, can be reduced back to anthrones, which may oxidize to anthraquinones relatively easily.
Anthraquinone and dianthrone drugs are used as laxatives. The presence of sugar in the molecule is a prerequisite for their pharmacological action; it enhances their solubility in water, thus facilitating their transport to the site of action (the colon).
Bacteria in the colon hydrolyse the glycosides and dianthrones to anthraquinones, a reaction which is immediately followed by the local reduction of the anthraquinones to their corresponding anthrones. The latter compounds act directly on the large intestine, to stimulate peristalsis. However, laxative drugs containing anthraquinone derivatives should be used with caution, as daily and prolonged use can lead to dependence and 'cathartic colon'.
In anthrones, the explicit chemical structure is very reactive. An imperfectly understood mechanism enables these compounds to completely inhibit cell growth and thymidine incorporation in human cultured cells, and inhibit both DNA replication and repair synthesis. Because of these effects on the cell cycle, anthrones may be used as topical agents in the treatment of psoriasis. Their (topical) use in the treatment of skin infections, and their fungicidal properties (treatment of ringworm) have also been reported in the literature. Furthermore, their reactiveness makes these compounds very irritant to the eyes and mucous membranes; they should never be used systemically.
Extensive phytochemical investigations have revealed much information about the constituents of several Senna species. Components isolated from the leaves of Senna alata include the anthraquinone derivatives rhein (cassic acid), rhein-anthrone and aloe-emodin-anthrone, and flavonoids (e.g. kaempferol, glycosides). The yellow phenolic pigment cassiaxanthone has been isolated from the roots. Senna sophera has been reported to contain the anthraquinones chrysophanol (chrysophanic acid) and emodin.
The reported constituents from Senna tora seeds include anthraquinone derivatives (emodin, physcion, chrysophanol (chrysophanic acid), chrysophanol-triglucoside, chrysophanol-tetraglucoside, chryso-obtusin, aurantio-obtusin and obtusifolin-glucoside), naphtho-'GAMMA'-pyrones (cassiaside, rubrofusarin-gentobioside, rubrofusarin-glycoside), toralactone-gentobioside (a naphtho-'ALFA'-pyrone), cassitoroside (a naphthalene glycoside) and 'BETA'-sitosterol (a sterol). Senna tora also contains the flavonoid glycoside kaempferol-3-sophoroside. Anthraquinone derivatives (chrysophanol (chrysophanic acid), chrysophanol benzanthrone, chrysophanol dianthrone, cassialoin, (-)-11-deoxyaloin), bibenzyl derivatives, flavonoids, stilbene derivatives and polyphenolic compounds (cassigarol A-G, scirpusin B) have been isolated from the heartwood of Senna garrettiana. Seeds of several Senna species (including Senna alata, Senna hirsuta, Senna occidentalis, Senna siamea and Senna tora) are reported to contain the enzyme urease.
Some other pharmacological activities of anthraquinone derivatives and other Senna constituents in addition to the purgative effect are mentioned in the literature. In an assay with Salmonella typhimurium the methanol extract of Senna tora seeds showed antimutagenic activity against aflatoxin B1. The numbers of revertants per plate decreased significantly when this extract was added to the assay system. The extract was not able to inhibit the direct-acting mutagen N-methyl-N'-nitro-N-nitrosoguanidine; this suggests that it may prevent the metabolic activation of aflatoxin B1 or scavenge the electrophilic intermediate capable of inducing mutations. Activity guided isolation yielded the anthraquinones chrysophanol (chrysophanic acid), chryso-obtusin and aurantio-obtusin, and the naphtho-'GAMMA'-pyrones cassiaside and rubrofusarin-gentobioside as pure compounds. All of these demonstrated significant antimutagenic activity.
Senna alata extracts have shown antibacterial and antifungal properties (e.g. against Pityriasis versicolor in humans) and anti-tumour activity; they might be useful in the treatment of opportunistic infections in AIDS patients. Leaf extracts of Senna tora also have antifungal activity. The major antifungal principle has been shown to be chrysophanol-anthrone (chrysophanic acid-anthrone), which is also present in the seeds.
Furthermore, the polyphenol cassigarol A (from Senna garrettiana) inhibits H⁺/K⁺-ATPase, resulting in a reduced gastric acid secretion. The flavonoid glycoside kaempferol-3-sophoroside (from Senna tora) has analgesic activity, as has been shown by intraperitoneal injections in mice and rats. Naphtha-pyrone glycosides in Senna tora seeds have been found to protect the liver against galactosamine damage. The leaves of Senna siamea exhibits central nervous system depressant effects, and the compound responsible for the activity is barakol.
Raw Senna tora seeds have furthermore been found to be highly toxic in experiments with rats; pigs fed on leaves and pods of Senna siamea in the Philippines died.

It is reported that in China Senna occidentalis, Senna sophera, Senna tora and Chamaecrista mimosoides (L.) Greene are used medicinally almost without distinction. Anthraquinone glycosides and sennosides are also found in Cassia species, which are also used for their laxative and purgative properties.

Herbs, shrubs or small to medium-sized trees up to 20(-30) m tall; bole usually short, up to 50 cm in diameter, bark surface smooth, greyish. Leaves alternate, paripinnate with up to 24(-40) pairs of leaflets, sometimes with extra-floral nectaries; stipules small, usually caducous. Inflorescence an axillary raceme, often becoming corymbose-paniculate towards the tips of branchlets, 1-many-flowered. Flowers bisexual, 5-merous; sepals imbricate, obtuse at apex; corolla with subequal to heteromorphic petals, yellow; androecium basically 10-merous, filaments all straight and never more than twice as long as anthers, accrescent towards the abaxial side of the flower; ovary superior, linear and curved. Fruit a stipitate, often strap-shaped, terete to compressed, indehiscent or inertly dehiscent pod, usually with septae between the numerous seeds. Seeds with distinct areole. Seedling with epigeal germination; cotyledons emergent, semi-fleshy.

Senna alata has Scarrone's architectural model: an indeterminate trunk with tiers of orthotropic branches, which branch sympodially because they have terminal inflorescences. Most of the medicinally important Senna species are reported to flower and fruit throughout the year, though fluctuations occur in pronounced monsoon climates. Growth of Senna tora is affected by photoperiod, and pods are only produced when plants receive 8-11 hours of light. Flowers are produced at 6-12 hours of light.

Until the beginning of the 1980s Cassia was considered to be a very large genus of over 500 species, but then it was split into 3 genera: Cassia sensu stricto, Senna and Chamaecrista. Cassia now has only about 30 species, whereas Senna and Chamaecrista comprise about equal numbers of species (about 260 and 270 respectively). Senna tora is closely related to Senna obtusifolia, which is similar in appearance, but Senna obtusifolia can easily be recognized by its longer pedicels. Senna sophera is closely related to Senna occidentalis, and the two are often confused.

In South-East Asia, Senna alata, Senna sophera and Senna tora are found in a multitude of habitats, but preferably in disturbed, rather open (anthropogenic) vegetation: roadsides, river banks, rain forest edges, lake shores, margins of ponds and ditches, in open forest and wet areas, in orchards and around villages. Senna alata is found up to 1400(-2100) m altitude but is more common at lower elevations. The other species are only found at lower elevations: Senna sophera up to 400 m and Senna tora up to 1000 m altitude. Senna alata and Senna tora are reported to tolerate an annual rainfall from 600 mm to 4300 mm and average yearly temperatures of 15-30°C. Soils should retain moisture adequately, although Senna tora is tolerant of considerable drought, whereas the pH may range between 4.3-8.0.

Senna can be propagated by seed. Propagation by stem and root cuttings has not been successful. Senna tora has hard seeds and mechanical and acid scarification are equally effective in breaking dormancy. Senna tora germinates in continuous light or darkness and under alternating light conditions. No germination occurs below 13°C or above 40°C. Seed stored at 15-20°C germinates when scarified and placed in a 30°C environment. The stage of maturity at harvest affects seed viability and germination. In dry storage seed loses viability somewhat rapidly (germination 22% after 3 years). Germination is optimal when soil moisture is 75% of field capacity. Shoot and root dry matter production diminish at densities above 20 plants/m². The number of flowers and fruits per plant drop at densities between 10 and 20 plants/m². The average number of seeds/m² increases from about 40 (1 plant/m²) to a maximum of about 570 (17 plants/m²); it drops to about 145 at a density of 40 plants/m².

Anthraquinones have been obtained from plant cell cultures of Senna tora, with yields of 0.33% of the fresh weight.

In Indonesia, brown leaf blight caused by Cercospora sp. is reported on Senna alata. In Uganda, common bean mosaic necrosis virus has been isolated from Senna sophera. In India, Senna tora is reported to be attacked by the defoliator Myllocerus viridanus and the bruchids Callosobruchus chinensis, Bruchidius cassiae and Caryedon lineatonota. The seed bruchid Sennius instabilis has been suggested as a potential biological agent for controlling Senna tora in pastures.

The leaves of Senna alata are harvested when needed. The active constituents are probably most abundant prior to flowering, which is why the leaves are preferably collected at that time. The pods of Senna tora are collected when mature.

After harvesting, Senna alata leaves are dried and sometimes stored in containers until needed. The mature pods of Senna tora are sun-dried; prior to use the seeds are removed and roasted.

Senna alata, Senna sophera and Senna tora are widely found wild and cultivated in and outside South-East Asia, and they are neither endangered nor liable to genetic erosion.

As Senna species have various medicinal properties, ornamental value, and are used for various other purposes, they are true multipurpose plants. The antifungal and anti-tumour properties seem to justify more research.

Baba, K., Kido, T., Taniguchi, M. & Kozawa, M., 1994. Stilbenoids from Cassia garrettiana. Phytochemistry 36(6): 1509-1513.
Boer, E. & Lemmens, R.H.M.J., 1998. Senna Mill. In: Sosef, M.S.M., Hong, L.T. & Prawirohatmodjo, S. (Editors): Plant Resources of South-East Asia No 5(3). Timber trees: Lesser-known timbers. Backhuys Publishers, Leiden, the Netherlands. pp. 522-524.
Bruneton, J., 1995. Pharmacognosy, phytochemistry, medicinal plants. Lavoisier Publishing, Paris, France. pp. 349-366.
Bulyalert, D., 1993. Effect of barakel on the central nervous system: qualitative analysis of BEG in the rat. Chiangmai Medical Bulletin 32(4): 191-196.
Burkill, I.H., 1966. A dictionary of the economic products of the Malay Peninsula. Revised reprint. Vol. 1. Ministry of Agriculture and Cooperatives, Kuala Lumpur, Malaysia. pp. 478-488.
Faridah Hanum, I. & van der Maesen, L.J.G. (Editors), 1997. Plant Resources of South-East Asia No 11. Auxiliary plants. Backhuys Publishers, Leiden, the Netherlands. pp. 229-236, 294-295.
Hata, K., Baba, K. & Kozawa, M., 1979. Chemical studies on the heartwood of Cassia garrettiana Craib. II. Nonanthraquinonic constituents. Chemical and Pharmaceutical Bulletin 27(4): 984-989.
Holm, J., Doll, J. & Holm, E., 1997. World weeds: natural histories and distribution. Wiley, New York, United States. pp. 158-171.
Larsen, K. & Ding Hou, 1996. Senna. In: Kalkman, C., Kurkop, D.W., Nooteboom, H.P., Stevens, P.F. & de Wilde, W.J.J.O. (Editors): Flora Malesiana. Series 1, Vol. 12(2). Rijksherbarium/Hortus Botanicus, Leiden University, the Netherlands. pp. 673-691.
Nguyen Van Duong, 1993. Medicinal plants of Vietnam, Cambodia and Laos. Mekong printing, Santa Ana, California, United States. pp. 92-96.

Anny Victor Toruan-Purba

Senna alata
Senna sophera
Senna tora

Toruan-Purba, A.V., 1999. Senna Miller. In: de Padua, L.S., Bunyapraphatsara, N. and Lemmens, R.H.M.J. (Editors): Plant Resources of South-East Asia No 12(1): Medicinal and poisonous plants 1. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea

The following species in this genus are important in this commodity group and are treated separatedly in this database:
Senna alata
Senna sophera
Senna tora