Alkaloids are bitter-tasting chemicals, very widespread in nature, and often toxic, found in many medicinal plants, ⁸. There are several classes with different modes of action as drugs, both recreational and pharmaceutical. Medicines of different classes include atropine, scopolamine, and hyoscyamine (all from nightshade), ^{9, 10}.

Anthraquinone glycosides are found in medicinal plants such as rhubarb, cascara, Aloe and Alexandrian senna, ^{9, 11, 12, 13}. The cardiac glycosides are powerful drugs from medicinal plants including foxglove and lily of the valley. They include digoxin and digitoxin which support the beating of the heart, and act as diuretics, ⁵.

Polyphenols of several classes are widespread in plants, having diverse roles in defenses against plant diseases and predators, ⁵. They include hormone-mimicking phytoestrogens and astringent tannins, ^{9, 14}. Plants containing phytoestrogens have been administered for centuries for gynecological disorders, such as fertility, menstrual, and menopausal problems, ^{15, 16, 17, 18, 19}.

Terpenes and terpenoids of many kinds are found in a variety of medicinal plants, ¹⁸ and in resinous plants such as the conifers. They are strongly aromatic and serve to repel herbivores. Their scent makes them useful in essential oils, whether for perfumes such as rose and lavender, or for aromatherapy, ^{9, 20, 21}. Some have medicinal uses: for example, thymol is an antiseptic and was once used as a vermifuge (anti-worm medicine), ²¹.

S. occidentalis is an annual too short-lived perennial herb to small shrub with a pantropical distribution. It is reported as invasive throughout Oceania, and various countries in Asia and Africa. Within its native range S. occiden-alis is listed as invasive for Cuba by Oviedo Prieto et al. ²². The scientific name is Senna occidentalis with a common name as Coffee Senna.

Domain: Eukaryota

Kingdom: Plantae

Phylum: Spermatophyta

Subphylum: Angiospermae

Class: Dicotyledonae

Order: Fabales

Family: Fabaceae

Subfamily: Caesalpinioideae

Genus: Senna

Species: Senna Occidentalis

The morphology of S. occidentalis as described by Parsons and Cuthbertson ²³, closely matches that as described in other places in the world. It is a low growing, sparsely branching annual or short-lived perennial plant up to 0.5-2 m high and having a characteristic fetid odour. The stems are reddish purple, erect, 4-angled when young, becoming rounded with age. The plant has a robust primary root with several laterals. The leaves are pale green on reddish stalks; alternate, pinnate, with 3-5 (sometimes 6) pairs of opposite ovate to lanceolate-elliptic leaflets, 25-100 mm long, 20-30 mm wide, rounded at the base. A conspicuous, dark-coloured gland occurs at the base of the petiole (leaf stalk) but not on the stalks of the leaflets. The flowers are pale to bright yellow, 20-30 mm in diameter, in 2-6 flowered axils of the upper leaves; sepals are red veined; 5 petals per flower, the 2 anterior ones are smaller than the others; fertile stamens 6, the two basal ones longer than the rest, 4 infertile stamens are reduced to tiny petal-like staminodes. Further descriptions of the floral anatomy of S. occidentalis and nine other species of Cassia are given by Chhavi-Thakur and Thakur ²⁴. The fruit is a dark brown, flattened, sickle-shaped pod with paler stripes along the edges when mature. Pods are 75-130 mm long, 8-10 mm wide, containing a single row of 25-35 seeds. The seeds are dark brown, flattened, hard, 5 mm long and 3 mm wide. Plate 1

Plate 1. Close view of senna occidentalis in its natural habitat

Phytochemical screening of the plant showed the presence of carbohydrates, saponins, sterols, flavonoids, resins, alkaloids, terpenes, anthraquinones, glycosides and balsam. Presence of these metabolites strongly concluded the great potential of the plant as a source of phytomedicines. As the flavonoids and resins are present, it might be responsible for its anti-inflammatory properties. Chinese folkloric medicine contains flavonoids which has anti-inflammatory effect on both acute and chronic inflammation, alkaloids for blood pressure decrease and nervous system balancing, Tannins for wound healing and terpenes with anti-viral properties, ^{25, 26, 27}.

Eudesmane sesquiterpenes have been reported to contain antibacterial properties. Saponins are believed to have antioxidant, anti-cancer, anti-inflammatory, and anti-viral properties. The anthraquinones, emodin and chrysophanone have been reported to possess wound healing properties. Other compounds reported in literature include, 1,8-dihydroxyl-2-methyl anthraquinone, 1,4,5-trihydroxy-3-methyl-7-methoxy anthraquinone, cassiaoccidentalin A, B and C, which are C-glycosides, achrosine, anthrones, apigenin, aurantiobtusin, campesterol, cassiollin, chryso-obtusin, chrysophanic acid, chrysarobin, chrysoeriol, essential oils, funiculosin, galactopyranosyl, helminthosporin, islandicin, kaempferol, lignoceric acid, linoleic acid, linolenic acid, mannitol, mannopyranosyl, matteucinol, obtusifolin, obtusin, oleic acid, physcion, quercetin, rhamnosides, rhein, rubrofusarin, sitosterols, and xanthorin ^{28, 29}. Figure 1

Figure 1. Structures of some compounds isolated from Senna occidentalis

To each 0.5 g of sample in 20 mL test tube was added chloroform (1 mL) and also few drops of acetic anhydride were added followed by concentrated H₂SO₄. The mixture was mixed carefully and a blue colour that changed with time was observed in the resulting solution which indicated the presence of steroids/terpenes ³².

To each 0.5 g of sample in a 20 mL test tube chloroform (1 ml) was added and to it 1 mL of concentrated H₂SO₄ was added down the test tube to form two phases. Formation of yellow coloration was taken as that which indicates the presence of sterols ³².

To 1 g of the sample in 20 mL test tube was added methanol (5 mL). Also, to the sample was added three pieces of magnesium chips followed by few drops of concentrated HCl. A purple colour was observed which indicated the presence of flavonoids ³¹.

Little quantity of the extract was dissolved in 1 mL concentrated sulfuric acid and a colour change was observed which indicated the presence of flavonoids ³².

A small quantity of the extract was dissolved in water and filtered. Few drops of 10 % lead acetate were added to 5 mL of the filtrate. A buff colored precipitate indicated the presence of flavonoids ³³.

To 1 g sample in 100 mL beaker was added 10% aqueous sodium hydroxide solution (5 mL) and filtered to give yellow color, a change in color from yellow to colorless on addition of dilute HCl was observed which indicated the presence of flavonoids ³⁴.

To 1 g of sample in 20 mL test tube was added 5 mL of distilled water and boiled and the mixture was filtered. Two drops of ferric chloride were added to the filtrate, formation of green precipitate was observed which indicated the presence of tannins ³⁵.