Aim: Study of morphology, histology, powder characteristic of Senna Leaf

Synonyms: cassia, sennai patti

Geographical Source: Cassia senna is aborigine of tropical Africa and Sudan while Cassia angustifolia is native to Arabia, Somalia, Sind and the Punjab (parts of India)

Macroscopy:

Senna plants are low branching shrubs (3 feet) with a straight woody stem and yellow flowers.

Leaflets of senna have stout petiolules, entire margin lamina with an asymmetric base and an acute apex. It has a characteristic odor (faint) and bitterish unpleasant taste.

Microscopy:

The transverse section of a senna leaflet exhibits isobilateral structure under the microscope.

The following tissues are observed in the lamina and midrib region:

A. Lamina:

i. Upper epidermis:

It is composed of polygonal cells arranged in a single layer, covered on the outer side with prominently thick, warty cuticle. Few epidermal cells contain mucilage and straight anticlinal walls. The epidermis bears only nonglandular covering trichomes which are unicellular, short, thick walled, conical, non-lignifi ed, warty and often curved at the bulbous base or with papillose walls. Paracytic stomata are seen at regular intervals.

ii. Mesophyll:

It is differentiated into palisade and spongy parenchyma. Isobilateral structure exhibits presence of upper palisade below the upper epidermis and lower palisade placed above the lower epidermis:

a. Upper palisade:

It is a single layer of elongated, narrow, columnar cells with chloroplastids. The upper epidermis also continues over the midrib region.

b. Spongy parenchyma:

It is made up of loosely arranged parenchymatous cells and contains rosette or prismatic crystals of calcium oxalate.

c. Lower palisade:

It extends to somewhat limited area, i.e. to the lamina region only. Cells are small and loosely arranged and have wavy walls.

d. Lower epidermis:

Cells possessing prominent cuticle and sunken stomata are seen. These cells are somewhat shorter than those of the upper epidermis and have slightly wavy walls. Non-glandular trichomes are also found on the lower epidermis.

B. Midrib:

The transverse section through the midrib region exhibits a fl at ventral surface and convex dorsal surface. The epidermal layers are in continuation over the midrib also. The lower epidermis possesses small cells with thick cuticle. The upper palisade is also made up of smaller cells particularly in the midrib region. The lower palisade is absent in the midrib portion, and a group of collenchymatous cells is seen.

At the centre, a group of collateral vascular bundles with xylem on the upper side and phloem beneath is seen. The vascular bundles are covered on both ventral and dorsal sides by an arc of lignified sclerenchymatous fibres. These patches of fibers are somewhat ovate in shape and crescent shaped below. This fibrous arc is characteristic as these fibers are encircled by a layer of parenchyma, with cells of most of it containing prisms of calcium oxalate crystals.

Fibres ensheathed with crystals can be seen occasionally in the lamina portion also. In the surface view, characteristic rubiaceous stomata, covering trichomes and polygonal epidermal cells are seen.

Calcium oxalate crystals:

These are abundant and seen as scattered in the powder. Prisms of calcium oxalate are seen inside the cells of the parenchymatous sheath surrounding the group of sclerenchymatous fibres, and rosettes are seen in the cells of spongy mesophyll. Rosettes (cluster crystals) are of moderate size.

d. Groups of fibres:

These are thick walled, lignified with few pits and encircled with a sheath of prisms of calcium oxalate.

e. Pieces of lamina in sectional view:

The palisade cells are seen under the upper epidermis and above the lower epidermis. Palisade cells under the upper epidermis are much elongated and straight walled. Palisade cells above the lower epidermis are short and have sinuous walls. Cells of spongy mesophyll which lie in between these two layers are rounded and contain abundant cluster crystals of calcium oxalate in them. Mucilage is present in many epidermal cells and gives red colour with solution of ruthenium red.

f. Fragments of spiral, annular and pitted vessels are also seen.

Chemical Tests

Difference between Alexandrian and Indian senna (Tinnevelly Senna)

· Treat powdered drug with acid solution and extract with ether. When the organic layer is treated with methanolic magnesium acetate solution Alexandrian Senna gives pink color in daylight, while Indian/Tinnevelly Senna gives orange color in daylight.

· The same solution above in UV light gives a pale greenish-orange color for Alexandrian Senna, while the Indian Senna gives a yellowish-green color.

Adulterants/Allied drugs/ Substitutes Allied drugs:

Arabian, Bombay and Mecca senna obtained from wild plants of Cassia Angustifolia resemble the leaflets of Tinnevelly senna but are of brownish-brownish green color and somewhat more elongated and narrower. Can be distinguished microscopically from other senna by their vein islet number.

Dog sennaderived from Cassia obovata have leaves obovate (ovate with the narrower end at the base) in shape and quite different from the official leaflets. Microscopically identified by the papillose cells of the lower epidermis.

Palthe senna obtained from Cassia auriculatacan be recognized by the long hair, absence of anthraquinone derivatives and the crimson color obtained on boiling it with chloral hydrate solution or with 80% H2SO4.

Substitutes and Adulterants:

Argel leaves derived from Solenostemma arghel were mixed historically with senna leaflets. These days it is classified as an adulterant and can be identified microscopically by the presence of 2 or 3 celled hairs, each surrounded by about 5 subsidiary cells.

In Nigeria, Cassia podocarpa is officially substituted.

Uses:

Senna is a useful laxative for either occasional use or habitual constipation. It is a popular laxative specially amongst the elderly and is devoid of the astringent after effects as observed in Rhubarb. It is reviewed to be useful during pregnancy and lactation.

Other Notes (life cycle, extraction etc.) –

Adverse Reactions Senna at times may cause little abdominal discomfort like cramping. Prolonged use can cause ‘laxative dependency syndrome’ resulting in poor bowel movement without the presence of a laxative and it also may cause alteration of electrolytes. Also overuse may result in colon pigmentation and reversible finger clubbing (enlarged finger ends and toe ends).