Pharmacognostical evaluation of leaf of Bada Rasna [Nelsonia canescens (Lam.) Spreng.; Acanthaceae].

Nelsonia canescens (Lam.) Spreng. (Acanthaceae), a well-known plant in traditional systems of medicine, known as "Bada Rasna" by the traditional practitioners of Odisha, is being used as Rasna for managing pain and inflammation. The detailed macroscopic and microscopic characters of the plant, except its root, are lacking. Hence, it was thought worth to study the leaves of the plant for its detailed morphological and microscopical characters, by following the standard pharmacognostical procedures. The study shows the presence of diacytic stomata in the lower epidermis of lamina, microsphenoidal and prismatic crystals of calcium oxalate in the mesophyll cells, simple and glandular trichomes. The observed major diagnostic characters of the leaf may find useful for its standardization.

INTRODUCTION

Nelsonia canescens (Lam.) Spreng. of the family Acanthaceae, is a small trailing delicate herb with long underground root and aerial spreading stem with plenty of leaves and the traditional healers use the root, fruit, and leaves of the plant for different disease conditions.[12] This plant, known as “Bada Rasna,” by the traditional practitioners of Odisha, is used as a source plant of Rasna.[3] Its root is reported for its anti-inflammatory and analgesic[4] and whole plant for its hepatoprotective action.[5] N. canescens is also reported to be used as a cover crop to suppress weeds in banana plantations.[6] Detailed macroscopic and microscopic characters of the root have been reported earlier.[7] Detail investigation about the morphological and microscopical evaluations of its leave, though claimed to be a part used, is lacking. Hence, leaves of this plant were selected for the present study. Detailed morphological and microscopical evaluations of the leaves were thought to be study for the correct identity of this plant.

MATERIALS AND METHODS

Collection and authentication

The plant commonly known by tribal people as “Bada Rasna” is growing in Gandhamardana Hills ranges, Balangir of Odisha District of India.[8] It was identified as N. canescens Lam. Spreng of family Acanthaceae by studying the morphological characters of various parts of the plant and comparing them with the various characters mentioned in various floras.[8-12] The plants were shaken to remove adherent soil, dirt, etc. or washed with water and herbarium specimen was prepared (Herbarium No. 6002) and was stored in Pharmacognosy Department of the Institute for further documentation. The leaves were separated from the stem, washed with running fresh water and few pieces were stored in solution of AAF (70% ethyl alcohol:glacial acetic acid:formalin) in the ratio of (90:5:5).[13] To utilize them for microscopic studies whenever needed. The remaining leaves were dried under the shade and then were subjected for 60# powdering.

Pharmacognostic studies

Morphological characters were studied by observing the leaves as such and also with the help of the dissecting microscope. For showing the arrangements of tissues of the whole section of the leaf was taken and cleared with chloral hydrate. For detailed microscopical observation, thin transverse sections passing through the midrib were taken and cleared with chloral hydrate and observed as such for the presence of any crystals, then were stained with phloroglucinol and hydrochloric acid to notice the lignified element like fibers, vessels, etc., of the meristel and other parts. The section was drawn with the help of camera lucide. Photographs of the sections were also taken with the help of canon Ixus 130 camera. The sections were stained with various reagents like phloroglucinol + HCl for lignified elements.[14]

Quantitative microscopy

Determination of certain leaf constants like palisade ratio, stomatal number, stomatal index and vein islet number were carried out as per the method described in Ayurvedic Pharmacopoeia of India.[14]

RESULTS AND DISCUSSION

Macroscopical characters

Leaves simple, easily breakable, lanceolate to ovate lanceolate in shape, 16-17 cm in length and 10-11 cm in width, brittle, margin broadly crenate, apex acute to obtuse, base symmetrical, venation reticulate, midrib prominent at the lower surface, lateral veins runs almost parallel and placed at an acute angle, surface rough highly pubescent and protruding at lower surface, Petiole cylindrical and petiole of lower leaves up to 4cm, bitter and pungent in taste with characteristic odor [Figure 1a and b].

Figure 1

Nelsonia canescens leaf photos (a-h) Enlarged view of various parts of the leaf.

Acr- Acicular crystal, Cam-Cambium, Col- Collenchyma, Cu-Cuticle, Le-Lower Epidermis, Mcr-Microsphenoidal crystal, Mr-Medullary, Ue- Upper epidermis, Xy-Xylem Vessel

Microscopical characters

The diagrammatic transverse section passing through the midrib is strongly convex at the lower side and with slight elevation at the upper side, shows collenchymatous band underneath both epidermis and a centrally located arc of meristele with lateral narrow laminar extensions on its either sides [Figure 2a].

Figure 2

Nelsonia canescens leaf drawn photo

Detailed section passing through the midrib shows a layer of small sized, radially elongated cells, covered with thin cuticle and bearing simple and glandular trichomes, they being plenty on the lower side. Simple trichomes are multi cellular, uni-serrate and are very long. Glandular trichomes are sessile with multi cellular globular head and few with unicellular stalk. Underneath both the epidermis lies well developed 4-5 rows of collenchymatous cells. An arc of meristele embedded in the centre of the midrib shows rows of vessels and dorsiventrally placed phloem tissue embedded with isolated or groups of fibers usually arranged in rows, 1-2 rudimentary vascular bundles are occasionally seen on the upper side of the arc. Ground tissue is parenchymatous and embedded with acicular and microsphenoidal crystals of calcium oxalate.

Lamina shows upper and lower epidermis enclosing a narrow band of mesophyll tissue. Upper epidermis consists of radially elongated, broad rectangular cells devoid of stomata, covered with thin cuticle and bearing large number of various trichomes as described under the heading of powder characters. The cells of the lower epidermis are smaller in the size than upper epidermis and are embedded with stomata. At places, the epidermis gets slightly elevated and shows a small cavity embedded in the tissue lying underneath it. 2-3 rows of very small sized compactly placed palisade cells are located underneath upper epidermis. Remaining 3-4 rows of cells being of spongy parenchyma embedded with the vascular bundle. Acicular crystals and microsphenoidal crystals are embedded throughout the parenchymatous cells of the section [Figure 1c–h].

Powder characteristics

Powder of leaf is greenish in color having characteristic odor and astringent bitter taste. The diagnostic characters of the powder are:

Fragments of upper and lower epidermis in surface view. The cells of the upper epidermis are straight walled and hexagonal in shape, they being bigger in size devoid of stomata and at places shows underlined palisade cells in the upper side; unlike the lower epidermis which are smaller in size, embedded with dicytic stomata.

Plenty of simple and glandular trichomes of various shape and sizes scattered as such throughout or attached with the parenchymatous cells of the epidermis. Simple unicellular trichomes are short, warty, conical, while the multicellular trichomes are long, at places with collapsed cell, straight or slight bent, thick walled, glandular trichomes are mostly sessile with 2 to 4 celled head or with a short unicellular stalk and uni- to bi-cellular head; fragments of annular and spiral vessels.

Transversely cut fragments of lamina with the upper epidermis and rows of underlined small-sized palisade cells and spongy parenchyma embedded with acicular, prismatic and microsphenoidal crystals of calcium oxalate.

The quantitative microscopical data is as follows:

Stomatal number and stomatal index of the lower epidermis is 9 and 24.3, upper epidermis is devoid of stomata, palisade ratio is 12-13, vein islet number is 20, and vein termination number is 0, respectively [Figure 2b].

CONCLUSION

Leaves of Nelsonia canescens (Lam.) Spreng can be identified by the presence of diacytic stomata in the lower epidermis of lamina, microsphenoidal and prismatic crystals of calcium oxalate in the mesophyll cells, simple and glandular trichomes.