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          Centella is the dried aerial part of Centella asiatica (L.) Urb. (C. coriacea Nannf., Hydrocotyle asiatica L., H. lunata Lam., Trisanthus cochinchinensis Lour.) (Family  Umbelliferae), Herbarium Specimen Number:  DMSC 1461, Crude Drug Number:  DMSc 1261. 

Constituents  Centella contains triterpenoid saponins, including asiaticoside and madecassoside and their aglycones which are asiatic acid and madecassic acid, respectively.  It also contains volatile oil, pectin, trace of alkaloids, etc.

Description of the plant  (Figs. 1a, 1b)  Slender trailing herb, rooting at nodes.Leaves simple, 1 to 6 in rosette at each node, orbicular to reniform, more or less cupped, glabrous and shiny above, paler beneath,1 to 7 cm in diameter, apex rounded, base cordate, margin entire, crenate, or usually repand-dentate; petiole (1–)4 to 10(–50) cm long.  Inflorescence in single umbel, bearing solitary or 2 to 5 together in the axils; peduncle shorter than petiole. Flowers usually 3, middle one sessile, lateral ones pedicellate; involucres 2, ovate; petals 5, minute, white or rose-tinged; ovary laterally flattened, style filiform.  Fruit small, compressed, about 8 mm long, orbicular to ellipsoid, manifestly ribbed, slightly hairy when young.

Description  Odour, characteristic; taste, slightly bitter-sweet.

          Macroscopical  (Fig. 1a)  Aerial part, greenish brown, rough and brittle; stem thin, long, twisted; leaves rennate or cordate, brittle; petiole long.

          Microscopical  (Figs. 2a, 2b, 2c, 2d) Transverse section of the fresh leaf shows upper epidermis, a layer of rectangular cells, polygonal and straight-walled in surface view; stomata, anisocytic, some paracytic and rarely anomocytic.  Palisade cells, a layer of large columnar cells.  Spongy cells, parenchymatous, some containing calcium oxalate crystals in the forms of rosette aggregate or prism.  Collenchyma, occurring beneath upper and lower epidermises in the midrib.  Vascular bundles, xylem in the upper part and phloem in the lower part; vessels, annular, spiral, scalariform, or reticulate. Lower epidermis, a layer of rectangular cells, slightly wavy-walled in surface view; stomata, anisocytic, paracytic or anomocytic. Oil ducts, occurring beneath collenchyma in the middle of midrib.   

          Transverse sections of the fresh petiole and stolon show epidermal layer with cuticle.  Collenchyma, present.  Parenchyma containing chloroplastids, oil droplets, spreading circularly beneath collenchyma.  Vascular bundles, collateral.  The centre of petiole, hollow.  Unicellular trichomes may also be found, but rare, in the section near the base of petiole.

          Centella in powder possesses the diagnostic microscopical characters of the unground drug.

Warning  Excessive oral administration should be avoided during pregnancy and lactation.

Packaging and storage  Centella shall be kept in well-closed containers, protected from light, and stored in a dry place. 

Identification

          A. Warm 500 mg of the sample, in powder, with 5 mL of ethanol for 5 minutes and filter (solution 1).  To 2 mL of solution 1, add a few drops of sulfuric acid:  a green colour develops.

          B. Evaporate 2 mL of solution 1 to dryness and dissolve the residue in 2 mL of acetic anhydride.  Add slowly 1 mL of sulfuric acid to form two layers:  a green colour develops in the upper layer and a brownish red ring forms at the zone of contact.

          C. Shake vigorously 500 mg of the sample, in powder, with 10 mL of water:  a long  lasting foam is produced.

          D. Carry out the test as described  in the “Thin-Layer Chromatography” (Appendix 3.1), using silica gel G as the coating substance and a mixture of 60 volumes of chloroform, 28 volumes of methanol and 4 volume of water as the mobile phase.  Apply separately to the plate, 5 µL each of the following solutions.  Prepare solution (A) by refluxing 1 g of the sample, in powder, with 20 mL of ethanol for 10 minutes and filtering.  Evaporate the filtrate under reduced pressure at 40° until dryness, and dissolve the residue in 4 mL of ethanol.   For solution (B), dissolve 1 mg of asiaticoside in 2 mL of ethanol.  For solution (C), dissolve 1 mg of asiatic acid in 2 mL of ethanol.  After removal of the plate, allow it to dry in air.  Spray the plate with anisaldehyde TS and heat at 105° for 5 minutes.  The chromatogram obtained from solution (A) shows a purple spot (hR_f value 27 to 28) and a violet spot (hR_f value 72 to 74) corresponding to the asiaticoside and the asiatic acid spots from solutions (B) and (C), respectively.  Several other spots of different colours are observed (Table 1); see also Fig. 3.

Table 1 hRf Values of Components in Ethanolic Extract of the Aerial Parts of Centella asiatica (L.) Urb.

*asiaticoside

Loss on drying  Not more than 14.0 per cent w/w after drying at 105° to constant weight (Appendix 4.15).

Foreign matter  Not more than 2.0 per cent w/w (Appendix 7.2). 

Acid-insoluble ash  Not more than 7.0 per cent w/w (Appendix 7.6). 

Total ash  Not more than 17.0 per cent w/w (Appendix 7.7).

Ethanol-soluble extractive  Not less than 15.0 per cent w/w (Appendix 7.12).

Water-soluble extractive  Not less than 24.0 per cent w/w (Appendix 7.12).

Dose  0.6 g three times a day.