Proper identification, quality assurance, and establishing pharmacognostic standards are very significant factors for evaluation of medicinal plants. According to the World Health Organization (WHO), the macroscopical and microscopical account of a medicinal plant is the first step towards ascertaining the identity and the degree of purity of such material and should be accomplished before any tests are undertaken [6, 13].
Microscopic assessment of the plant material is crucial for the detection of source materials. The anatomical attributes are employed as a criterion for unraveling the species, genera, and even families. Also, anatomy gives the idea of diagnostic features of a plant material such as cork cells, cortex, secondary phloem, and fibers which forms the vital factors for the quality control and standardization of herbal drugs [18]. Investigations of the powdered plant material offer the comprehensive structural information of the raw drugs by discovering the identified histological characters in the drugs. The powdered examination of herbal material is based on the cyto-morphological parameters, for instance collenchyma, parenchyma, trichomes, vessels, and secretory cells, and cell inclusions, viz., pollen grains, starch grains, and calcium oxalate crystals [19, 20].
Physicochemical parameters are also vital for the standardization and quality control of herbal drugs which included foreign matter analysis, loss on drying, ash content, pH, swelling index, and foaming index. Herbal materials should be devoid of any kind of contamination, so foreign matter analysis of powdered drugs can be considered as an important parameter in order to check the purity of herbal drugs [21]. Loss on drying is commonly used test procedure for determination of moisture content in a powdered sample. Moisture content of drugs should be at minimal level to discourage the growth of bacteria, yeast, or fungi during storage [22]. Ash values are used to determine quality and purity of crude drug. It indicates presence of various impurities like carbonate, oxalate, and silicate. The water soluble ash is used to estimate the amount of inorganic compound present in drugs. The acid insoluble ash consist mainly silica and indicate contamination with earthy material [22]. The pH values provide information about acidic or basic nature of the chemical constituents present in the crude drug. Foaming index is seen to be less than 100 in all the parts of the select species which reveals absence or very little amount of saponins. Swelling index indicates the presence of gums and mucilage, hemicellulose, or pectin in the natural drug [21]. Estimation of extractive values determines the amount of the active constituents in a given amount of plant material when extracted with a particular solvent. The extractions of any crude drug with a particular solvent yield a solution containing different phytoconstituents. The compositions of these chemical constituents depend upon the nature of the drug and the solvent used. It also provides an indication whether the crude drug is exhausted or not [22, 23]. Fluorescence analysis is also an important pharmacognostic parameter. Some constituents show fluorescence in the visible range in daylight. The ultraviolet light produces fluorescence in many natural products which do not visibly fluoresce in daylight. If substance themselves are not fluorescent, they may often be converted into fluorescent derivatives or decomposition products by applying different reagents. Hence, crude drugs are often assessed qualitatively in this way, and it is an important parameter for pharmacognostic evaluation of crude drugs [24, 25].