Medicinal plants

Medicinal plants

Most of the drugs which are still extracted from plants come from leaves, bark, roots or rhizomes. Leaves often become fragmented and detached; bark, roots or rhizomes can be difficult to identify from their macroscopic appearance. The proper authentication of crude drug material is essential for standards of safety and quality to be maintained. For these purposes, accurate anatomical and morphological descriptions of the drugs have been published. The legal standards are found in such volumes as the British and European Pharmacopoeias and the British Pharmaceutical Codex, and those of other countries. In these books, the style of morpho-logical and anatomical descriptions is very brief and to the point. Only those characters that will help to identify the material are given. Usually, these short monographs are carefully revised by a committee of experts. Herbal-ists are also aware of the need to have adequate control of the material they use, and work has been carried out to produce proper standards in reference works.

It is still often quicker to find out the identity of a crude drug (in the fragmented state) from its anatomy than from its chemistry. Importers of crude drugs are often experienced enough to know if they are buying pure material, or if adulterants are present. Sometimes samples will be sent for anatomical confirmation. For example Ipecacuanha, used in cough mix-ture can be adulterated with roots from alternative inferior species. Here microscopy can be used to give an indication of purity. The authentic source of the drug is Cephaelis ipecacuanha (Rubiaceae). Although rarely adulterated with other roots these days, there was a period when Ionidium (Violaceae) and other roots were regularly mixed in with the authentic material. Most of the adulterants have wide vessels in the xylem, whereas those in Cephaelis are narrow. The substitutes also lack characteristic starch granules, which are simple or, more usually, compound, with two or five or up to eight parts. The individual granules are oval, rounded or rounded and with one less curved facet, they rarely measure more than 15 µm in diameter. Sometimes Cephaelis acuminata is used as a substitute. This species is similar anatomi-cally, but has starch granules up to 22 µm in diameter.

Sometimes closely similar substitutes are put on the market when the usual source of material is unavailable, for example, when Bolivian Guarea bark is difficult to obtain, and a substitute from Haiti is available. Micro-scopic study has shown that the substitute is from a different species, be-cause the groups of phloem fibres are dissimilar but chemical tests prove it to be equally suitable for use. Occasionally the substitute may be poor and unsuitable. Rheum offi cinale root and rhizome is used medicinally, but Rheum rhaponticum is the vegetable. Fortunately, chemical and anatomicaltests can be applied to detect which species is present. Digitalis purpurea and D. lanata are used medicinally. They can be distinguished from one anotheron anatomical grounds, because the anticlinal walls of the abaxial epider-mal cells are more beaded inD. purpurea.

Herbal remedies used as folk medicines from tropical parts of the world are often only available in fragmentary form. Those wishing to determine the identity of such fragments need to use anatomical methods.