For purposes of research and international communication, the botanical identity of the plants used in medicine has also to be established accurately.

        Medicine functions in terms of chemical compounds and their interaction with the body. The distribution of identical chemical compounds in plants has several unpredictable and diverse patterns. While there are several compounds in a particular species, depending upon the therapeutic importance, one or a few compounds come to be considered important. Some compounds like the the flavonoids kaempferol, rutin, quercetin, etc., occur in a large number of diverse taxa. Some others may occur exclusively in one species, or several species of a genus, or different genera of a family or in very diverse and botanically unrelated taxa. Some examples are given here:

a) The opium alkaloids occur only in Papaver somniferum among over 100 species of the genus Papaver (Papaveraceae). Similarly cannabinoids occur only in Cannabis sativa (Cannabidaceae).

b) The alkaloids of Rauvolfia serpentina (Apocynaceae), are also present in varying quantities, in related Indian species such as Rauvolfia tetraphylla. Rauvolfia vomitora in West Africa, has more reserpine than Rauvolfia serpentina (Ayensu, 1986). Reserpine also occurs, though in small quantities, in Alstonia scholaris, of the same family.

c) The vinca alkaloids, vincristine (leucocristine) and vinblastine (vincaleucoblastine) occur in Catharanthus roseus (Apocynaceae), from Madagascar, now naturalised or cultivated in India and the Madagascaran endemic Catharanthus coriaceus (Ayensu, 1986).

d) The sweet saponin liquorice (glycyrrhizin) , occurs in roots of Glycyrrhiza glabra, the original classical source, and in Glycyrrhiza uralensis, both of which are exotic and are cultivated in northern India. The leaves of the Indian species, Abrus precatorius, of the same family (Fabaceae) as Glycyrrhiza, also contain liquorice, in greater quantities than in the species of Glycyrrhiza (Oliver-Bever, 1986; Kameswara Rao and Sangeetaa, 1993).

e) The anticancer alkaloid camptothecin occurs in the Chinese Camptotheca acumunata (Nyssaceae) and the very unrelated Indian species Nothopodytes foetida (Icacinaceae)

f) The alkaloid ephedrine, widely used in bronchial problems, was originally discovered in the species of the gymnosperm Ephedra, also occurs in the very far removed angiosperm species of the genus Sida (Malvaceae). This discovery was based on similar use of the two species in Ayurveda.

        These patterns of distribution would have been missed without correct botanical identities, which are essential not only to establish the original source, but also to make subsequent recollections of the plant material and to discover substitutes, if necessary.

        There are two ways of establishing the identity of medicinal plants from the classical sources.

        One is basing on the names and descriptions given in the source texts. The identification of the water weed and fern, Salvinia natans, was established by the descriptions in Charaka Samhitha and there was an error in this regard resulting in the use of a wrong species earlier (Professor B A Hegde, Kolhapur, personal communiation). The risk of misunderstanding the descriptions is of a major concern in this method.

       The second method is to obtain a sample of the plant material from reliable and authentic users and to establish its botanical identity. The basis is continued traditional identification and use. An age old misinterpretation or a substitute being used in the original name for a long time due to the paucity of the original material or out of ignorance, are the risks in this approach, besides the problem of determination of who or what is an authentic source. Many competent sources are very secretive, blocking the process.

        Repeated verification and reconfirmation are the safer means of establishing plant identities. Botanical identities should be established based on complete specimens and whole plants and just not the part which is the source of the drug such as the roots, leaves, bark, fruits or seeds. By and large the identities have been verified for a large number of medicinal plants (Vaidya, 1982; Sivarajan and Balachandran, 1994), yet several problems persist, a few of which are given here:

a) The identity of brahmi is a long standing controversy. The confusion is between Centella asiatica (Apiaceae) and Bacopa monnieri (Scrophulariaceae), which are botanically unrelated,. Both the species prefer wet soils and in both, the active principles are saponins, though qualitatively different. They are used for various purposes, more importantly as memory enhancers. Another name Hydrocotyl asiatica also appears in literature, which is now understood as a synonym of Centella asiatica. It is generally agreed that Centella asiatica is brahmi as used in south India and Bacopa monnieri is mandukabrahmi, more popular in the north India. Nevertheless, doubts are raised now and then.

b) Another infamous example of a deep rooted mistaken identity is the ashoka tree, whose bark is an important ingredient in the formulations, such as ashokarishta, used to treat menstrual problems. The correct identification is Saraca asoca (=Saraca indica, Caesalpiniaceae) but a very large number of people erroneously consider the unrelated Polyalthia longifolia (Annonaceae) as the ashoka tree. In consequence, the wrong plant is used either out of ignorance or even deliberately as a cheaper, though an irrelevant, substitute. The therapeutic consequences are any body’s guess.