This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
The study of botany is neglected in our medical colleges; so it is too often forgotten that plants are just as definitely related to each other as are inorganic chemical compounds. Credulity, as involves botanic remedies, is proportional to ignorance of botanical relationships. We may in our neighborhood know the Smith family and their strong points and limitations. Hence, when any one of the Smiths lays claim to ability and characteristics foreign to the family in general, we indulge our doubts until after he proves out in his claims. Botanically we may know the Labiatae as mints and non-poisonous aromatics. We may look up this order of plants in a work on botany and note that forty-five species of them are indigenous to the United States, Thymus vulgaris being the most active one. And yet hedge hyssop, of this order, has recently been exploited as one ingredient of a remedy for cancer. Knowing the Labiatae, how improbable is it that any member of the order would, or could, have any influence upon the course of so serious a disease!
On the other hand, when echinacea is exploited as a remedy by many physicians, some claiming much for it, and others - those opposed - wholly condemning the plant as inert, it need be no stranger to us, for we know its natural order, the Compositae. So we look up the Compositae and find that one-tenth of all the flowering plants of the world are of this order and few of them poisonous, the exceptions being Liatris odoratissima, used in smoking tobacco, and producing cerebral intoxication; tansy, which has occasionally caused death; Artemisia absinthium, the toxic agent of absinthe, which the French Government has found necessary to suppress; and perhaps a few more. Others of the order, while not actively toxic, are possessed of definite activity. We may note lactucarium, eupatorium, erigeron, grindelia, matricaria, and taraxacum.
So, then, there is at least some ground for us to expect that echinacea may be one of the exceptional plants among the Compositae, although we would not expect, from its botanical relationship, that it may be either markedly toxic or quick acting, since none of the poisonous Compositae are rapid in toxic effect.
The natural order Solanaceae, or night-shades, we know are narcotics; hence we would expect to find any one of this order an active drug.
The deduction from all this is: While the plants of the natural order Labiatae might be useful, we would not expect to find active drugs among them; among the Compositae we would expect to find a few agents of toxic or energetic character, while among the Solanaceae we would expect energetic narcotics. Throughout the whole botanical classification we find this rule to be of value in forming some estimate of the probable activity of a botanic drug.
But academic considerations do not always rule in this practical world. Drugs are not selected purely on the basis of their toxicity, since many non-toxic ones are exceedingly useful. There is easily selected a list of botanic drugs of worldwide recognition. The following are recognized in from sixteen to nineteen pharmacopeias. I have arranged them according to botanical order. Note how our academic rule is at sixes and sevens with the practical matter of fact.