The doctrine of signatures – does the appearance of plants explain their healing powers?

Art in Dutch: AS Nijhuis-Bouma and AGM van Asseldonk; Journalistic review, 9 references.
Ned Tijds Fytoth 2018 (31) nr 1: pag 9-11.  ABSTRACT: 

This article  EB Ass & N-B DOS 2018 1-9-11   adresses the definition, historical development in Europe and provides some examples of the ‘doctrine of signatures’ (DOS).

The DOS assumes a relationship between certain anatomical and physiological plant characteristics (for example leaf shape, colour of plant juice, smell) and its medicinal effects.
Quite often it is combined with the religious belief that God placed these signs there for humans to discover. The history of herbal manuscripts and printed herbals, from antiquity to present times, shows many plants that are presented as examples of the DOS. At the same time, authors from all these eras warn against using the DOS as an indication for herbal practice. Ethnobotany professor Bennett calls the DOS just a mnemonic aid (i.e. something that will help you remember things that are difficult to learn by heart). Scientists however doubt if the DOS has ever given rise to significant medicinal plant knowledge.

Well-known plant examples that are often attributed to this DOS are lungwort (Pulmonaria officinalis) with its characteristic white spots on the leaves, resembling the lungs of tuberculosis patients; the wallnut (Juglans regia) because the inside seems to resemble the human cerebellum; the eyebright flower (Euphrasia stricta) that looks like an inflamed eye; the yellow stem juice of celandine (Chelidonium majus) that has the appearance of bile, and the red coloured oil in the yellow flowers of Saint John’s wort (Hypericum perforatum) that refers to its use on bleeding wounds.

Nowadays the DOS philosophy has again become popular amongst some herbalists that want to apply a more holistic or spiritual approach to selecting patient-specific plant remedies.
But it is very important to always let proper scientific experience in medical practice and toxicology be the major guide here. Applying the DOS can pose severe risks when it concerns potentially dangerous plants such as 
Aristolochia spp. The flowers of these plants are uterus-shaped, the name means ”good lochiaand the plant has been used for delivery problems. However, current knowledge tells us that this plant is far too toxic for internal use.

Therefore, the DOS should only be considered as a historically interesting, but outdated theory from an ancient period when magic, mythology and religion played very important roles.