The doctrine of signature describes an ancient cognitive system relating the appearance, structure and characteristics of plants to symptom expressions of diseases in man-kind  . Such mirroring is understood to point from the potential medicinal curative, recognized in the plant by its exhibition of a similar expressions of signature as that seen in the symptoms of an illness . This concept is seen as drawing from the external, colour, structure etc. to conclude on the internal, the character and the healing action . Reference of this form of recognition, the doctrine of signature, is found in many historic writings from various places of the world. Therefore, such systemic resemblance has been viewed by many to be the origin of much of today’s herbal medicinal knowledge  .
In ancient times, the recognition of plants that were edible from those that were poison or in fact had healing potential, was a matter of experiential knowledge. At the time, many of a population were still largely unable to read or write, and learning was conducted by observation and oral tradition . Colour, smell, taste, structure, shape, and behaviour of plants were signs and symbols that revealed their uses   . Even the growth location of a plant could give hints to its healing potential .
There are various examples of signatures. The yellow of tumeric, or the blossoming flower of taraxacum (dandelion) may be seen as signalling the resemblance to bile, the bodily fluid excreted by the liver via the gallbladder. Remedies derived from both plants have been in use to treat ailments of the liver-gallbladder-pancreas system . The shape of a plants leaves, as for example in the the form of a heart as of Melissa officinalis, suggest it to be an effective remedy for weaknesses in this precise organ in the human body . The same holds true for Gingko bilboa, whose leaves have the shape of a human brain, and the tea of which is considered effective as a tonic in memory disorders .
The greatest proponent of the doctrine of signatures was Paracelsus (1493 – 1541) . He stressed, that man only had to observe and to use his senses in order to read in natures’ book . To him the doctrine of signature was not just restricted to the colour or shape of flowers, leaves, roots, bark or fruits, to him the consistency, the location, the properties of the soil in which the plant grew, the time and duration of bloom, too were signals of the characteristics and curative abilities of herbs and weeds . Paracelsus was convinced that “nature marks every plant that issues from her for what it is good” (p.257) .
Hahnemann, from his homeopathic perspective, opposed this theory , he insisted on the parallels of disease expression to pictures obtained of remedy substance that had been proven on a healthy subject. To him the illness producing substance trialled on the healthy individual acted as a healing agent, in energetic resonance with the disease affliction thereby producing a curative action  .
More recent research investigated the doctrine of signature and its relation to todays plant medicinal knowledge. Bennet  concludes in his critical appraisal of the doctrine that it was simply “a way of remembering and transmitting knowledge” and not “a means of discovery” (p.252) . To him there is no obvious relation of the signature of plants to their medicinal significance. Many plants that are used medically today have no such signatures, while many that do, have not been found to be of curative value. Yet an investigation into the modern-day usage of signature by Dafni and Lev  has found that in certain folk medical knowledge, the role of signature is still prevalent, even despite the advancements conventional medicine has brought.
The doctrine finds itself most widely used and applied today in anthroposophic medicine , but there acknowledges a further signatory resemblance, namely that of plants to planets . Unlike in Homeopathy, where ‘like cures like’ in the anthroposophic medical philosophy, the law of similars is opposed and medicines are selected according to “energetic patterns rather than homeopathic provings” (p.177) .
While in the scientific realm such resemblances and associations are still viewed critically and are refused, Richardson-Boedler  acknowledges , a form of resonance of the remedies of nature with “the psychological dynamic of a disease process” (p.27), and stresses, that immaterial levels are “yet largely elusive to the probes of science, but the concept of signature may facilitate “the understanding of the subjective, psychological and spiritual dimensions of nature and her beings” (p.28).
The doctrine of signature is therefore neither just myth, nor the sole origin of what we know of plant medicinal uses. It is a concept of old, a Genesis of health care led by experience and the need to remember and transmit knowledge. Either way it is a potential store of vast knowledge and wisdom that could still hold information on plant curatives that have not yet fully been investigated of the folk medical practices.
 Bennet, B. (2007) Doctrine of Signatures: An Explanation of medicinal plant discoveriy or dissemination of knowledge, Economic Botany, 61 (3), pp.246-255.
 Cornelius, P. (2002) Die Signaturenlehre, Natur und Heilen, 6, pp.25-31.
 Dafni, A. & Lev, E. (2002) The doctrine of signatures in present-day Israel, Economic Botany, 56 (4), pp.328-334.
 Junius, M. (1979) Spagyrics: The Alchemical Preparation of medicinal essences, tinctures and elixirs. Vermont: Healing Arts Press.
 Richardson-Boedler, C. (1999) The doctrine of signatures: a historical, philosophical and scientific view (I), British Homeopathic Journal, 88, pp.172-177.
 Richardson-Boedler, C. (1999) The doctrine of signatures: a historical, philosophical and scientific view (II), British Homeopathic Journal, 89, pp. 26-28.
 Personal lecture notes 1997.