Aim of the study: Apart from empirically learned medicinal and pharmacological properties, the selection of medicinal plants is dependent on cognitive features, ecological factors and cultural history. In literate societies the transmission of medicinal plant knowledge through texts and, more recently, other media containing local as well as non-local knowledge has a more immediate and a more prolonged effect than oral transmission. Therefore, I try to visualize how field based studies in ethnobiology and especially medical ethnobotany and ethnopharmacology run the risk of repeating information and knowledge and illustrate the importance of differentiating and acknowledging the origin, transmission and rationale of plant use made by humans. Materials and methods: Reviewing literature dealing with the traditional parameters (e.g. hot/cold dichotomy, organoleptic properties, doctrine of signatures) influencing the selection and transmission of plant use in a juxtaposition to our recent finding of causal influence of text on local plant use. Discussing the passing down of knowledge by text as a special case of oblique/one-to-many knowledge transmission. Results: Historical texts on materia medica, popular books on plant use, clinical studies, and informants of ethnobotanical field studies generate a circle of information and knowledge, which progressively condi- tions the results of ethnobotanical field studies. While text reporting on phytotherapeutical trends may cause innovation through the introduction of “new” applications to local customs, persistently repeating well established folk remedies leads to the consolidation of such uses adding a conservative dimension to a local pharmacopoeia, which might not actually be there to that extent. Conclusions: Such a “shaping” of what might appear to be the results of a field investigation is clearly outside the ordinary principles of scientific enquiry. The traditional pillars of ethnobotanical field studies – that is, “input to drug discovery” and “conservation of cultural heritage” – are also incompatible with this process. Ethnobotancial field studies aimed at a contribution to natural products research and/or the conservation of cultural heritage, as well as those aimed at an assessment and validation of local pharmacopoeias should differentiate between local plant use and widespread as well as modern knowledge reported in popular textbooks and scientific literature.