Ethnobotanical study of medicinal plants traditionally used in the Arribes del Duero, western Spain. 
We studied traditional knowledge (TK) and current uses of medicinal plants among the inhabitants of the Arribes del Duero-ARD-(Spain), documenting traditional medical practices.  We interviewed 80 key informants (44 men and 36 women).  Their average age was 72 years (range 48-98 years).  We calculated the cultural importance for each species cited.  To analyze how TK varies with the characteristics of the different informants, we performed an ANCOVA, taking the number of use-reports (URs) provided by each informant as a variable to model, and age and gender as explanatory variables.  156 medicinal remedies were recorded; they were based on a single species and were cited by at least three independent informants, and half of them are still in use today.  These remedies are related to nine major organ systems and 54 therapeutic uses, and 70 species (belonging to 39 families) are used, most of which are herbs (64%).  The most relevant family is the Lamiaceae (23 remedies, 8 species) and the species employed in the greatest number of remedies (8) is Urtica dioica L. However, the taxon with the greatest cultural value is Hypericum perforatum L. (CI=0.71).  31% of the variability of the TK can be explained in terms of the age and gender of the informants (R(2)=0.315), the age factor having a positive effect.  Most of the remedies are related to the treatment of unimportant ailments, referring to disorders of the skin, and the respiratory and digestive systems.  The leaves and fruits are the most frequently sought plant parts (40 and 17% of the plants mentioned, respectively), and infusions (34%) and decoctions (28%) are the main methods used for preparing the remedies.  Likewise, we recorded remedies based on plant mixtures and ethnomedicinal novelties or rare uses, and comment on the influence exerted by superstition.  Currently, many people preserve a rich TK about medicinal plants, and it may be affirmed that the folk medicine is still very much alive in the ARD, above all as regards the treatment of certain common afflictions or unimportant ailments.