The long-term stability of orally transmitted ethnopharmacopoeias is of interest, but difficult to study for lack of information on plants used by a specific past culture. Similarities between modern Italian ethnopharmacopoeias and Dioscorides' classical text have been proposed to derive from modern replacement of traditional practices with those from published translations of Dioscorides. Ibn al-Baytar produced the best compendium of medicinal substances in medieval Islamic science. He gave "Berber" common names for some plants, which were presumptively used by North African Amazigh people. Since Amazigh traditional knowledge was largely transmitted orally, with little access to medieval literature, this allows comparison of historic (>
750 years ago) practices and modern practices that are unlikely to be causally derived. Presumptive identities for Ibn al-Baytar's plants with Berber names were obtained from key references. Recent ethnomedicinal publications from Amazigh-populated areas in North Africa were surveyed for reports of those species and homologous common names. Of 46 historically used plants, an estimated 60.9% are still used in Amazigh regions, 78.6% with homologous common names. This is likely to underestimate persistence of species use across the entire local pharmacopoeia. Second, emulating a published analysis of Dioscorides, plants reported by three large recent studies in Amazigh regions were compared with plants recorded by Ibn al-Baytar and in a comprehensive modern Moroccan reference. Between 58.2% and 73.8% of species included in individual studies were recorded by Ibn al-Baytar
of the 46 shared among all three, 82.6% were recorded by Ibn al-Baytar and 100% by the modern reference. An historical compilation may be more likely to mention plants that are widely used today simply because a thorough author could document most plants that were widely used at the time
use of such data to assess causality should take that effect into consideration.