Old World plants in Andean healing, and the colonial survey that lets it be measured
The plant traffic between Spain and the Andes ran both ways. Surveys of the medicinal plants sold and used today in northern Peru and southern Ecuador find 17% of them to be Old World introductions, many carried in during the colonial centuries, and a bishop's eighteenth-century inventory is still the baseline against which two hundred years of change is counted. The same surveys record the cost: healers persecuted, and traditional medicine illegal in Ecuador until 1998.
Why this wins its question: The standard account of colonial botany in the Andes runs in one direction: cinchona, coca and quinoa leaving, knowledge extracted. That account is true and incomplete, and the correction is not an argument but a count - 17% of the medicinal plants in use today in the surveyed regions of northern Peru and southern Ecuador are Old World introductions, and a Spanish bishop's inventory is the instrument historians use to measure what has survived. This object states the count, names the survey it comes from, and puts the persecution of healers and the illegality of traditional medicine in Ecuador until 1998 in the claims rather than leaving them out - which is what makes the first half of the finding worth believing.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
The exchange in medicinal plants was not one-directional. A 2009 field study recording what is actually used and sold in northern Peru puts 510 taxa on record, of which "422 species (83%) were indigenous to Northern Peru, while 87 species (17%) were introductions".
Southern Ecuador shows the same proportion on a smaller list - 215 taxa recorded, of which "179 species (83%) were indigenous to Southern Ecuador, while 36 species (17%) were introductions" - and the same authors reported those counts for Loja province three years earlier, so the figure is stable across two of their surveys rather than a single result.
The introductions arrived with a purpose. Both studies state that many of the introduced species are medicinal plants brought in during colonial times for the treatment of European diseases, which is the unglamorous half of the Columbian exchange in remedies: the Andes supplied cinchona to the world, and Old World herbs entered Andean practice and stayed in it.
The living pharmacopoeia is not a relic. The 2009 study finds that "58% of the species sold in Peruvian markets and 41% of the species used in Ecuador were added to the pharmacopoeia within the last 200 years", so most of what is on the stalls today entered use after the colonial period ended, through continued experiment by healers and the public.
A Spanish colonial survey is what makes the change measurable. The eighteenth-century inventory compiled under Baltasar Jaime Martinez Companon, bishop of Trujillo, serves the modern authors as the baseline: they report that "only 41% of the species mentioned by Martinez Companon are still sold nowadays in Peru", that a further 32% are still used in the Amazon basin but no longer reach the coastal markets, and that 27% have completely disappeared from modern use. This corpus has not opened Martinez Companon's own volumes, whose repository is not reachable from this container, and cites the baseline through the modern study alone.
The cost belongs in the same paragraph as the transfer. The cited authors write that "traditional medicinal practitioners were immediately persecuted once the colonial administration took hold", that traditional medicine remained illegal in Ecuador until a constitutional change in 1998, and that "centuries of prohibition have led to a pronounced abandonment of traditional knowledge". The plants moved in both directions; the legal protection did not.
The two regions diverged, and the explanation offered is administrative rather than botanical. Northern Peru retains a strong healing tradition in which practitioners keep experimenting with new remedies, while much original plant knowledge in southern Ecuador has been lost; the authors attribute the difference to a more tolerant Peruvian administration and to Ecuadorian healers having had no comparable opportunity to experiment. That is their reading of a pattern in their own field data, offered here as such and not as an established finding.
The evidence base has a named limit. Both studies come from the same two researchers working the same northern Peruvian and southern Ecuadorian region, so the second corroborates the first without independently confirming it, and the percentages here describe what those surveys recorded in specific markets and communities rather than the Andes as a whole.