Ethnobotany studies the historical and present-day relationships between human societies and flora in the natural environment. The field focuses on the traditional uses of plants by native people who use their knowledge of flora in their habitat for food and for healing different ailments.
A prominent ethnobotanist who trailblazed the classification of plants in the Amazon rainforest during the 20th century was the American scientist Richard Evans Schultes. The Harvard educator was the first to scientifically study ayahuasca, a hallucinogenic drink largely derived from the vine of Banisteriopsis caapi and parts of other plants, such as Psychotria viridis and Diplopterys cabrerana, which trigger strong, yet brief hallucinogenic effects from the molecular compound N,N-dimethyltryptamine (DMT).
In a 2020 article authored by Merlin Sheldrake, the independent scholar wrote of an ongoing ‘enigma’ pervasive in the field of ethnobotany that Schultes, in his study of Amazonian hallucinogenic plants, failed to overcome. The ‘enigma’ is linked to some outstanding limits of ethnobotany regarding the accurate and proper classification of wild plants, Sheldrake argued. 
More specifically, a taxonomic “mismatch” exists between the observed indigenous plants and existing stable botanical identification data, wrote Sheldrake. One of Schultes’ students, for example, Homer Pinkleyevaluated plant samples shipped to him from the Amazon that were identified as being used in the making of ayahuasca.
“The plant material was sterile and could only be identified to the level of the genus, despite the fact that the Cashinahua and Culina people in southeastern Peru distinguished five or six varieties of the plant [at the site],” noted the Sheldrake article. Unable to precisely identify the plant material, Pinkley could not tell whether the local names matched scientific identifications, that is, a proper botanical understanding and identification of the species, or subspecies, in question. 
Schultes well understood this was a widespread problem for field experts.  In fact, in a paper published in 1986, Schultes referenced how native Amazonians could distinguish between five or six varieties of a vine used in making ayahuasca that he, the scientist, could not tell apart botanically.  The native Amazonian could “tell at once and frequently on sight and at a significant distance, without feeling, tasting, smelling, crushing, tearing or other physical manipulation, to which category a plant belongs”, Schultes reported.
Or as Sheldrake mentions, Schultes could not be “a credible reporter.” “Above all,” Sheldrake continues, “Schultes grappled with the unsettling clash between the cosmology of his Amazonian informants and that of his own modern science, a world view that prevented him from understanding the plants on the Amazonians’ own terms.”
Sheldrake urges that a degree of taxonomic stability is needed if ethnobotanists are to do their proper work, such as ascertaining that different classification systems are describing a specific plant in different ways. In certain cases, the same aspects of a plant are recognized by different taxonomic systems. However, one system may attach taxonomic meaning to a specific feature that another system does not even take into account. Therefore, how the plant is culturally represented and understood, is not wholly grasped by the entire field of scientists.
Schultes’ ‘enigma’ continues to plague the profession today.
 Sheldrake M. The ‘enigma’ of Richard Schultes, Amazonian hallucinogenic plants, and the limits of ethnobotany. Social Studies of Science. 2020;50(3):345-376. [journal impact factor = 3.885; times cited = 2]
 Pinkley HV. Plant admixtures to Ayahuasca, the South American hallucinogenic drink. Lloydia. 1969;32(3):305-314. [journal impact factor = 4.05; times cited = 7]
 Schultes RE. De plantis toxicariis e mundo novo tropicale commentationes X: New data on the malpighiaceous narcotics of South America. Botanical Museum Leaflets, Harvard University. 1972;23(3):137–147. [journal impact factor = N/A; times cited = 8]
 Schultes RE. Recognition of variability in wild plants by Indians of the Northwest Amazon: An enigma. Journal of Ethnobiology. 1986;6(2):229–238. [journal impact factor = 1.391; times cited = 10]