Medicinal keystone species: linking local medicinal systems and social-ecological systems in a One Health perspective.

Local medicinal systems, sometimes referred to as "traditional", are characterized by a strong integration between human, animal and ecosystem health, of which the rich interdependencies are central tenets of the One Health perspective. Drawing inspiration from the concept of cultural keystone species, developed over the last twenty years to deepen understanding of the importance of certain non-human species in local societies and the reciprocal relationships between them, we propose the concept of medicinal keystone species.They can be defined according to six criteria: (i) intensity, type, and diversity of medicinal use; (ii) naming and terminology within languages; (iii) role in narratives, ceremonies, or symbolism; (iv) persistence and memory of use despite changes in and threats to the medicine system; (v) Visibility and intelligibility of the foundations of a medicinal system; (vi) opportunities for resource acquisition from beyond local territories. Two examples are presented to illustrate the medicinal keystone species framework: (1) Quassia amara, a plant prominent in French Guianese Creole medicine, and (2) Castor canadensis, an animal central to medicinal systems of Algonquian Peoples of Eastern Canada.This concept may play an important role in the conservation of social-ecological systems. By identifying sets of resources that fulfil structural and functional roles in both local medicinal systems and the cultural identity of peoples and society, it helps recognize the medicinal knowledge systems of Indigenous Peoples and Local Communities (IPLC), including Afro-descendants, and emphasizes key components of their materia medica. In this way, it can support more effective access to local medicines in healthcare systems.