Abstract
BackgroundMost reports of domesticated plants that involve a domestication gradient or inter-specific hybridization in Mexico have focused on those used as food. This study provides knowledge about these processes in two aromatic medicinal plants, Agastache mexicana (Lamiaceae) and A. m. subsp. xolocotziana, widely used in Mexican traditional medicine for the treatment of gastrointestinal ailments and for their sedative effect. Different populations of A. mexicana along a gradient of domestication are found in the foothills of the Popocatepetl volcano of central Mexico, while in this same area the subsp. xolocotziana grows only in the cultivation, possibly a product of hybridization between A. mexicana and Agastache palmeri. This study links ethnobotanical, morpho-physiological, and phytochemical evidence to document the domestication of both taxa as well as elucidates the possible hybrid origin of the subsp. xolocotziana.MethodWe analyze three groups of data derived from (1) 80 semi-structured interviews aimed at documenting the selection criteria related to the use and management of A. mexicana; (2) a cultivation experiment under homogeneous conditions, evaluating 21 floral, vegetative, and seed characters (that were important according to ethnobotanical information) in 97 plants corresponding to 13 populations of the taxa under study; and (3) the chemical profiles of the essential oils of these plants by means of a thin-layer chromatography.ResultsBy linking the three types of evidence, two evolutionary processes are distinguished: (1) A. mexicana occurs in the encouraged-cultivated phases of the domestication gradient and (2) A. m. subsp. xolocotziana may have originated through inbreeding depression or hybridization. These two cultivated plants show a domestication syndrome based upon organoleptic differentiation due to their dissimilar phytochemical composition and gigantism in flowers, seeds, and rhizomes (the last enhancing their asexual reproductive capacity). In addition to this, A. mexicana exhibits more intense floral pigmentation and foliar gigantism while subsp. xolocotziana presents floral albinism and partial seed sterility.ConclusionTwo divergent evolutionary processes are reported for the domestication of A. mexicana as a result of the intensification of its use and management. The selection processes of these plants have resulted in alternation of the organoleptic properties based upon the divergence of the phytochemical composition. Also, gigantism has been selected in culturally preferred plant parts and in correlated structures. The preceding characteristics reinforce the joint use of these plants in infusion in Mexican traditionalmedicine for the treatment of gastrointestinal diseases and for their sedative effects.
Highlights
Most reports of domesticated plants that involve a domestication gradient or inter-specific hybridization in Mexico have focused on those used as food
The first written mention of A. mexicana occurred in the sixteenth century (1552) when it was registered in Libellus de medicinalibus indorum herbis, one of the oldest manuscripts of Mexican medicinal plants, under the Nahuatl name of tlalahuehuetl; its sap was applied to wounds [34,35,36]
Ethnobotanical evidence Use The 80% of the people interviewed mention that the infusion combining A. mexicana and the subsp. xolocotziana is drunk to treat principally (75%) gastrointestinal, menstrual, and nerve pains as well as to combat “coraje” and secondarily (60%) in cases of “susto” or “espanto” [39]
Summary
Most reports of domesticated plants that involve a domestication gradient or inter-specific hybridization in Mexico have focused on those used as food. Different populations of A. mexicana along a gradient of domestication are found in the foothills of the Popocatepetl volcano of central Mexico, while in this same area the subsp. Xolocotziana grows only in the cultivation, possibly a product of hybridization between A. mexicana and Agastache palmeri. The domesticated plants have a greater fitness under cultivation and are propagated from vegetative parts, seeds, and/or transplants of complete individuals. The common suite of differential characteristics between cultivated domesticates and their ancestors (wild, tolerated, encouraged, or parental in the case of hybridization) is known as domestication syndrome, which includes gigantism in used parts and correlated structures, indicating its evolutionary process under domestication [1, 12]
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