Extensive monovarietal cultivation of Agave tequilana Weber var. azul is threatening the diversity of the germplasm used in traditional Agave spirits production in west-central Mexico. To promote the preservation, use, and management of this germplasm, an ethnobotanical and morphological study was done in the center and south of the state of Jalisco, Mexico. The richness, distribution, and morphological variation of wild and cultivated Agave populations were characterized, and producers' roles in germplasm maintenance and diversification were analyzed. Results indicated that: 1) A. angustifolia and A. rhodacantha are the primary gene pools used for selection; 2) Traditional landraces are differentiated morphological entities; and 3) In situ maintenance and increase of Agave germplasm diversity are the result of constant selection of wild germplasm, producer management of populations in the wild-domesticated gradient, and preservation of old landraces. Preservation of Agave germplasm diversity in west-central Mexico requires increased cultivation and valuation of traditional landraces.