Agave turneri, a new species of Agave from the Sierras Cucapá and El Mayor in northeastern Baja California, Mexico, is a medium-sized species that does not produce offsets, has a relatively short and narrow panicle, and has a distinctive flower structure. The closest relatives to this new species are Agave moranii, which occurs approximately 200 km to the south of the type locality, and A. deserti var. simplex, which occurs in Arizona and California. This new species is a narrow endemic restricted to specific granodiorite and tonalite habitats in a hyperarid environment. Agave turneri appears to be a critically endangered owing to its habitat preference for specific types of granite in the Sierra Cucapá, threats due to prolonged drought and global change, and its close proximity to the Mexicali metropolitan area.