Ceratozamia zaragozae Medellín-Leal (Zamiaceae), an endangered Mexican cycad: New information on population structure and spatial distribution

Abstract

Ceratozamia zaragozae has been considered to be the most threatened cycad species in its genus since only 50 individuals were reported for the only known population in the state of San Luis Potosi, Mexico. In this report we present information on newly discovered populations, as well as data on their population structure and spatial distribution. Six different populations were found, one of which is located in a Natural Protected Area. Population density was low (0.05 ± 0.038 ind/m2) and populations exhibited an unconventional ecological affinity for the genus, occurring on igneous soils in oak and pine-oak forests at elevations over 2000 m. Populations showed heterogeneous growth rates (λ = 0.89 ± 0.49). Spatial clustering patterns in all populations indicated adequate recruitment, low survival of juveniles, and spatial dependence between seedlings/juveniles and reproductive adults. We recommend the ex-situ cultivation of the species and the establishment of corridors between areas of habitat, in order to secure the preservation of the species.