Anatomical and morphological variation in species and among populations of Opuntia in Southern Chihuahuan Desert [Variación anatómica y morfológica en especies y entre poblaciones de opuntia en la porciZapotitlánn sur del Desierto Chihuahuense]

Phenotypic variation in different populations of Opuntia cantabrigiensis, O. leucotricha, O. rastrera, O. robusta and O. streptacantha was evaluated by examining 28 anatomical and morphologic variables through discriminant analysis. These populations are separated from each other by distances ranging between 32 and 110 km. Altitude and annual average temperature showed no variation in the study area. Discriminant analysis separated populations of O. cantabrigiensis, which is the species having the lowest density (13 individuals ha-1), whilst some populations of other Opuntia species, whose densities were as high as 1,852 individuals ha-1, overlapped. No different ploidy levels were found among populations, although we recorded levels of ploidy between species that ranged from diploid (O. rastrera) to octoploid (O. streptacantha). Therefore, phenotypic differences between populations appear to be related to the density of individuals rather than to environmental variables, given the lack of environmental gradients or change in level ploidy