Planta-nodriza interactions in Lophophora diffusa (Cactaceae) in a subtropial desert in Mexico

One of the two species from the genus Lophophora is the false peyote Lophophora diffusa, an endemic cactus species of the xerophytic shrubland at Queretaro, Mexico, considered threatened from illegal extraction due to its hallucinogenic and medicinal properties. We analyzed the spatial distribution of L. diffusa and its association with the locally dominant shrub species with the system SADIE (Spatial Analysis by Distance InclicEs). We also Studied the principal microclimatic factors (light, temperature, and humidity) beneath the canopy of the possible nurse plant species. The use of SADIE is a new approach to study the mechanisms of spatial distribution. Lophophora diffusa and the shrub species presented an aggregated distribution with patches and gaps, as indicated by the values of I-a = 4.179 for L. diffusa and I-a = 1.660 for the vegetation. Lophophora diffusa was positively associated with the arboreal vegetation, particularly with Larrea tridentata and Acacia sororia, but was negatively associated with Celtis pallida and Myrtillocactus geometrizans. Microclimate evaluation indicated that C pallida canopy significantly reduced radiation and temperature compared to the other species (L. tridentata, A.sororia y P laevigata). We had expected L. diffusa to exhibit a positive spatial association with C pallida; however, the reduction in light availability apparently limited seedling establishment of L. diffusa.