Aborted fruits of Opuntia microdasys (Cactaceae): insurance against reproductive failure.

New individuals in clonal populations arise through the recruitment of sexual or clonal offspring. The predominance of one type of regeneration over the other has been correlated with different selective environmental pressures. We compared the reproductive mode (sexual through seeds and vegetative through plantlets or detached cladodes) of Opuntia microdasys from three desert habitats of the Chihuahuan Desert: bajada (BH), hill-piedmont (HPH), and an interdune (IDH). Successful establishment and growth of plantlets were determined in two experiments: (1) the effect of light (three levels of photosynthetically active radiation [PAR]: full, low, and medium) and two levels of watering and (2) maternal effects and provenance of plantlets. Adult plant densities did not differ among habitats (639 individuals/ha), but the number of offspring and fruit production increased significantly at BH. Plantlets (94.3%) dominated the form of recruitment for all habitats, followed by cladodes (3.1%) and seedlings (2.6%). A higher proportion of plantlets established in the low and medium PAR treatments (76%) in comparison to full exposure (39%). Maternal factors affected survival and growth, but plantlet provenance did not. The high fruit abortion rate resulting from environmental and maternal effects provided suitable conditions for establishment of plantlets.