Reproductive Biology and Conservation of the Living Rock Ariocarpus fissuratus

The globose cactus Ariocarpus fissuratus, known as “living rock,” is renowned for the singular morphology of its extremely cryptic single stem/taproot, which results in a resemblance of their tubercles to rocky soil. Their beauty has placed Ariocarpus among the top rated illegally traded cactus. In the Cuatro Cienegas Basin, important populations of A. fissuratus occur. This is the only Ariocarpus out of seven species in the genus, found outside Mexico, reaching southern Texas. In order to determine the influence of sexual reproduction to the conservation of healthy populations, we studied the reproductive ecology of A. fissuratus including floral morphology and phenology, interaction with insects, and mating and breeding systems. Results indicate that floral phenology is remarkably synchronic, and it occurs from middle October to early November through a few pulses that vary in onset and duration but lasting only 5 or less days. Genders are separated within the flowers in time and space, diminishing the probability of selfing. Numerous pollen grains and nectar are produced as rewards for pollinators, a feature that suggests a xenogamous system. A. fissuratus is an outcrosser, as indicated by forced pollination treatments. Floral visitors include bees, wasps, flies, butterflies, and beetles; only solitary bees behave as pollinators. Species assemblage of bee pollinators vary between years, suggesting that functional specialization of pollinators occurs in this species. In addition, we observed a high incidence of florivory by a tenebrionid beetle. We conclude that success of sexual reproduction is critical for the conservation of this cactus, but its short flowering phenology, its outcrossing mating system and dependence on pollinators, exotic floral visitors (the possible negative effects of A. mellifera), and florivory may be caveats to the maintenance of healthy populations in this species.