Pollination biology of two columnar Cacti (Neobuxbaumia mezcalaensis and Neobuxbaumia macrocephala) in the Tehuacan Valley, central Mexico

We document the pollination biology and mating systems of Neobuxbaumia mezcalaensisand Neobuxbaumia macrocephala, two Mexican giant columnar cacti. These two species form mixed forests in the western Tehuacan Valley, Mexico. The flowers of both N. mezcalaensisand N. macrocephalaexhibit nocturnal anthesis, are self-incompatible, and are pollinated primarily by three species of nectar-feeding bats (Choeronycteris mexicana, Leptonycteris curasoae,and Leptonycteris nivalis). Neobuxbaumia mezcalaensisis androdioecious, a breeding system that appears to be uncommon among Cactaceae. Neobuxbaumia macrocephalais hermaphroditic. We hypothesize that columnar cacti show a geographical dichotomy in floral biology specialization that probably can be related to predictability in pollinator abundance.