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