POLLINATION BIOLOGY OF 2 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 columna r cacti. These two species form mixed forests in the western Tehuacan Valley, Mexico. The flowers of both N. mezcalaensis and N. macrocephal a exhibit nocturnal anthesis, are self-incompatible, and are pollinate d primarily by three species of nectar-feeding bats (Choeronycteris me xicana, Leptonycteris curasoae, and Leptonycteris nivalis). Neobuxbaum ia mezcalaensis is androdioecious, a breeding system that appears to b e uncommon among Cactaceae. Neobuxbaumia macrocephala is hermaphroditi c. we hypothesize that columnar cacti show a geographical dichotomy in floral biology specialization that probably can be related to predict ability in pollinator abundance.