THE COMPARATIVE David A. Baum2POLLINATION AND FLORALBIOLOGY OF BAOBABS(ADANSONIA-BOMBACACEAE)'ABSTRACT The baobabs comprise eight species with large, spectacular, nocturnal flowers. The African baobab, Adansoniadigitata, bas long been known to be bat-pollinated. In this paper I document the floral biology and pollination systemsof the remaining seven species. The two species in section Brevitubae, both endemic to Madagascar, are pollinatedby nocturnal mammals (fruit bats and lemurs). In contrast, the five species in section Longitubae, four endemic toMadagascar and one to Australia, are pollinated by long-tongued hawkmoths. In ail cases, animais besides the legitimatepollinators also exploited nectar and pollen. The two pollination systems occurring in the genus correlate closely withdifferences in the floral morphology, phenology, and nectar production. The baobabs comprise eight species in the genusAdansonia L. (Bombacaceae), six endemic to Mad-agascar, one to northwestern Australia, and oneoriginally from continental Africa that has beendispersed by humans elsewhere in the tropics(Wickens, 1983). They are tropical trees growingin savanna, deciduous forest, or, rarely, moist,semi-evergreen forest. The genus is characterizedby massive, often bottle-shaped trunks, palmatelycompound leaves, and a large, dry, indehiscentfruit containing reniform seeds embedded in anedible pulp. Ail species of Adansonia have large,spectacular flowers, but there are great differencesin their floral biology. This variation is partiallyreflected in the subgeneric classification, with thethree sections differing in the shape of the floralbud, orientation of the flower, and length of thestaminal tube (Hochreutiner, 1908; Baum, 1995).The African baobab (A. digitata L.) is the solerepresentative of section Adansonia. Two Mala-gasy species (A. grandidieri Baill. and A. suare-zensis H. Perr.) constitute section Brevitubae. TheAustralian species (A. gibbosa (A. Cunn.) Baumex Guymer) and four Malagasy species (A. rub-rostipa Jumm. & H. Perr., A. madagascariensisBaill., A. za Bail., and A. perrieri Capuron) con-stitute section Longitubae. In the early part of this century, African baobabsgrowing in botanical gardens in the Far East wereused to support the then heterodox assertion thattropical bats were important pollinators of sometropical plants. Van der Pijl (1934) inferred fromthe descriptions of van Harreveld-Lako (1926) thatA. digitata was bat-pollinated; this prediction was ' Fieldwork was funded by the National Geographic Society (4178-89 and 4615-91), the Roger Tory Peterson Institute, and the Madagascar Research and Conservation Program of the Missouri Botanical Garden, and was conducted under an accord between the Missouri Botanical Garden and the Government of the Democratic Republic of Madagascar. Fellowship support was provided by Washington University and the Missouri Botanical Garden. I thank the many governmental institutions in Madagascar and Australia and their staffs for logistical support. Logistical help was aiso provided in Madagascar by representatives of: CFPF-Morondava, COROI-Maromandia; Madagascar Research and Conservation Program, Missouri Botanical Garden; SAF-Morondava; and Worldwide Fund for Nature. This fieldwork would have been impossible without the assistance of many people in Madagascar and Australia. Inparticular I am indebted to Ruth Litovsky and Tricia Handasyde for their immense help in the field. The followingprovided useful advice and discussion: William Alverson, Patrick Armstrong, Tricia Handasyde, Peter Hoch, AllanLarson, Kevin Kenneally, Ruth Litovsky, Porter P. Lowry, David Mulcahy, Gabriela Mulcahy, Martin Nicol, PeterRaven, George Schatz, Kerry Shaw, Robert Sussman, Kenneth Sytsma, and Tim Willing, among many others. Ithank Helen Fortune Hopkins, Michael Grayum, and Michelle Zjhra for comments on early versions of this paper. I am grateful to H. Baker and the late I. Baker for analyzing nectar; E. Edwards, L. A. Nilsson, R. Walther, andL. Wasserthal for identifying hawkmoths; K. Dobat for identifying bats; and Kandis Elliott for preparing Figures 1,2, and 5-20. 2 Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166-0299, U.S.A. Current address: Departmentof Organismic and Evolutionary Biology, Harvard University, 22 Divinity Ave., Cambridge, Massachusetts 02138,U.S.A.ANN. MISSOURI BOT. GARD. 82: 322-348. 1995.