204 Journal of the Torrey Botanical Society 132(2), 2005, pp. 204–213 Outcrossing effects on the reproductive performance of Hypericum cumulicola, an endangered Florida scrub endemic 1 Matthew D. Trager 2,3 Department of Wildlife Ecology and Conservation, PO Box 110430, University of Florida, Gainesville, FL 32611 Eric S. Menges Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862 Pedro F. Quintana-Ascencio Department of Biology, University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816 Carl W. Weekley Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862 TRAGER, M. D. (Dept. of Wildlife Ecology and Conservation, University of Florida, Gainesville, FL 32601), E. S. MENGES (Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862), P. F. QUINTANA-ASCENCIO (Dept. of Biology, University of Central Florida, Orlando, FL 32816), AND C. W. WEEKLEY (Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862). Outcrossing effects on the reproductive performance of Hyper- icum cumulicola, an endangered Florida scrub endemic. J. Torrey Bot. Soc. 132: 204–213. 2005.—We investi- gated the effects of self-fertilizing and within-population outcrossing in two populations of Hypericum cumuli- cola, a perennial herb endemic to xeric scrub habitats on central Florida’s Lake Wales Ridge. To examine the relationship between pollen source and reproductive performance, we compared fruit set, seed set, percent germination and net fertility (mean number of seedlings produced per flower within a pollination treatment) of hand-pollinated selfed and outcrossed flowers. There were no significant effects of categorical pollen source (self, near outcross, far outcross) on fruit set, and logistic regression showed no effect of interplant distance. Overall and at one of the two populations, far outcrosses had higher seed set than selfs and we found a weak but significant positive correlation between outcrossing distance and seed set. Percent seed germination was unaffected by pollen source. Net fertility was significantly correlated with outcrossing distance overall and at one of the two sites. These results show that pollen source may influence reproductive performance in Hypericum cumulicola, but the effects are fairly weak and inconsistent among populations, suggesting that outcrossing distance is not an important factor affecting small-scale population dynamics of this species. Key words: Florida scrub, Hypericum cumulicola, inbreeding, Lake Wales Ridge, mating system, outcrossing. Plant species with restricted geographic rang- es and small population sizes tend to have rel- atively low genetic diversity and high rates of biparental inbreeding (Karron 1987, Keller and Waller 2002). Consequently, crosses between genetically related parents may produce fewer or 1 Funding for this project was provided by the Na- tional Science Foundation (DEB 98-15370) and Arch- bold Biological Station. 2 We thank the Florida Department of Environmen- tal Protection and the Florida Fish and Wildlife Con- servation Commission for permission to conduct re- search at Lake June in Winter State Park and the Lake Placid Scrub Preserve, respectively. We also thank Marinela Capanu, Barbara Stimpson, Darien Mc- Elwain, Amanda Brothers and Jennifer Shafer for as- sistance with various aspects of this study. 3 Author for correspondence, E-mail: mtrager@ufl. edu Received for publication April 10, 2004, and in re- vised form November 12, 2004. less fit offspring due to prezygotic factors or poor postzygotic performance (Sobrevila 1988, Montalvo 1992, Byers 1995, Keller and Waller 2002, Souto et al. 2002). Although genetic purg- ing may reduce the potential negative effects of inbreeding (Husband and Schemske 1996, Byers and Waller 1999), many small and genetically depauperate populations nevertheless face great- er risk of extinction from environmental and de- mographic stochasticity (Shaffer 1987, Tanaka 2000, Dennis 2002). As such, examining the ef- fects of inbreeding in natural populations may have important implications for protecting pop- ulation health and conserving genetic diversity of many rare plant species (Hamrick et al. 1991, Ellstrand and Elam 1993, Byers 1998, Keller and Waller 2002, Paschke et al. 2002). Even among self-compatible plant species, outcrossing within and among populations often improves reproductive performance. Outcross-