Walker, J. L. and A. M. Silletti (USDA Forest Service, Southern Research Station, 233 Lehotsky Hall, Clemson University, Clemson, SC 29634). A three-year demographic study of Harper's Beauty (Harperocallis flava McDaniel), an endangered Florida endemic. J. Torrey Bot. Soc. 132: 551–560. 2005.—Harperocallis flava is a federally listed endangered plant narrowly endemic to the Florida panhandle. A lack of knowledge about Harperocallis population dynamics currently hinders conservation planning. Our objectives included describing ramet size, reproductive status, and mortality and recruitment rates in natural populations of H. flava. In 1998, we established permanent plots and marked individual ramets at six sites representing two habitat types in Apalachicola National Forest. At each site, we established ≥ 3 plots of varying size (0.12–1.8 m²) to include ∼300 ramets / site. In the first year we tagged, recorded reproductive status of, and measured individual ramets (# of leaves, longest leaf length). In 1999 and 2000, new ramets were tagged and all tagged ramets were re-measured. Analysis of variance methods were used to detect site, year, and habitat effects on response variables. Total number of ramets sampled varied between sites and declined from year to year. The proportion of ramets bearing reproductive structures was low (0.01 to 0.10) and varied with site and year. Logistic regression indicated that larger ramets were more likely to produce reproductive structures, and that smaller ramets suffered higher mortality. There were significant habitat and year effects on mortality; recruitment differed between years. The relatively short duration of this study precluded examination of potentially important fire effects. A rhizomatous habit and unexpected levels of crayfish-induced mortality suggest that knowledge of population structure and processes at larger scales is needed to develop effective monitoring and management strategies for H. flava.