Genetic diversity in three genera of perennial plants found in the sand pine, oak scrub in peninsular Florida was examined by allozyme electrophoresis. These plants vary greatly in terms of geographic range, population size, pollination ecology, and seed dispersal mechanisms. Ceratiola ericoides (Empetraceae) is a shrub that occurs throughout scrub and other sandy habitats in Florida and neighboring states. In contrast, Eryngium cuneifolium (Apiaceae) is a Federally endangered herbaceous perennial, limited to the southern end of the Lake Wales Ridge, site of a proposed National Wildlife Refuge that would be the first designed primarily to protect plant diversity. Four species of endangered woody perennial Dicerandra (Labiatae) are pan of a monophyletic group endemic to Florida sand pine scrubs; Dicerandrafrutescens and D. christmanii are found on the southern end of the Lake Wales ridge, D. cornutissima is found in north-central Florida, and D. immaculata occurs in a small area along Florida's Atlantic coast. Allozyme electrophoresis of 17 loci for C. ericoides indicated that 64.7% of the loci were polymorphic (Ps), that there were 2.55 alleles per polymorphic locus (APs), and that the mean gene diversity (Hes) was 0.141. The proportion of genetic diversity among the four populations (GST) was 0.059. For the 31 loci analyzed in E. cuneifolium, Ps was 32.3%, APs was 2.1. and Hes was 0.104. GST was 0.106. The woody Dicerandra species complex (four species) was analyzed for 17 loci. Ps was 64.7%. APs was 3.1, and mean gene diversity was 0.219. The mean GST value across the species complex was 0.137. Taken together these results suggest that considerable genetic variation is still present in the relict populations of the rare scrub taxa (Eryngium and Dicerandra), but that to preserve current levels of genetic variation will require protecting areas in each of several different scrub regions along a 350-km stretch of peninsular Florida.
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