Genetic diversity within a threatened, endemic North American species, Euphorbia telephioides (Euphorbiaceae)

The southeastern United States and Florida support an unusually large number of endemic plant species, many of which are threatened by anthropogenic habitat disturbance. As conservation measures are undertaken and recovery plans designed, a factor that must be taken into consideration is the genetic composition of the species of concern. Here we describe the levels, and partitioning, of genetic diversity in 17 populations of the rare and threatened Florida endemic, Euphorbia telephioides (telephus spurge). Species-wide genetic diversity was high (Ps = 91%, APs = 3.81, As = 3.57 and Hes = 0.352) as was mean population genetic diversity (Pp = 81%, APp = 2.98, Ap = 2.59 and Hep = 0.320) which ranks it among the highest 10% of plant species surveyed. Partitioning of genetic variation (Gst = 0.106) was low compared to other herbaceous outcrossing perennials indicating high historical gene flow across its limited geographic range. Among population Gst values within the three Florida counties in which it occurs, Gulf (0.084), Franklin (0.059) and Bay Counties (0.033), were also quite low. Peripheral populations did not generally have reduced genetic variation although there was significant isolation by distance. Rarefaction analysis showed a non-significant relationship between allelic richness and actual population sizes. Our data suggest that E. telephioides populations were probably more continuously distributed in Bay, Gulf and Franklin Counties and that their relative contemporary isolation is a recent phenomenon. These results are important for developing a recovery plan for this species.