Geographical Variation in the Widespread Temperate Epiphyte, Epidendrum magnoliae Muhlenberg (Orchidaceae)

Abstract

Epidendrum magnoliae is a widespread epiphytic orchid that occurs in Mexico and the United States. We investigated patterns of genetic divergence among populations of E. magnoliae distributed from North Carolina to south-central Florida. We found that populations of E. magnoliae maintain a high level of genetic diversity, 89.5% of the total variation within the species, while genetic diversity among populations was only 10.5%. Extensive gene flow has occurred within and among the northern and southern sampled regions of E. magnoliae. However there was also a significant relationship between genetic and physical distance, indicating that gene flow is reduced between more distantly spaced populations. The three populations sampled at the extreme ends of the species distribution in the United States were less diverse than more centrally located populations, suggesting a reduced rate of immigration and an increase in genetic drift. It has recently been proposed that speciation in orchids is likely due to the rapid and combined effects of genetic drift and sporadic selection. Such a scenario is more likely to occur in peripheral populations like those of E. magnoliae.