• We studied how the genetic structure helps in understanding the demographic history of a species and predicting its future, using the endangered orchid Spiranthes spiralis. • A Parisian population was mapped during three consecutive years. Its genetic structure was assessed using isozymes and compared with several populations from southern France. Seed dispersal distances were experimentally evaluated. Computer simulations were performed to reconstruct the population history. • Unlike southern France populations, the Parisian population exhibited two genetically distinct patches. Seed dispersal was limited to the neighbourhood of the fruiting plants. The simulations showed that the best explanation for the observed genetic structure was a recent colonization event by two small groups of founders. • Current patterns of gene flow should result in a rapid genetic and demographic homogenization. New populations of S. spiralis could be successfully established by few founders and exhibit significant growth rates without any detrimental effects of inbreeding. This offers insight into the successful management of endangered plant species in urban areas.
Keywords: Spiranthes spiralis; foundation; gene flow; genetic structure; inbreeding; population differentiation.