Genetic diversity among 13 northern populations of the declining coastal plant Eryngium maritimum L. at the northernmost extent of the species distribution range was studied using retro-transposon-based SSAP molecular markers. Diversity indices varied extensively among populations; some showing extremely low diversity whereas other populations exhibited moderate amounts of genetic variation. Differentiation among populations was highly variable as well. Interestingly, differentiation among northern populations was not influenced strongly by geographic distance. Closely situated populations were often more divergent than more distant populations suggesting other factors may be responsible for genetic structuring of E. maritimum populations. We propose that the following genetic and environmental factors combine together in a complex relationship to mould the present genetic structure of E. maritimum populations in this region: (1) historic biogeographical processes; (2) local environmental conditions at each site; (3) success of sexual reproduction and proportion of clonal propagation; (4) size of the population and influence of genetic drift; (5) level of fragmentation and isolation. Lastly, we suggest that the sustainable existence of Latvian populations is seriously threatened, unless recommended conservation measures are implemented.
