This thesis is concerned with speciation and population genetics in the plant genus Silene (section Elisanthe). The introductory chapter is a literature review covering characteristics of the species studied, and the current literature on their evolutionary dynamics and population genetics. The second and third chapters cover techniques used in all experiments, such as DNA extraction, sequencing and genotyping protocols, and explain the rationale behind the initial experimental design. The fourth chapter focuses on the multi-locus analysis of autosomal gene sequences from S. latifolia and S. dioica. The relationship between the two species was investigated using various analyses such as isolation modeling and admixture analysis providing estimates of evolutionary distance and extent of historical gene flow. The maintenance of the species despite frequent hybridization at present-day hybrid zones is discussed. The fifth chapter discusses S. diclinis, a rare endemic found only in Valencia, Spain. The nature of population structuring and the evolutionary history of this species were investigated using a multilocus approach incorporating individuals from S. diclinis populations. The causes of the restricted distribution and low population size of this species is discussed The concluding chapter discusses how the species evolved from a common ancestor amidst changing climatic and environmental conditions.

Crop wild relatives have been identified as ecologically and economically important plant genetic resources but are often a neglected resource. The recognition of the need for their specific conservation and their value for future use has been strengthened by the Convention on Biological Diversity and the International Treaty on Plant Genetic Resources for Food and Agriculture, both of which have been ratified by the UK. This thesis provides a detailed view of the ecological, geographic and genetic background to three crop wild relative species, Trifolium dubium, T. pratense and T. repens, of which the latter two are amongst some of the most economically important legume species in the UK. Assessments of ecogeography, amplified fragment polymorphism and single nucleotide polymorphism markers were employed to investigate the distribution of variation in these species across the UK, including outlying island sites. Based on this information it was possible to look for isolation by distance in populations in UK; identify areas containing unique variation; assess the conservation importance of island sites surrounding the UK and speculate on the causes of the observed patterns of diversity. Conservation recommendations were based on the cumulative data from this research to identify how the recommendations change with an increased focus on genetic diversity. These results provide insights into the use of different types of background information when setting conservation plans in widespread species, contributing to the development of conservation strategies for widespread species in general.