xi, 651 leaves : ill., plates ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1975) from the Dept. of Botany, University of Adelaide

In the UK, nearly half of the plants short listed for high conservation priority in the UK Biodiversity Action Plan are found in taxonomically complex groups. It is thought that a shift from species- to process-based conservation strategies, aimed at conserving the processes that generate diversity as opposed to simply the end product of these dynamic interactions, may benefit these groups. One group for which this strategy has been proposed is tetraploid Euphrasia. The underlying taxonomic complexity in this group is hypothesised to arise via breeding systems, hybridisation and local ecotypic adaptation. The goal of this thesis is to use morphological, ecological and molecular marker data to examine taxon limits and evolutionary processes in order to further understand the mechanisms involved in maintaining species boundaries and generating taxonomic complexity in tetraploid Euphrasia. This will not only make conservation in this group more effective, but will also provide a broader insight into some of the processes involved in plant speciation. A detailed study of two widespread, small flowered, tetraploid taxa, E. micrantha and E. scottica, showed that offspring are almost exclusively the result of self-fertilization. These taxa maintain distinctive morphologies, habitat preferences and chloroplast DNA variation throughout their range, suggesting that they represent coherent lineages within Scotland. As in other widespread inbreeding species, there are high levels of microsatellite differentiation among different populations of the same species. In northwest Scotland three complex populations of tetraploid Euphrasia were identified which comprised an array of many different morphs (recognised species, and putative hybrids). Analysis of chloroplast and microsatellite markers suggests that these different morphs represent distinct genetic groups. Within each site there is evidence both for habitat heterogeneity, and for association of morphs with this habitat variation. Intermediate morphs were not simple F1 hybrids, but are likely to have originated via hybridisation and subsequent selfing, surviving as independent recombinant lines, perhaps specialised for habitat types different from that of their progenitor parents. These stable morphs of hybrid origin could represent groups with adaptive potential that may result in the origin of a novel Euphrasia species. It will be important to further examine the processes involved in generating novel diversity in Euphrasia. For the time being, these complex populations must be recognised as sites requiring special protection within the context of a process-based conservation strategy.

Habitat fragmentation is one of the main threats to semi-natural grasslands all over Europe, causing reductions in both numbers of populations and numbers of individuals withinpopulations. Small isolated populations are particularly vulnerable to fluctuations that reducespopulation size and could lead to loss of genetic variation due to inbreeding depression, orfixation of harmful alleles due to genetic drift. The aim of this study was to investigate if thecritically endangered eyebright Euphrasia stricta var. suecica experiences pollen limitation,inbreeding depression and heterosis or outbreeding depression. Low pollen limitation waspredicted as well as low inbreeding depression due to high selfing rate. Outbreedingdepression or heterosis was expected based on previous studies indicating strong geneticdifferentiation among populations. This study was conducted in two traditionally managedmeadows in the central part of Gotland, Sweden, using supplemental hand-pollinations andcontrolled crosses. Individuals were collected when the flowering period was over and seedswere counted and weighed. There were no signs of either pollen limitation, inbreedingdepression, heterosis or outbreeding depression in any of the two wooded hay meadows. Thedegree of autonomous selfing was high, indicating that E. stricta var. suecica is not dependenton pollinators for seed production. A significant difference between the meadows was foundin proportion of viable seeds. As there were no signs of local adaptation, individuals could betranslocated between the two studied populations or seed sowings could be used to increasepopulation size. However, before such conservation efforts are undertaken, it is important toconduct further studies that investigate several populations including more life-stages.