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Members of Zygophylloideae are shrubs, shrublets and herbs of arid and semiarid areas of almost all continents, and many of the species are major components of the vegetation in their areas of distribution. A phylogenetic analysis of Zygophylloideae based on noncoding trnL plastid DNA sequences and morphological data, indicates that the currently recognised genera Augea, Tetraena, and Fagonia, are embedded in Zygophyllum. A new generic classification based on six monophyletic and morphologically distinctive entities is proposed here: Augea, Fagonia, Melocarpum, Roepera, Tetraena and Zygophyllum.

The taxonomy of the genus Fagonia is revised in detail. A key to the 34 species recognised is presented, as well as descriptions and distribution maps for each species. Five new species are described and illustrated, F. densispina, F. gypsophila and F. latistipulata from Somalia, and F. hadramautica and F. mahrana from the southern part of the Arabian peninsula. Of the accepted species, 26 are restricted to the Old World and eight to the New World. The names of all four species of Fagonia currently on the IUCN Red List of Threatened Plants are put into synonymy. Instead, eight other species are proposed for this list.

Relationships within Fagonia are inferred from analysis of plastid trnL intron and nuclear ribosomal ITS sequences. The phylogenetic analysis is performed using parsimony and Bayesian model averaging. All species of Fagonia in the Old World, except F. cretica, form a weakly supported clade, and all Fagonia species of the New World, except F. scoparia, form a second, well supported clade, sister to the Old World clade. Fagonia scoparia, endemic to northeastern Mexico, is sister to all other Fagonia species. Vicariance-dispersal analysis indicated that the occurrences of Fagonia in South America and southern Africa are due to dispersals, and that the ancestor of Fagonia had a distribution in agreement with the boreotropics hypothesis.

To investigate possible congruencies between DNA sequence data and secondary chemistry, we compared nuclear ribosomal DNA (nrDNA) sequence data, sesquiterpene lactone (STL) contents, and cytometric data from 35 accessions of 16 Arnica (Asteraceae) species and two outgroup taxa (Layia hieracioides and Madia sativa), using phylogenetic inference and principal component analysis (PCA). Several groups supporting multiple accessions of the same species (of A. montana, A. longifolia, A. gracilis, and A. chamissonis) are congruent between the phylogenetic trees based on nrDNA and STL data. Sesquiterpene lactone profiles were found to be highly consistent within multiple samples of A. montana and A. longifolia respectively. Moreover, sesquiterpene lactone data support subspecies classifications of A. chamissonis and A. parryi, with additional support from DNA sequence data and cytometric data. Morphology, STL data (PCA), cytometric data and DNA sequence data suggest a hybrid origin of one accession (A. gracilis × longifolia). In A. gracilis, A. latifolia, and Layia hieracioides, previously not investigated for STLs, we found large amounts of xanthalongin derivatives. This is the first time STLs have been reported from subtribe Madiinae.

Many empirical studies have revealed considerable differences between nonparametric bootstrapping and Bayesian posterior probabilities in terms of the support values for branches, despite claimed predictions about their approximate equivalence. We investigated this problem by simulating data, which were then analyzed by maximum likelihood bootstrapping and Bayesian phylogenetic analysis using identical models and reoptimization of parameter values. We show that Bayesian posterior probabilities are significantly higher than corresponding nonparametric bootstrap frequencies for true clades, but also that erroneous conclusions will be made more often. These errors are strongly accentuated when the models used for analyses are underparameterized. When data are analyzed under the correct model, nonparametric bootstrapping is conservative. Bayesian posterior probabilities are also conservative in this respect, but less so.

This thesis deals with evolutionary relationships within the asterids, a group of plants comprising about one-third of all flowering plants.

Two new families are recognised: Pennantiaceae and Stemonuraceae. The woody Pennantia from New Zealand and Australia is the sole genus of Pennantiaceae. Stemonuraceae consist of a dozen woody genera with a pantropical distribution and a centre of diversity in South East Asia and the Malesian islands. They are characterised by long hairs on their stamens and/or fleshy appendages on their fruits. Both families were formerly included in Icacinaceae. While Pennantiaceae are unrelated to any of the former Icacinaceae and placed in the order Apiales, other former Icacinaceae genera are related to Cardiopteris, a twining herb from South East Asia and Malesia. The monogeneric family Cardiopteridaceae is enlarged as to include also these. Cardiopteridaceae and Stemonuraceae are sister groups and placed in Aquifoliales. The three other families of Aquifoliales are monogeneric and closely related. The Asian Helwingiaceae and the Central/South American Phyllonomaceae are suggested to be merged into Aquifoliaceae (hollies). The genera of Icacinaceae in the traditional sense not placed in any of the above families (all euasterids II) are members of early diverging lineages of the euasterids I and possibly included in the order Garryales.

The three woody Australasian families Alseuosmiaceae, Argophyllaceae, and Phellinaceae are confirmed as members of Asterales, despite traditional placements not close to that order. They are, moreover, supported as each other’s closest relatives.

The results are based mainly on parsimony analysis of DNA sequence data, but morphological studies have revealed characters in support for the molecularly based conclusions. The gene that has provided most new information is the chloroplast ndhF gene. The results are, however, drawn from combined analyses of sequences from one or several additional genes (atpB, matK, rbcL, 18S rDNA). The data have also been explored with Bayesian analysis, a statistical, model-based method that most recently has been developed for phylogeny reconstruction.

The early evolution of the flowering plant order Apiales is discussed based on information from morphology and DNAsequences from four genes (ndhF,rbcL,atpBandmatK). A model-based approach of analysis, Bayesian inference, isused to analyse the data and the results are compared with those from parsimony analysis. In particular, a new familyof the order, the monogeneric Pennantiaceae from New Zealand and Australia, aids in the understanding of howthe order originated. The ancestor of Apiales was probably a shrub or small tree with alternate, simple leaves, paniculateinflorescences, five-merous flowers with free petals, and drupes.

Based on results from cladistic analyses of morphology and DNA sequences (the two chloroplast genes rbcL and ndhF), the three Australasian families Alseuosmiaceae, Argophyllaceae, and Phellinaceae are each monophyletic, belong within Asterales, and together form a monophyletic group. Two new rbcL sequences and thirteen new ndhF sequences were obtained. Congruence tests did not reveal any significant incongruence between the two molecular data sets or between the molecular and morphological data. The character evolution of the Alseuosmiaceae-Argophyllaceae-Phellinaceae group is discussed. The Australasian ancestor of this group was probably a woody plant with simple, alternate, serrate leaves and regular, choripetalous, epigynous flowers borne in panicles. All tree families should be retained in line with the "principle of ease of identification."

The present study is concerned with the evolutionary relationships among the Euasterids II, a group of angiosperms that includes the orders Apiales, Aquifoliales, Asterales, and Dipsacales together with several small, poorly known families yet unplaced as to order.

Parsimony analysis of nucleotide sequence data from the chloroplast genes atpB, ndhF and rbcL together with morphological data are used to construct a phylogeny of the order Asterals, which in the present sense includes 11 families and more than 26 000 species. It is argued that Rousseaceae should be expanded to include also Carpodetaceae (and thus contain four genera), and that Donatia should be re-merged with Stylidiaceae. The present study also strongly supports that the sister taxon to the largest plant family, Asteraceae (Compositae), is the small South American Calyceraceae. A new addition to Asterales is Platyspermation (formerly in Escalloniaceae).

Using the recently developed Bayesian approach to phylogenetic reconstruction, in combination with a dataset consisting of the atpB, ndhF and rbcL nucleotide sequences, a resolved and fairly well supported phylogeny of the Euasterids II could be reconstructed. Based on this analysis, and furthermore supported by morphological characters, the South Hemispheric family Escalloniaceae is recircumscribed to include the monogeneric families Eremosynaceae, Tribelaceae and Polyosmaceae, and in this new circumscription it includes seven genera. The formerly escalloniacean member Quintinia, together with the monogeneric families Paracryphiaceae and Sphenostemonaceae, is argued to consitute a monophyletic family Paracryphiaceae sensu lato, supported by several morphological characters.

Echiochilon, Ogastemma and Sericostoma are revised resulting in the recognition of 15 species of Echiochilon and one Ogastemma species. Several species are placed in synonymy and three new species are described, E. baricum, E. callianthum and E. cyananthum. The single species of Sericostoma is shown to be nested within Echiochilon.

The plastid atpB gene was sequenced for Echiochilon and Ogastemma from the Old World and Antiphytum from the New World, plus for a selection of 33 other Boraginaceae taxa. They were analysed together with selected outgroup taxa to give a framework of the tribes of Boraginoideae. The analysis gave support for establishing the new tribe Echiochileae for Antiphytum, Echiochilon and Ogastemma, and for merging the traditionally accepted tribe Eritrichieae with Cynoglosseae. The ITS region was sequenced for all but one species of Echiochilon and for representatives of Antiphytum and Ogastemma. Phylogenetic analysis of Echiochilon revealed that the strongly zygomorphic-flowered species form a paraphyletic group. The morphological data gave results fairly congruent with the ITS phylogeny.

Biogeographic interpretations of the ITS and atpB phylogenies indicated a trans-Atlantic dispersal of Antiphytum as the most plausible explanation to the Old/New World disjunction. Analyses using DIVA (Dispersal Vicariance Analysis) of the distributions of the Echiochilon species indicated an ancestor to Echiochilon with a wide distribution over northern Africa and Arabia to India.