Molecular Phylogenetics and Historical Biogeography of Basal Angiosperms

Abstract

Scientific progress during the last two decades has greatly improved our knowledge on phylogenetic relationships among major lineages of flowering plants. Besides the two major groups of angiosperms, the eudicots and the monocots, there are several not closely related lineages that are generally referred to as the "basal angiosperms". Among those lineages, <i>Amborella</i>, Nymphaeales and Austrobaileyales are currently assumed to be successive sisters to the rest of angiosperms, thus forming a "basal grade". However, the phylogenetic relationships among and within the basal angiosperm lineages are still not convincingly resolved, which is to a large extent due to the persisting need for efficient molecular markers at this taxonomic level.<br /> The focus of the present thesis is on the phylogenetic and biogeographic history of the order Nymphaeales, a relatively small order comprising water lilies and other water plants. To clarify the phylogeny of Nymphaeales a new molecular marker, the <i>petD</i> intron, was developed. The molecular evolution of this non-coding region of the chloroplast genome was examined and its suitability as a new marker for resolving basal angiosperm relationships was proved. This study also revealed a great potential of microstructural changes as phylogenetic markers. In a second step the <i>petD</i> intron was chosen as a marker - together with other fast evolving chloroplast regions (<i>rpl16</i> intron, <i>trnK</i> intron, <i>matK</i> gene, and the <i>trnT-trnF</i> region) to elucidate details of phylogenetic relationships in Nymphaeales. With this comprehensive analysis of Nymphaeales the monophyly of the Cabombaceae could be confirmed, but there is no convincing support for the monophyly of Nymphaeaceae with respect to <i>Nuphar</i>. Furthermore, the genus <i>Nymphaea</i> is inferred to be polyphyletic with respect to the genera <i>Ondinea</i>, <i>Victoria</i> and <i>Euryale</i>. In fact, <i>Victoria</i> and <i>Euryale</i> are inferred to be closely related to a clade comprising all night blooming water lilies (<i>Nymphaea</i> subgenera <i>Hydrocallis</i> and <i>Lotos</i>). The Australian endemic <i>Ondinea</i> forms a highly supported clade with the Australian water lilies <i>Nymphaea</i> subg. <i>Anecphya</i>. <br /> A detailed examination of relationships among Australian water lilies using chloroplast and nuclear markers (ITS, <i>trnT-trnF</i>) confirmed the close affinity of <i>Ondinea</i> to <i>N.</i> subg. <i>Anecphya</i>, and within this subgenus especially to <i>Nymphaea hastifolia</i>. The ITS data set resolved two well supported clades in <i>Anecphya</i>, the small-seeded and large-seeded group, with <i>Ondinea</i> and <i>N. hastifolia</i> being part of the small-seeded group. Observed polymorphisms among ITS paralogues points to recent hybridisation or introgression in this group. The rather young radiation of water lilies in Australia gave rise to one of the centres of diversity in Nymphaeales. Other centres of diversity are northern South America and South-Central Africa, which correspond to likewise recent radiations in the water lily subgenera <i>Hydrocallis</i> and <i>Brachyceras</i>. The radiation of core Nymphaeaceae, i.e. <i>Nymphaea</i>, <i>Victoria</i>, <i>Euryale</i> and <i>Ondinea</i>, occurred in the Tertiary around the Eocene-Oligocene boundary and is correlated with strong global cooling, the demise of the boreotropical flora and the segregation of northern hemispheric continents. The northern hemisphere, and possibly also South America, is inferred to be the ancestral range of Nymphaeales. Other Gondwanan continents such as Africa or Australia have been invaded by water lilies rather recently. <br /> Some findings of this thesis are of more general significance - beyond Nymphaeales or basal angiosperms: The present study provides another peace of evidence for the general utility of non-coding, fast-evolving chloroplast genomic regions and of microstructural changes as phylogenetic markers. Furthermore, the Nymphaeales study exemplifies the importance of judicious taxon sampling for correct phylogenetic inference. Only the combination of well-supported evidence from molecular phylogenetics, earth history and the fossil record with a thorough consideration of biological and ecological factors allows reasonable conclusions on the evolution of a lineage in space and time.