Background. Caryophyllaceae is a large and cosmopolitic flowering plant family, however the systematics of many of its basal groups has been unclear, due to a lack of unambiguous morphology. Some members of Caryophyllaceae are used medicinally, e.g. Corrigiola roots in Morocco. Monitoring the trade in medicinal plants is complicated due to the absence of useful identification characters in plant products such as roots, bark, and powders. This thesis aims at elucidating the systematics and the ethnobotany of some of the basal clades in Caryophyllaceae. Methods. A comprehensive sampling from herbarium as well as market and field collected material was used in systematic studies combining morphological investigation, molecular phylogenetic and molecular dating analyses. Results. The data show that Polycarpon is polyphyletic, that Sphaerocoma is sister to Pollichia and shows some intraspecific variation, that Sanctambrosia falls within the genus Spergularia, and that both Spergula and Spergularia are monophyletic. Preliminary data suggest that Polycarpaea is polyphyletic and should be split into three larger and several smaller genera, that the members of Paronychia subgen. Anaplonychia will need to be transferred to Herniaria to maintain monophyly, and that Caryophyllaceae emerged during the Paleocene. All the major extant lineages originated in the Oligocene and diversified later. Using molecular identification it was possible to identify around 50% of the Moroccan medicinal roots to species level and an additional 30% to genus level. Discussion and conclusions. The polyphyletic Polycarpon needs to be split into at least three separate genera, but no name changes were made pending further research. The two species of Sphaerocoma were merged into one species with two subspecies. The San Ambrosio Island endemic Sanctambrosia, the only tree-like plant in Caryophyllaceae, is probably the result of a long distance dispersal event and its woody habit and gynodioecy are probably caused by inbreeding depression. Sanctambrosia manicata is transferred to Spergularia. Molecular identification put into practice on traded medicinal roots has a somewhat lower success rate than most theoretical studies, indicating that a global barcoding database would need to include reference sequences from a broad range of populations for each species.

Isopods in the genus Tylos are distributed in tropical and subtropical sandy intertidal beaches throughout the world. These isopods have biological characteristics that are expected to severely restrict their long-distance dispersal potential: (1) they are direct developers (i.e., as all peracarids, they lack a planktonic stage); (2) they cannot survive in the sea for long periods of immersion (i.e., only a few hours); (3) they actively avoid entering the water; and (4) they are restricted to the sandy intertidal portion that is wet, but not covered by water. Because of these traits, high levels of genetic differentiation are anticipated among allopatric populations of Tylos. We studied the phylogeographic patterns of Tylos in the northern East Pacific region between southern California and central Mexico, including the Gulf of California. We discovered high levels of cryptic biodiversity for this isopod, consistent with expectations from its biology. We interpreted the phylogeographic patterns of Tylos in relation to past geological events in the region, and compared them with those of Ligia, a co-distributed non-vagile coastal isopod. Furthermore, we assessed the usefulness of the shape of the ventral plates of the fifth pleonite for distinguishing genetically divergent lineages of Tylos in the study area. Finally, mitochondrial phylogenenetic analyses to identify the most appropriate outgroup taxa for Tylos in the study area, which included 17 of the 21 currently recognized species, provided important insights on the evolutionary history of this genus.