This thesis investigates the phylogenetic systematics at the ordinal level (Poales), clade level (restiids), familial level (Bromeliaceae and Poaceae), and subfamilial level Pooideae with the aim to answer questions that have as of yet been unresolved. A plastid reference tree (matkpsbA) was compared with nuclear single-copy gene trees (Topo6, PhyB, Acc1). Within the Poales, the nuclear data could not bring any new insights. The data support two families within the restiid clade (Anarthriaceae, Restionaceae) and the centrolepids as subfamily Centrolepidoideae. Topo6 show the monophyly of all major groups of grasses. All established tribes and subtribes of the Pooideae are supported by the combined nuclear dataset. Different clone types of Ampelodesmos (Acc1, Topo6) suggests a hybrid origin of this monotypic genus, with a potential ancestor within the Stipeae and the Duthieeae. The used Marker regions of the nuclear sinlge-copy genes were altogether suitable for the phylogenetic investigations.