The first aim of the Diploma-thesis was to evaluate, wether a recent systematical concept based on a cladistic analysis of morphological characters, can be used to include fossil taxa. In a second step the combination of fossil and recent morphological data is compared to an independent molecular data set (here: partial sequences from the 25 S rDNA) to re-investigate phylogentic hypothesis assembled by the morphological data.

A morphological matrix including all recent genera of the Cycadales (Stevenson, 1990) was extented for several fossil taxa and taxonomic associations. Only characters were used, for which a detailed description of the fossil material was available. As "molecular reference" a partial sequence of the 25S ribosomal DNA was used. The leaf material used for the molecular analysis was obtained from plants cultivated either in the Botanical Garden of the University of Tübingen or the "Palmengarten" in Frankfurt (Main). PCR products were not directly sequenced, but cloned using a E. coli strain DH5α PUC18 vector system for better handling. Both data sets, the morphological matrix and the molecular sequence data, were analysed with PAUP^® Version 4.0 beta2 (Swoffort, 1991).

The cladistic analysis of the morphological matrix resulted in a most parsimonious tree, coherent with the main features of the recent systematics. However, the individual placement of certain extant and extinct taxa revealed new insights on phylogenetic concepts applied to the order Cycadales. Furthermore, the reliability of several morphological characters could be tested. Finally a phylogenetic theory is presented, which combines recent and fossil relationships, not only based on morphological data but supported by other data sources, mainly the molecular evidence.