The phylogeny of Gnetales has been debated during recent years. Traditionally, they have often been regarded as the sister group of angiosperms, but alternative opinions, mainly based on wood and stem characters, have also been put forward. Recently, several molecular studies have indicated that Gnetales might be nested within conifers. In this study more than a hundred new sequences of rbcL, atpB, 26S and 18S rDNA have been analyzed together with available GenBank sequences. Seed plant phylogeny and the systematic position of Gnetales have been investigated using parsimony methods. The four datasets were analyzed separately and combined, with different weighting schemes, and with variously sized subsets including between 20 to 750 land plant species. The aim was to thoroughly evaluate the phylogenetic information of each gene, and to study if results were influenced by taxon sampling. Our combined tree is well resolved recognizing major land plant clades, including conifers, with high support. Relationships within angiosperms, cycads, conifers and ferns are well supported, but relationships between major groups might be interpreted in several ways. The ‘gne-pine’ theory is clearly refuted by our data, but before making any further conclusions on the evolution of seed plants, additional types of data need to be considered. Molecules alone might not be able to solve seed plant phylogeny.

Key words: Conifers, DNA, Gnetales, phylogeny, seed plants