RYDIN, CATARINA1,2*, MARI KALLERSJO2, and ELSE MARIE FRIIS2. 1Stockholm University, Dep of Botany, SE-106 91 Stockholm, Sweden; 2Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden. - Seed plant relationships and the systematic position of Gnetales; evidence from nuclear and chloroplast DNA demonstrates the monophyly of Conifers.
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
Key words: Conifers, DNA, Gnetales, phylogeny, seed plants