Figure 1

Phylogenetic distribution of the standard and non-canonical genetic codes in green algae. The occurrence of a non-canonical genetic code (TAR→Gln) is indicated with gray squares. The taxa with the non-canonical code do not form a monophyletic group Three alternative scenarios can explain this phylogenetic distribution: (1) A single origin of the non-canonical code along the branch leading to the orders Trentepohliales, Dasycladales, Bryopsidales, Cladophorales and the genus Blastophysa and a subsequent reversal to the universal code in the Bryopsidales (indicated with black arrow and cross). (2) Three independent gains of the non-canonical code in the Trentepohliales, the Dasycladales and the Cladophorales + Blastophysa (indicated with gray arrows). (3) A stepwise process of evolution of the non-canonical code with a single initiation of the process along the branch leading to the orders Trentepohliales, Dasycladales, Bryopsidales, Cladophorales and the genus Blastophysa, followed by a completion of the process in all lineages except the Bryopsidales (black arrow combined with gray arrows). The reference phylogeny of the green plant lineage was obtained by maximum likelihood inference of a 25% site stripped dataset containing 7 nuclear genes, SSU nrDNA and plastid genes rbcL and atpB [22]. Numbers at nodes indicate ML bootstrap values (top) and posterior probabilities (bottom); values below respectively 50 and 0.9 are not shown.