Phylogenetic implications of the multiple losses of the mitochondrial coxII.i3 intron in the angiosperms

Previous studies have shown that the mitochondrial coxII.i3 intron is absen t in all rosids examined, in Philadelphus (Hydrangeaceae, Cornales), and in Catharanthus and Vinca (Apocynaceae, Gentianales). We surveyed for the pre sence or absence of this intron in 177 species representing all orders of a ngiosperms, where it is primitively present. The intron appears to have bee n lost independently in Gnetales, Laurales, Zingiberales, Ranunculales, Sax ifragales, rosids, Santalales, Caryophyllales, Ericales, Cornales, Gentiana les, Lamiales, Boraginales, Aquifoliales, Asterales, Dipsacales, as well as in the genus Escallonia. Depending upon the phylogenies used to interpret the losses, and due to lack of resolution in some groups, the intron could have been lost up to 27 times in the angiosperms (excluding the loss in Gne tales). The losses sometimes corroborate the monophyly of groups (rosids an d Lamiales) or of subgroups within orders (in the Ranunculales, Caryophylla les, Cornales, Gentianales, and Asterales). In other groups, such as the Sa xifragales, Ericales, and Dipsacales, the patterns of losses are more compl ex and would require further study. The presence or absence of the coxII.i3 mitochondrial intron seems a useful phylogenetic marker in some groups, bu t caution in interpretation is needed as multiple parallel losses have occu rred throughout the angiosperms.