Chloroplast genome rearrangements and the evolution of giant lobelias from herbaceous ancestors

Phylogenetic relationships among 16 species of Lobelia and single representatives of Monopsis and Sclerotheca (Lobeliaceae) were assessed by mapping restriction sites and major structural rearrangements (deletions and inversions) in the large single-copy region of the chloroplast genome. Eleven inversions and five different gene arrangements were found. A deletion involving ORF512 is associated with many of the inversions, and all inversion endpoints are located in intergenic spacer regions. Analysis of 132 phylogenetically informative restriction sites produced three equally parsimonious trees of 219 steps, with a consistency index of 0.60. The restriction-site and inversion data yield congruent trees, indicating that the giant lobelias from around the world are derived from diploid herbaceous ancestors. The giant lobelias consist of a Chilean hexaploid group and a pantropical tetraploid group. The woody genus Sclerotheca is clearly derived from a giant Lobelia ancestor, while the herbaceous Monopsis is probably derived from herbaceous lobelias. The giant lobelias from eastern Africa are weakly supported as monophyletic with the inclusion of the Brazilian L. organensis. Relationships among the Pacific and Asian giant lobelias are not fully resolved and await more detailed study.