Evolution of inverted repeat borders in selected land plants. Species names are abbreviated in circles. Vertical lines depict the borders of the IR relative to the detailed gene map from E. arvense shown at bottom. Thick, solid vertical lines in dark blue mark the putative ancestral IR borders. Thin, dashed vertical lines and circles indicate the IR borders in species that deviate from the ancestral position. Horizontal arrows indicate the extent and direction of IR expansion. Numbers at the arrow tails define the order of successive expansions. All non-seed plant cpDNAs were included, except for Isoetes, Selaginella, and Polypodiopsida because their genomes have gene order rearrangements that make an alignment impossible. Included species: Cycas taitungensis (Cta), Angiopteris evecta (Aev), Psilotum nudum (Pnu), Equisetum arvense (Ear), Equisetum hyemale (Ehy), Ophioglossum californicum (Oca), Huperzia lucidula (Hlu), Anthoceros formosae (Afo), Physcomitrella patens (Ppa), Syntrichia ruralis (Sru), Aneura mirabilis (Ami), Marchantia polymorpha (Mpo), Ptilidium pulcherrimum (Ppu). Higher group names: seed plants (SP), monilophytes (MP), lycophytes (LP), hornworts (HW), mosses (MS), liverworts (LW).