The origin of land plants: phylogenetic relationships among charophytes, bryophytes, and vascular plants inferred from complete small-subunit ribosomal RNA gene sequences.

Complete nuclear-encoded small-subunit 18S rRNA (= SSU rRNA) gene sequences were determined for the prasinophyte green alga Mantoniella squamata; the charophycean green algae Chara foetida, Coleochaete scutata, Klebsormidium flaccidum, and Mougeotia scalaris; the bryophytes Marchantia polymorpha, Fossombronia pusilla, and Funaria hygrometrica; and the lycopod Selaginella galleottii to get a better insight into the sequential evolution from green algae to land plants. The sequences were aligned with several previously published SSU rRNA sequences from chlorophytic and charophytic algae as well as from land plants to infer the evolutionary relationships for major evolutionary lineages within the Chlorobionta by distance matrix, maximum parsimony, and maximum likelihood analyses. Phylogenetic trees created by the different methods consistently placed the Charophyceae on the branch leading to the land plants. The Charophyceae were shown to be polyphyletic with the Charales ("charalean" algae) diverging earlier than the Coleochaetales, Klebsormidiales, Chlorokybales, and Zygnematales ("charophycean" algae) which branch from a point closer to the land plants in most analyses. Maximum parsimony and maximum likelihood analyses imply a successive evolution from "charophycean" algae, particularly Coleochaetales, to bryophytes, lycopods, and seed plants. In contrast, distance matrix methods group the bryophytes together with the "charophycean" algae, suggesting a separate evolution of these organisms compared with the club moss and the seed plants.