The One Thousand Plant Transcriptomes Initiative sequenced the vegetative transcriptomes of 1,124 plant species, spanning a broad taxonomic range, to provide a robust phylogenomic framework for studying the evolution of green plants. The analysis reveals well-supported species relationships but highlights discordance among plastid and nuclear gene trees at some nodes, indicating the complexity of plant genome evolution. The study identifies numerous gene-family expansions and contractions, with significant expansions occurring before the origins of green plants, land plants, and vascular plants. Whole-genome duplications (WGDs) are inferred to have occurred repeatedly throughout the evolution of flowering plants and ferns. The findings underscore the importance of gene and genome duplications in driving evolutionary innovations, such as the development of multicellularity, reproductive organs, and specialized tissues. The initiative's comprehensive approach advances our understanding of the phylogenetic framework of green plants and the genetic changes underlying major evolutionary transitions.The One Thousand Plant Transcriptomes Initiative sequenced the vegetative transcriptomes of 1,124 plant species, spanning a broad taxonomic range, to provide a robust phylogenomic framework for studying the evolution of green plants. The analysis reveals well-supported species relationships but highlights discordance among plastid and nuclear gene trees at some nodes, indicating the complexity of plant genome evolution. The study identifies numerous gene-family expansions and contractions, with significant expansions occurring before the origins of green plants, land plants, and vascular plants. Whole-genome duplications (WGDs) are inferred to have occurred repeatedly throughout the evolution of flowering plants and ferns. The findings underscore the importance of gene and genome duplications in driving evolutionary innovations, such as the development of multicellularity, reproductive organs, and specialized tissues. The initiative's comprehensive approach advances our understanding of the phylogenetic framework of green plants and the genetic changes underlying major evolutionary transitions.