The Pleurocarpous Moss Tree of Life project aims to understand a major radiation event responsible for about half of all living moss species. We used transcriptome sequences from many species of pleurocarpous and acrocarpous mosses to generate a species tree of the mosses using hundreds of genes. We then used this tree to investigate changes in the genomes of pleurocarpous mosses associated with the radiation: whole genome duplication, gene family expansion, horizontal gene transfer, and changes in selection on genes. These genomic clues give us insight into the rapid radiation of pleurocarpous mosses.