Seventy HAG effector family members from Pyricularia species are found in P. oryzae and three closely related species (P. sp. LS/P. sp. Jiangsuensis, P. grisea, and P. pennisetigena) that share at least eight orthologous HAG family members with P. oryzae. The genome sequence of a more distantly related species, P. penniseti, lacks HAGs, suggesting a time frame for the origin of the gene family in the genus. In P. oryzae, HAG4 is uniquely found in the genetic lineage that contains populations adapted to Setaria and Oryza hosts. We find a nearly identical HAG4 allele in a P. grisea isolate suggesting transfer of HAG4 from P. grisea to P. oryzae. HAG4 encodes a suppressor of plant cell death. Yeast two-hybrid screens with several HAGs independently identify common interacting clones from a rice cDNA library suggesting conservation of protein surface motifs between HAG homologs with as little as 40% protein sequence identity. HAG family orthologs have diverged rapidly and HAG15 orthologs display unusually high rates of sequence divergence compared with adjacent genes suggesting gene-specific accelerated divergence. The sequence diversity of the HAG homologs in Pyricularia species provides a resource for examining mechanisms of gene family evolution and the relationship to structural and functional evolution of HAG effector family activity.