This study investigates the evolution of subgenome dominance in 11 bamboo species, ranging from diploid to tetraploid and hexaploid, using chromosome-level de novo genome assemblies and transcriptome samples. The results highlight the remarkable karyotype stability of woody bamboo subgenomes, with parallel subgenome dominance in tetraploid clades and a gradual shift in hexaploid clades. Allopolyploidization and subgenome dominance have shaped the evolution of tree-like lignified culms, rapid growth, and synchronous flowering in woody bamboos. The study provides insights into the dynamics of subgenome dominance in ancient polyploid systems, including its dependence on genomic context and the ability to switch dominant subgenomes over evolutionary time. The findings also reveal the genomic basis of unique traits in woody bamboos, such as lignin biosynthesis and shoot growth, and the role of subgenome dominance in their adaptation and radiation into forest habitats.This study investigates the evolution of subgenome dominance in 11 bamboo species, ranging from diploid to tetraploid and hexaploid, using chromosome-level de novo genome assemblies and transcriptome samples. The results highlight the remarkable karyotype stability of woody bamboo subgenomes, with parallel subgenome dominance in tetraploid clades and a gradual shift in hexaploid clades. Allopolyploidization and subgenome dominance have shaped the evolution of tree-like lignified culms, rapid growth, and synchronous flowering in woody bamboos. The study provides insights into the dynamics of subgenome dominance in ancient polyploid systems, including its dependence on genomic context and the ability to switch dominant subgenomes over evolutionary time. The findings also reveal the genomic basis of unique traits in woody bamboos, such as lignin biosynthesis and shoot growth, and the role of subgenome dominance in their adaptation and radiation into forest habitats.