The genome assembly of Carex breviculmis provides evidence for its phylogenetic localization and environmental adaptation.

Carex breviculmis is a perennial herb with good resistance and is widely used for forage production and turf management. We assembled the genome of 469.01 Mb, revealing 37,372 genes with a BUSCO completeness score of 99.0%. The genome comprises 52.03% repetitive sequences, primarily influenced by recent LTR insertions that have contributed to its expansion. Phylogenetic analysis suggested that C. breviculmis diverged from C. littledalei approximately 6.61 Mya. Investigation into repetitive sequences and expanded gene families (EGFs) highlighted a rapid expansion of tandem duplicate (TD) genes, particularly in areas related to sugar metabolism, various amino acid synthesis, and phenylpropanoid biosynthesis. Additionally, our analysis identified crucial genes involved in secondary metabolic pathways such as glycolysis, phenylpropanoid biosynthesis, and amino acid metabolism, which have undergone positive selection. We reconstructed the sucrose metabolic pathway and identified significant gene expansions, included 16 INV, 9 SPS, and 12 SuSy genes associated with sucrose metabolism, showed varying levels of expansion. In summary, the expansion of these genes, coupled with subsequent positive selection, contributed to C. breviculmis' ability to adapt to environmental stressors. This study lays the foundation for future research on the evolution of Carex plants, their environmental adaptations, and potential genetic breeding.