Genome Assembly of <i>Spinifex sericeus</i> Provides Insights into Repetitive Content and Haplotype Variation in a Dioecious Coastal Grass

Spinifex sericeus (beach spinifex) is a perennial, dioecious grass native to the coastal ecosystem of Oceania that has an important role in dune stability. We present a near telomere-to-telomere, haplotype-resolved nuclear genome and complete organelle genomes of S. sericeus. The nuclear genome is highly repeat-rich, dominated by long terminal repeat (LTR) retrotransposons. Comparative analysis of the two haplotypes reveals extensive structural variation and high levels of duplication that are suggestive of active and expanding LTRs that may drive genome evolution and expansion in this species. The chloroplast genome exhibits heteroplasmy, having two distinct circular configurations spanning 138 kbp each. The complex mitochondrial genome consists of a large linear component spanning 1.85 Mbp and a small circular 134 kbp component. These genomic resources provide a foundation for advancing research on sex determination and stress adaptation in grasses, as well as practical applications in crop improvement and genetically informed coastal dune restoration.