Chromosome-level Genome Assembly and Annotation of the Arctic Moss <i>Ptychostomum knowltonii</i>

The polar regions host a diverse array of moss species that have evolved to thrive in extreme environments. These mosses exhibit remarkable adaptations, including tolerance to freezing temperatures, desiccation, and ultraviolet radiation. Despite their ecological significance, genomic data on these organisms are still limited, impeding our understanding of their evolutionary history and adaptive mechanisms in the context of climate change. In this study, we present the first chromosome-scale genome assembly and annotation of the Arctic moss Ptychostomum knowltonii. The assembled genome is 408.8 Mb in size, anchored to 12 pseudochromosomes, with a scaffold N50 of 32.61 Mb. Repetitive elements account for 56.24% of the genome. The genome contains 28,014 protein-coding genes, with a BUSCO completeness of 96.20%. This genomic resource will enable future comparative genomic studies, enhancing our understanding of how polar mosses may respond to a warming climate and shedding light on their evolutionary trajectories in persistently extreme environments.