A genome assembly of Greene's tuctoria, Tuctoria greenei, an amphibious endemic and endangered California vernal pool grass

The Orcuttiinae subtribe of the grass tribe Cynodonteae (Poaceae) represents an ancient and unique group of amphibious grasses adapted to the winter-wet, summer-dry conditions of seasonally flooded vernal pools. The subtribe consists of nine species represented across three genera (Neostapfia, Tuctoria, Orcuttia), most of which are endemic to, and found exclusively in, vernal pools throughout the California Floristic Province (from the Modoc Plateau to Baja California, Mexico) and in the Magdalena Plain in the southern Baja California peninsula. All species are rare and most have state and federal Threatened and/or Endangered protected status in the U.S.-except Tuctoria fragilis, which inhabits Baja California Sur, Mexico, and does not have official protected status in Mexico. Here, we report a new chromosome-level reference genome assembly and annotation for Greene's tuctoria (Tuctoria greenei) developed in collaboration with the California Conservation Genomics Project. The assembly includes two haplotypes: haplotype one spans 2.59 Gb with contig N50 of 3.22 Mb, scaffold N50 of 216.09 Mb, largest contig N50 of 19.5 Mb, and BUSCO completeness of 96.8%. Haplotype two spans 258.89 Gb with contig N50 of 3.27 Mb and scaffold N50 of 213.15 Mb, with a BUSCO completeness of 97.4%. This genome assembly confirms earlier chromosome counts of n = 24 for T. greenei and represents a powerful new tool that can be used to test hypotheses of gene flow, adaptation and comparative genomics between recently diverged species, and to assist in regional conservation priorities and restoration efforts.