Nuclear and chloroplast phylogeny of P. australislineages
Given that the native North American population diverged early from
other populations (C. Wang, Liu, Yin, Eller, Brix, Wang, Salojärvi, et
al., 2021), we rooted the nuclear phylogeny on the USnat lineage. The
lineages then diverged in the following order: Med, EU, AU and CN, with
AU clustering closely with CN (Fig. 1a ). In contrast, the
unrooted chloroplast phylogenetic tree grouped the CN lineage with other
lineages (Fig. 1b ), while the AU lineage formed its own
distinct clade. Discrepancies between the nuclear and chloroplast
phylogenies were observed for some individuals, where they clustered
with the CN lineage in the nuclear phylogenetic tree but grouped with
the AU lineage in the chloroplast phylogenetic tree. These include the
populations labeled as CN_brackish, Heze, and Panjin. These mismatches
suggest substantial gene flow between the two lineages, indicating
ancient hybridization events. In contrast, the Australian populations,
including both brackish water and freshwater ecotypes, all clustered
within the same genetic group, suggesting that the octoploid AU lineage
possesses genes conferring salinity tolerance (Fig. 1a,b ).