A New Hexaploid Species of <i>Isoetes</i> (Isoetaceae) From Fujian, China, Based on Morphological and Molecular Evidence

A new endemic species of <i>Isoetes</i> from Fujian, China, which was previously identified as <i>I. orientalis</i>, is described and illustrated. In this study, we observed its leaf cross-cut characteristics under a microscope and spore morphology characteristics under a scanning electron microscope, counted its chromosome number, and compared population genetic differences between this hexaploid and <i>I. orientalis</i> based on single nucleotide polymorphisms (SNPs) extracted from whole-genome resequencing data. We found that this hexaploid differs from <i>I. orientalis</i> in both leaf morphology and spore ornamentation, and that the two also exhibit significant differences in population genetics. Based on this comprehensive evidence, we identified the hexaploid as a new species and named it <i>I. fokiensis</i>. Here, we formally describe this hexaploid species and provide an identification key to the <i>Isoetes</i> species reported from China.