Genetic Diversity Analysis of American Ginseng (Panax quinquefolius L.) Accessions Based on Phenotypic Traits and SSR Markers

American ginseng (Panax quinquefolius L.) is an important medicinal crop, but its improvement in China is limited by variety degeneration and a shortage of elite cultivars. In this study, phenotypic traits and simple sequence repeat (SSR) markers were integrated to evaluate the genetic diversity of 51 selected accessions from major Chinese production regions. Phenotypic analysis showed that five of the 18 quantitative traits had phenotypic coefficients of variation exceeding 40%, mainly involving root traits such as fresh root weight and lateral root number. Broad-sense heritability for these root traits ranged from 61.70% to 74.80%, indicating substantial genetic contribution under standardized conditions. Principal component analysis identified five candidate elite accessions: CY3 and KD1 for tall stature and high yield, DH1 and LH2 for high ginsenoside content, and AT1 for well-developed lateral roots. A 12-accession representative subset was further proposed for conservation and pre-breeding. SSR-based clustering showed weak geographic differentiation, and Mantel analysis revealed no significant correlation between phenotypic and SSR-based genetic distances. These materials, together with the proposed accession-level conservation strategy, provide useful resources for germplasm preservation, parental selection, QTL mapping, and marker-assisted breeding.