James B. Holland

Maize ( Zea mays L. subsp. mays ) is the most important crop in the United States, but maize food and distillation products often rely on varieties that are not bred explicitly for these purposes. Farmers targeting niche food grain markets have expressed interest in historical open‐pollinated varieties of maize, but few such populations are widely available, and even fewer are well‐characterized. We planted field trials of 76 open‐pollinated heirloom varieties available from seed catalogs and the United States Department of Agriculture germplasm collection along with four F1 hybrid cultivars. We measured 24 traits across 3 years and three locations to characterize the selected varieties and measure their phenotypic relationships. We identified a subset of 19 traits with heritability >0.5 and pairwise correlation coefficients not exceeding 0.9 for phenotypic analysis. Our results demonstrate that many historical accessions contain substantial genetic variation that should permit improvement from within‐population selection. Variety name and origin are often not useful indicators of phenotypic relationships or potential crop value, although Hickory King varieties have maintained their identity even following global dispersion. Cluster analysis identifies nine morphologically distinct groups within the varieties tested, which are largely in agreement with previously proposed landrace groupings. Our results suggest a complex intermixing of Southern Dents with other maize types, rather than a clear distinction between Southern Dents and Derived Southern Dents, however. Genetic analysis of larger samples of US open‐pollinated populations will help better define the natural classification of maize indigenous to the United States.