We propose an infrageneric classification that recognizes two sections in New World Amerallium. Because there is substantial incongruence between morphological and molecular groups, we advocate retaining informal alliances rather than adopting formal subsections until further morphological and molecular analyses can be carried out.

In the originally published article, the author contributions were listed incorrectly. The corrected statement is below, and the original article is corrected.EJW and BC conceived of and designed the study with contributions from CR and AEM. EJW and BC coordinated herbarium and field sampling and AEM conducted the DNA sequencing laboratory work. AEM and APR conducted preliminary data analysis and EWH, JW, JCG, and WH refined the dataset and expanded the analyses in the final version. EWH, EJW, BC, and AEM drafted sections of the manuscript text and tables; EWH and WH made all figures; and EWH, JW, JCG, and WH crafted the final narrative. All authors provided critical review and revision of the draft manuscript.

Lupinus polyphylhis and L. wyethii are closely related members of a species complex widely distributed in western North America. Principal components analysis of morphological characters showed that these two taxa intergrade extensively, with many intermediate forms occurring. DNA sequences of the internal transcribed spacer (ITS) region in 28 individuals were variable at five base positions, both within and between taxa; some of these sequences have also been reported from related species. Molecular variation showed a geographic pattern but did not strongly reflect morphological differences. Morphological features that have been used to separate species in this group may primarily reflect local adaptation rather than underlying phylogenetic divergence. The lack of clear differentiation between these two lupines suggests that they are best treated as varieties of a single species, L. polyphyllus.