The genus Linaria had been split in 1988 by David A. Sutton, with the native Western Hemisphere species (three in North America and one in South America) placed in the genus Nuttallanthus.
For a discussion on the change of the American toadflax species from the genus Linaria to Nuttallanthus see Nuttallanthus canadensis at Wildflowers of the United States
A study by Mario Fernadez-Mazuecos, Jose ́ Luis Blanco-Pastor and Pablo Vargas published in 2013 titled A Phylogeny of Toadflaxes ( Linaria Mill.) Based on Nuclear Internal Transcribed Spacer Sequences: Systematic and Evolutionary Consequences placed the American toadflaxes back in Linaria.