Blue Toadflax has reasonably attractive foliage and flowers. Its appearance is very similar to Nuttallanthus texensis (Southern Blue Toadflax), but the latter has larger flowers (up to 1" long) and bumpy seeds. Blue Toadflax is also related to the introduced Linaria vulgaris (Yellow Toadflax), but the latter has larger yellow flowers (up to 1" long or more). There are other Toadflaxes from Eurasia that occur primarily in sterile waste areas, but they usually have smaller flowers (¼" or less). Blue Toadflax superficially resembles Lobelia kalmii (Kalm's Lobelia), but the flowers of the latter lack nectar spurs and it usually blooms later in the year. Another scientific name for Blue Toadflax is Linaria canadensis.