toadflax, (genus Linaria), genus of nearly 200 herbaceous flowering plants in the family Plantaginaceae native to the north temperate zone, particularly the Mediterranean region. The common name toadflax refers to their flax-like leaves, and the flowers are two-lipped and spurred like snapdragons. Several species are considered invasive in areas outside their native ranges.
Among the prominent members are common toadflax, or butter-and-eggs (Linaria vulgaris), with yellow and orange flower parts, which is native to Eurasia and is now widely naturalized in North America. From North Africa come the cloven-lip toadflax (L. bipartita) and purple-net toadflax (L. reticulata), both of which have purple and orange bicoloured flowers.
A number of species formerly of the genus Linaria are now placed in the genus Nuttallanthus, including blue, or old-field, toadflax (N. canadensis, formerly L. canadensis), a delicate light blue flowering plant found throughout North America.