Linaria is a genus of flowering plants found distributed in many regions of Africa, Asia, and Europe, in a wide variety of climates and environments from alpine meadows to woodlands. Most species prefer temperate regions and several are grown as ornamentals in temperate gardens all over the world. Known commonly as toadflax, this genus contains more than 100 species and is placed in the plantain family.
These plants have an herbaceous growth habit, producing tall stalks with large arrays of yellow, purple, or orange flowers, depending on the species. Some are annuals and will reseed themselves each year, while others are perennial and will continue growing year after year. Species adapted to warmer climates can sometimes behave like annuals in cooler regions, dying off in the fall and winter after leaving seeds behind for spring.
Some species of Linaria are known to be toxic and can be a concern for farmers when they appear in fields and meadows with livestock. Others attract butterflies, bees, and other beneficial insects and may be encouraged to grow in regions where insect populations are low. This genus also includes several invasive species, including one known by the colorful sobriquet of “butter and eggs,” a reference to its cheery yellow flowers. Invasive species are a concern in areas where native plants cannot compete with fast-growing Linaria.
This genus also has a history of use in traditional herbal medicine. Preparations of toadflax can be used as diuretics and laxatives, although dosages must be measured with care, as the plant can be dangerous when taken in large amounts. It is not recommended at all for use in pregnant women. It can also be used in topical herbal preparations for skin irritation and growths like hemorrhoids. Herbalists and stores that stock herbal medicines sometimes carry Linaria, along with directions for usage.
At least one species, L. purpurea or purple toadflax, is grown as an ornamental plant. This species, with tall spikes of colorful purple flowers, can be grown in clumped or massed plantings. Gardners in United States Department of Agriculture (USDA) zones three through eight should be able to grow it successfully, using seeds or seedlings from a garden supply store, nursery, or gardening exchange. People may want to be careful about where they plant it, to avoid threatening native plants with a potentially invasive species. Cutting down Linaria flower stalks before they go to seed can help prevent the plant from spreading uncontrollably.