Northern Prairie Wildlife Research Center
Restricted to the eastern half of North Dakota, slender gerardia also ranges from Quebec to Manitoba south to Florida and Texas at elevations under 5,500 ft.
Slender gerardia is a hairless annual (grow from seed each year) up to 20 inches tall. Leaves are about 3 inches long and very narrow. Flowers, which last a single day, form at the tips of widely spreading pedicels. The 1/2 inch-long flowers are pink to magenta, with 2 yellow lines and purplish spots inside. Fruit is a round capsule about 3/16 inch long filled with dark, triangular seeds. Plants resemble flax in general shape and height.
Look for slender gerardia during August in low areas in native tallgrass prairie that has been mowed, burned, or grazed earlier in the season. This reduces competition for sunlight and allows shorter plants to flower. The plant is never of importance as livestock forage. Gerardias turn black when dry and so are a disappointment to those who collect and press plants for a hobby. I found no references to any economic uses for the plant.
Slender gerardia belongs to the figwort family (Scrophulariaceae), so called because the early herbalist-physicians believed the plants cured scrophula and removed figwarts. The family contains about 4,000 species and includes foxglove (source of the drug digitalis) and the snapdragons. Gerardias were named in honor of John Gerard (1545-1612), author of the Great Herbal (1597), a famous early book on plants. There are about 60 species in the genus Agalinis (formerly Gerardia); all are found in temperate areas of the Western Hemisphere. In botanical Latin, the generic name means "remarkable flax" and the specific epithet tenuifolia means "slender-leaved."
Slender gerardia was first described for science in 1794 by the early Danish botanist Martin Hendriksen Vahl (1749-1804). Vahl was a student of the famous Swedish father of modern plant taxonomy, Carl von Linne (Linnaeus).