Smooth Beard-Tongue (Tall White Beard-Tongue; Foxglove Beardtongue)
A clump-forming, perennial herb; the tallest of the 4 white-flowered penstemons in Missouri. Flowers in loose terminal clusters; each flower 1¼ inches long, irregular, with 2 lips: the upper 2-lobed, the lower 3-lobed. Of the 5 stamens, 1 is modified into a hairy “tongue” and positioned centrally, probably to attract insects for pollination (hence the name "beard tongue"). Blooms May–July. Stem leaves opposite, lance-shaped, sessile (stalkless), with small, widely spaced teeth.