Clasping Venus’ Looking Glass
Single-stemmed winter annual with 5-angled, somewhat hairy stems. Flowers tubular, surrounded by slender, 5-lobed calyx; emerge from leaf axils; star-shaped, about ½ inch across, blue-purple, rarely white. Blooms May-June. Leaves alternate, round, light green, clasping the stem, palmately veined, the margins finely and bluntly to sharply toothed, the undersurface finely roughened or with soft, short hairs.
Interestingly, the flowers on the lower parts of the stem are "cleistogamous": They remain closed and are self-fertilizing, setting seed without ever opening up. In this species, few of those seeds are viable, however. Flowers at the top of the stem are "chasmogamous": They open up and expose pistils and stamens to the air, inviting the possibility of cross-pollination.
Similar species: Five species of Triodanis occur in Missouri, as well as some hybrids that complicate their identification.