A genus of about 170 species, herbs, cosmopolitan. The key is adapted in part from Brashier (1966), Faden (1993), and Tucker (1989).
ID notes: Commelina has bilateral flowers, with 2 large petals (usually blue or white, but peach-colored in one species) and 1 smaller petal (often paler, and sometimes translucent). The flowers emerge from a folded spathe (very different than the leaves) which is heart-shaped if opened and spread. Only Tinantia (restricted to TX) is similar in these features; it differs in having 6 rather then 3) fertile stamens, and the filaments being bearded with hairs (rather than glabrous).