This is a variable species, widespread across North and South America; 2n = 18 and 32. Var. anagallidea is often considered somewhat distinct (see below), but colls. from BRAC (KNK), KENT (KNK) and perhaps elsewhere may be intermediate. Several colls. from Ky. have been referred to var. major Pennell (1935), but that taxon has not been recognized in subsequent treatments. Lindernia dubia is often confused with Gratiola neglecta; both grow in varied types of shoreline, ditches and drying pools. In addition to its pair of sterile stamens, lack of bracteoles (subtending calyx), and shorter calyx (F, Cr), L. dubia usually has glabrous stems (versus glandular-pubescent), leaves widest below the middle (versus at or above), a more diffusely branched sprawling habit, and later flowering (mostly Jul-Sep versus May-Jul), which often becomes cleistomagmous (versus all chasmagamous).