This annual is widespread in eastern states on dry infertile acid soils. Among Ky. species of Agalinis (Pennell 1935), tenuifolia is unique in having upper corolla lobes that project forward over stamens and style (versus reflexed-spreading), and the inner surface of its corolla is largely glabrous (versus pubescent at least in part). Inflorescences have relatiely dense racemose branches, with relatively short pedicels that are often curved upwards. Further study of variation is needed; see notes under var. macrophylla. Reports of the more western var. parviflora (Nutt.) Pennell from Ky. are probably erroneous (M). Reports of the more southeastern relative, A. setacea (J.F. Gmel.) Raf., are probably based on misidentified tenuifolia (M).