1 Capsule flattened, wider than long, notched; leaves dimorphic, with narrow submersed leaves on the lower stems, and broad floating leaves just subtending the aerial inflorescences; [of vernal pools on granite outcrops in Piedmont SC, GA, and AL]

1 Capsule turgid, longer than wide; leaves monomorphic; [collectively of many habitats and widespread].

  2 Flowers and fruits sessile or subsessile, the pedicels < 1 mm long; perennial.

    3 Leaves linear-subulate; corolla 2-3× as long as the calyx

    3 Leaves ovate; corolla 1-1.5 × as long as the calyx

  2 Flowers and fruits on definite pedicels; annual or perennial.

      4 Leaves clasping or subclasping-rounded at the base; perennial; [section Gratiola].

        5 Calyx subtended by 0 (-1) bractlet; corolla lobes white; corolla tube greenish yellow, conspicuously veined

        5 Calyx subtended by 2 bractlets; corolla lobes white or yellow-orange; corolla tube greenish yellow and conspicuously veined, or orange and not conspicuously veined.

          6 Corolla lobes and tube yellow-orange (very rarely white), not conspicuously veined; sepals and flower stalks sparsely or not at all glandular-puberulent

          6 Corolla lobes white to lavender, corolla tube greenish yellow, usually conspicuously veined; sepals and flower stalks densely glandular-puberulent.

             7 Leaves triangular to lanceolate, margins entire, or with a few teeth toward the tip; corolla veined with brown lines; sepals linear-lanceolate

               8 Leaves 3.5× as long as wide; lower leaf surface with only sunken, translucent glands

               8 Leaves < 3× as long as wide; lower leaf surface with large, yellow sessile glands and sunken, translucent glands

      4 Leaves cuneate at the base; annual; [section Nibora].

                 9 Corolla yellow; [LA and TX]

                 9 Corolla white (or with pink or purple flush); [collectively widespread].

                   10 Pedicels stout, erect, 1-5 (-12) mm long

                   10 Pedicels slender, spreading, 10-45 mm long.

                     11 Corolla 13-25 mm long; leaves oval or oblanceolate

                     11 Corolla 5-14 mm long; leaves elliptic, rhombic-lanceolate, or lanceolate

                       12 Mid-stem leaves (6-) 7-13 (-18) mm long; proximal fruiting pedicels (5-) 7-17 (-22) mm long, (0.9-) 1-2 (-2.3) × as long as the subtending bracteal leaves; bracteoles shorter than to barely exceeding the sepals; [of granite outcrops in the GA Piedmont]

                       12 Mid-stem leaves (11-) 20-41 (-66) mm long; proximal fruiting pedicels (8-) 13-25 (-37) mm long, (0.3-) 0.5-1 (-1.6) × as long as the subtending bracteal leaves; bracteoles slightly to conspicuously longer than the sepals; [collectively of more habitats and more widespread].

                          13 Leaves narrowly elliptic or rhombic to oblanceolate, not conspicuously falcate, (2.7-) 5-11 (-18) mm wide, (2.5-) 3.5-5 (-6)× as long as wide; leaf margins with (1-) 3-5 (-7) teeth per side; primary veins 3-5 (-7); mid-stem moderately to densely glandular pubescent (rarely glabrate); seeds (0.18-) 0.22-0.26 (-0.29) mm thick; [widespread]

                          13 Leaves linear, linear-lanceolate, to elliptic-lanceolate, often falcate, (1-) 2.5-4 (-4.5) mm wide, (5.5-) 6-9.5 (-11)× as long as wide; leaf margins with 0-2 (-3) teeth per side; primary veins 1 (-3); mid-stem glabrous; seeds (0.19-) 0.26-0.32 (-0.37) mm thick; [limestone cedar glades of n. AL and c. TN]