Description from Flora of China
Gratiola dubia Linnaeus, Sp. Pl. 1: 17. 1753; G. anagallidea Michaux; Lindernia anagallidea (Michaux) Pennell; L. dubia var. anagallidea (Michaux) Cooperrider.
Annuals to 25 cm tall, diffuse, glabrous throughout except calyx. Stems purple, quadrangular, rooting at lower nodes, much branched. Leaves sessile, elliptic, 1-1.5 cm X 3-6 mm, decreasing in size upward, base rounded to cuneate, apex acute; veins 3-5, only primary vein conspicuous. Flowers axillary, solitary, in panicles. Pedicel slender, 1-2 cm. Calyx ca. 3 mm; lobes free to base, ca. 0.5 mm wide, hispidulous above, apex acuminate, obscurely 3-veined. Corolla white or pale blue, ca. 6.5 mm; lower lip 3-lobed; upper lip galeate, shallowly 2-lobed, lobes sharply pointed. Fertile stamens 2, posterior; staminodes 2, clavate, unappendaged, apex obtuse. Style ca. 3.5 mm. Capsule oblong, ca. 4 X 2.3 mm, rounded at both ends. Seeds ellipsoid.
Shallow water; low elevations. Guangdong, Taiwan [native to North America]