Lindernia dubia is an annual herb, 5- 20 cm tall, branching, stem often 4-sided.
Leaves opposite, to 3 cm long, oblong to elliptic, stalkless, tip blunt, base rounded, margin entire to remotely toothed.
Flowers pale bluish, bilaterally symmetrical, 0.5-1cm long, 2-lipped, upper lip 2-lobed, much narrower than 3-lobed lower lip, sepals narrow, 0.3-0.4 cm, fused at base, late season flowers often closed, self-pollinating, flowers in leaf axils, stalks shorter than leaves, open flowers visited by Halictid bees and other small bees, also by skippers and other small butterflies (Hilty 2006).
Fruit dry, a narrow, asymmetric capsule 0.4-0.6 cm long, with persistent style, ca 0.2 cm long (Radford et al. 1968), sitting amid old calyx lobes, splitting in two to release seeds; blooms and fruits June-Oct.
Wetland status: OBL.
Frequency in NYC: Infrequent.
Habitat: Open, disturbed wet roadsides, curbs, marshes or pond shores.