Lindernia dubia var. dubia  
Family: Linderniaceae
false pimpernel, moist bank pimpernel, yellow-seed false pimpernel
[Gratiola attenuata Spreng., Gratiola dubia L., Ilysanthes attenuata (Spreng.) Small, Ilysanthes dubia (L.) Barnhart, Ilysanthes gratioloides var. depressa Benth., Ilysanthes riparia Raf., Lindernia dubia var. major (L.) Pennell, Lindernia dubia var. riparia (L.) Pennell, Lindernia dubia var. typica (L.) Pennell, Lindernia procumbens auct. non (Krock.) Philcox, Lindernia pyxidaria var. major L.]
Lindernia dubia var. dubia image
from USDA Plants website  
Etymology: Lindernia: for Franz Balthasar von Lindern (1682-1755)
Plants: erect, annual, 2"-8" tall forb, branching
Leaves: opposite, mostly entire or with tiny teeth, lower leaves narrower to the base
Flowers: white to violet, 5-parted, 1/4" long, irregular shape, upper lip slightly 2-lobed and much narrower than somewhat backward pointing, 3-lobed lower lip; solitary from the leaf axils; blooms July-Sept.
Habitat: wet; shores; in sandy soil
Conservation Status: Native
Lindernia dubia var. dubia image
Lindernia dubia var. dubia image
Lindernia dubia var. dubia image
Lindernia dubia var. dubia image