Kickxia elatine (L.) Dumort.
Family: Plantaginaceae
sharp-leaved cancerwort
Kickxia elatine image
from USDA Plants website  
Etymology: Kickxia: after Jean Kickx Jr. (1803-1864), and/or his father Jean Kickx (1775-1831); Belgian professors of botany
Plants: drooping or trailing annual, to 20" tall forb; stems not rooting
Leaves: triangular
Flowers: yellow, 5-parted, slender spur at the base, upper lip purple inside, stalks mostly smooth; solitary from the leaf axils
Conservation Status: Introduced - adventive