Bacopa is a genus of 70–100 aquatic plants belonging to the family Plantaginaceae. It is commonly known as waterhyssop (or water hyssop, though this is more misleading as Bacopa is not very closely related to hyssop but simply has a somewhat similar appearance).
They are annual or perennial, with decumbent or erect stems. The leaves are opposite or whorled, and sessile. The leaf blade is regular, round to linear, and the venation is palmate or pinnate. Its stems are hairy or smooth. The flowers are produced solitary or in pairs from leaf axils, usually radially symmetrical, with five sepals and five petals, and they are usually white, blue, or purple. Dispersal and propagation is by seeds and stem fragments. Crushed leaves have a distinctive ‘lemon’ scent.