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.
==Useful parts of the plant==
*'''Root, Stem and Leaves'''.
== Uses ==