Annual, spreading by seed but late germinated plants may overwinter and the spreading stems take root at nodes. Seeds usually remain viable in the soil for 4 to 6 years, but some have been recovered after about 20 years, which germinated. Not a particularly
invasive weed. A small amount of sweet nectar can be
sucked from the base of the flower. The young leaves can be added to salads or stir-fried, but the flavour is not great.
The dark green, hairy leaves have a scalloped edge, and a dull appearance. They are attached to the square stems with a short petiole in opposing pairs. The upper leaves can have a purplish tinge.
The purple-red flowers occur in whorls at the top of the stems from April to October.
Hoe or hand pull, it is easily uprooted and the fibrous roots do not regrow provided the basal growing point is removed. In wet weather shoot fragments may take root if partially buried.