It is an annual herb with a stout main root and fibrous lateral roots. The stem is slender, purplish-green, 12-32 cm tall, tetragonal, and sparsely hairy. Leaves vary from pinnate compound below to simple above, with serrate margins.
7-9月
Var. erythrophylla often has larger leaves mostly basal, usually pinnate compound with 1-2 pairs of leaflets, occasionally simple, with serrate margins. The undersides are purple and both surfaces are sparsely to nearly hairless.
The flowers are purple or purplish-red, with a corolla tube extending slightly beyond the calyx, lips 3-lobed with the middle lobe inverted-heart shaped and side lobes ovate-triangular.