It is a herbaceous annual, occasionally biennial or a short-lived perennial plant, growing to between 40-80 centimetres tall.
Each petal is deeply notched (Wenas Wildlife Area).
The appearance depends on the age of the plant; when young they form a basal rosette of oval to lanceolate leaves 4-10 cm long, and when they get older, forked stems grow from these, with leaves in opposite pairs. The flowers grow in clusters at the tops of the stems, 2.5-3 cm diameter, with a distinctive inflated calyx and five white petals, each petal deeply notched; flowering lasts from late spring to early autumn. The entire plant is densely hairy.