Cyanea st.-johnii, a member of the Campanulaceae (bellflower) family, is an unbranched shrub with a woody stem 30 to 60 cm (12 to 24 in) long. The leaves are lance-shaped to inversely lance-shaped, 6 to 13 cm (2.4 to 5.1 in) long and 1.5 to 2 cm (0.6 to 0.8 in) wide. The leaf edges are thickened, smoothly toothed, and curl under. The flowering stalk is 5 to 15 mm (0.2 to 0.6 in) long, with 5 to 20 flowers. The hairless, white petals, 3 to 6 cm (1.2 to 2.4 in) long, are suffused with pale violet in the inner surface.