Brighamia rockii, a member of the Campanulaceae (bellflower) family, grows as an unbranched plant 1 to 5 m (3.3 to 16 ft) tall with a thickend, succulent stem that tapers from the base. The fleshy, oval leaves are widest at their tips and are arranged in a rosette at the top of the plant, 6 to 22 cm (2.4 to 8.7 in) long and 5 to 15 cm (2 to 6 in) wide. The fragrant flowers are clustered in groups of three to eight in the leaf axils (the point between the leaf and the stem). Each flower cluster is on a stalk 3.5 to 7.5 cm (1.4 to 3 in) long, and each flower is on a stalk 6 to 12 mm (0.2 to 0.5 in) long. The green basal portion of the flower (hypanthium) has 10 ribs and is topped by 5 calyx lobes 2.5 to 8 mm (0.01 to 0.3 in) long. The petals are fused into a green to yellowish-green tube 8 to 13 cm (3 to 5 in) long and 0.2 to 0.4 cm (0.1 to 0.2 in) wide which flares into five white, elliptic lobes 1.7 to 3.7 cm (0.7 to 1.5 in) long and 0.8 to 1.3 cm (0.3 to 0.5 in) wide. The fruit is a capsule 13 to 20 mm (0.5 to 0.8 in) long, 7 to 10 mm (0.3 to 0.4 in) wide, and 3 to 4 mm (0.1 to 0.2 in) thick which contains numerous seeds about 1 mm (0.05 in) long.