Cyanea magnicalyx is a shrub in the Campanulaceae (bellflower) family, 1.5 to 3 m (5 to 10 ft) tall; stems branched from base. Leaves elliptic, 36 to 55 cm (14 to 22 in) long, 19 to 27 cm (7.5 to 11 in) wide, margin pinnately cleft or parted toward apex and pinnately compound toward base; 9 or l0 per side. Unbranched inflorescence 6- to l5-flowered. Fused calyx lobes ovate, overlapping at base. Corolla yellowish white, longitudinally striped with purple, 6.5 to 7 cm (2.6 to 2.8 in) long, glabrous, with corolla tube laterally compressed. All 5 anthers with tufts of hairs 4 to 5 mm (0.16 to 0.2 in) long at apex, the surfaces glabrous; dorsal anthers 9.5 to 12 mm (0.4 to 0.5 in) long, 1/3 to 1/4 as long as the filament tube; ventral anthers 8 to 9 mm (0.3 to 0.35 in) long. Mature fruit and seeds not described.