D. grandiflora is a perennial, evergreen plant which grows up to 1.5m, forming large clumps. The plant grows from underground rhizomes. The long, rigid, sword-shaped leaves, held in a fan shape, are dark green and may reach up to 1 m long and 15-20mm wide. The attractive flowers, held on erect slender stems about 1 m in length, are large (about 100 mm across) and are white with yellow nectar guides on the outer tepals and violet central segments. The fruit is a large capsule up to 45mm which is held erect and splits open to release shiny, dark brown seed.