Small, multi-stemmed tree with a dense, rounded crown, 3-8 m high with arching branches, sometimes touching the ground. The bark is pale grey and smooth and the branchlets appear knobbly due to persistent leaf-like appendages at the base of the leaf stalk (stipules). The glossy, green leaves are usually in groups of three and crowded at the end of short branches. The leaves are spoon-shaped with a broadly rounded tip and a tapering base. They have small pockets of hair in some axils of veins (domatia) and a wavy margin. The flowers are solitary, large (up to 100 mm in diameter), and showy with a sweet scent. The trumpet-like flowers are white turning yellow with age, with a long tube that opens up into 6-9 lobes. The flowers open during the night and are probably moth-pollinated.

The flowering season ranges from July to December (winter to summer) and the fruits ripen between December and April (summer to autumn), but may remain on the tree until August. The fruit is almost round, shallowly to strongly ribbed longitudinally, greyish green to white with white, slightly raised dots (lenticels). The fruit contains numerous seeds embedded in pulp.

Two subspecies occur in southern Africa. They are distinguished on fruit characters but this is not always possible, especially in the case of herbarium specimens. Gardenia volkensii subsp. volkensii differs from subsp. spatulifolia by the larger, white fruit with coarser ribs and conspicuous white dots (lenticels). G. volkensii subsp. volkensii var. saundersiae has a calyx with well-developed lobes (15-25 mm long) while G. volkensii subsp. volkensii var. volkensii has calyx lobes up to 10-15 mm long.