Acropora aculeus forms corymbose, pillow-like structures, the horizontal branches being slender and spreading while the upright branches are narrow and shorter. The corallites are distinctive, longer than they are wide, smooth and polished. This coral is usually yellowish or grey, but can be bright bluish-green, and the tips of the branches are often yellow, pale blue, green or brown. It is usually yellow on the Great Barrier Reef and in the Philippines, but pale brown in western Australia. It is named as ACR ACUL in Coral Codes.
