Characters: Colonies are corymbose plates with thick tapering branches. Branches have incipient axial corallites and branchlets developing towards their base. Sometimes branches are long. Axial corallites are rounded and not much larger than radial corallites. Radial corallites are irregular and have a wide range of shapes and sizes but are characteristically thick walled with rounded margins. Colour: Uniform grey, creamy brown, or purple. Similar species: Acropora polystoma, which has similar growth-forms and irregular corallites, but corallites are sharp edged, not rounded. See also A. austera, A. forskali, which has twisted branches and A. seriata, which has hhighly fused branches. Habitat: Shallow upper reef slopes exposed to strong wave action or currents. Abundance: Sometimes common on the Great Barrier Reef, usually uncommon elsewhere