Diagnosis

Species with sturdy colonies, corymbose or digitate, secondary branching rare. Branches conical or terete. Axial corallites dominate the diameter of the branch, walls composed of a dense reticulum with three synapticular rings. Radial corallites short thickened tubular with dimidiate calices, evenly sized or in two sizes; coenosteum throughout reticulate with laterally flattened irregular spinules, sometimes reticulo-costate. Acropora humilis group is a paraphyletic group in which two main clades were recognized by Wallace (1999): A. humilis group 2 containing A. humilis and A. gemmifera, and the remaining paraphyletic species figured under the A. humilis group 1, including A. monticulosa, A. retusa, A. digitifera and A. samoensis. A similar grouping was later found by Wolstenholme et al. (2003), through an integrated morphological and genetic analysis on specimens from American Samoa: A. digitifera and A. monticulosa grouped together, while A. humilis and A. gemmifera formed a distinctive clade. This group is characteristic of the shallow parts of reefs on Pacific and Indian Ocean reefs, but not so common in the Indonesian archipelago. Specimens in the fossil record of Indonesia include A. monticulosa, A. samoensis and A. laurae sp. nov.