Amphiroa rigida is an articulated, irregular, dichotomously branched, hard, calcified alga. Often, the dichotomous branching happens at the edge or in the middle of a joint. Even after the algae has dried off, the joints are sturdy and hold their shape. typically 2.5–6 cm in height. Pink in a variety of tones, from soft to bright. The algae turns white when it dries.