"ceramium flaccidum" is a small branched red alga no more than 12 cm long. it grows in erect tufts of densely branched laterals. the filaments are basically monosiphonous, the axes are composed of large cells in series with cortical bands at the nodes. the cortication is of ascending and descending filaments which leave a bare internode. rhizoids are unicellular and numerous. the axes show strongly incurved tips. it has no spines unlike some other "ceramium" species.