Three subfamilies of articulated coralline algae contain plants made up of holdfasts from which arise branching fronds of calcified intergenicula separated from one another by uncalcified genicula. The Corallinoideae contains a genus (Yamadaea) with extensive holdfasts and fronds of only one or two intergenicula, whereas most genera contain plants made up of hundreds of intergenicula. Primary branches arise at frond apices and secondary branches anywhere on intergenicular surfaces. For many years branching in articulated coralline algae has been described as dichotomous, pinnate, and in some taxa, palmate. The genicula in Metagoniolithon are more prominent than in other articulated coralline algae. Three species in one genus are placed in the subfamily Metagoniolithoideae. Several features characterize these plants: (1) many-celled genicula from which several branches arise, (2) mucilaginous caps surmounting the branch apices, (3) noncontiguous meristematic cells at the branch apices, and (4) the initially dichotomous branching of apices producing genicular tissue.