Epiphyton and Renalcis , common components of lower and middle Paleozoic reefs, are end-members of a spectrum of diverse, micritic microfossils that often occur alongside or intergrown with each other. Five salient morphotypes are distinguished: dendritic (typified by Epiphyton ), septate, clotted, chambered, and saccate (the last three usually considered Renalcis ). Especially noteworthy among common intergrowths, intermediate forms, and cooccurrences are Epiphyton branches attached to Renalcis chambers. Such observations argue that these microfossils may not be deliberately precipitated skeletons of genetically distinct organisms. It is proposed that they represent precipitation of calcite, probably high-Mg, within colonies of coccoid blue-green algae in the environment of growth, soon after death of the algae. Entire "thalli" accreted apically by repeated growth and calcification of these colonies. The various forms, genera, and species resulted from size variation of colonies, frequency of calcification, and whether whole colonies or only their outer sheaths were replaced. Epiphyton and Renalcis are therefore "diagenetic taxa."