Key to genera
1. Cells solitary, rarely aggregated into groups ...............................................................................................................2
- Cells forming various colonial aggregations .............................................................................................................. 3
2. Cells with lengthwise striated contents................................................................................................Cyanobacterium
- Cells with reticulate contents ......................................................................................................................Cyanothece
3. Cells in microscopic mucilaginous irregular colonies, at least partly in rows ............................................................4
- Cells within or on the surface of irregularly spherical colonies or in amorphous gelatinous colonies; not in rows....5
4. Colonies spherical or slightly elongated, with cells clustered in the centre and in short radiating rows at the colony periphery ......................................................................................................................................................Radiocystis
- Colonies irregularly-reticulate, composed of mucilaginous pseudofilamentous strands; cells not in radiating rows ........................................Cyanodictyon
5. Colonies containing small, conspicuous and variously shaped ferric precipitates, cells spherical or widely oval..... 6
- Colonies without ferric precipitates, cells oval or rod-shaped, colonies generally amorphous, cells oval or rod-shaped ......................................................7
6. Colonies irregularly spherical, loosely arranged within common mucilage, prominent granular ferric precipitates either within the centre of or on the colony surface...................................................................................Cyanogranis
- Colonies irregular with small ferric precipitates appearing as black ring-like or dot-like granules between adjacent cells or on the surface of cells....................................................................................................................Cyanocatena
7. Colonies with cells irregularly distributed throughout................................................................................................ 8
- Colonies with cells stratified or arranged in different densities in various parts of the colony (i.e. at or near the surface) ....................................................... 9
8. Cells irregularly arranged in colonies, without their own mucilaginous envelopes..................................Aphanothece
- Cells irregularly arranged in colonies, each with their own mucilaginous envelope, usually lamellate and often coloured .........................................Gloeothece
9. Cells situated on or near the surface of gelatinous colonies.......................................................................................10
- Cells situated on the ends of a system of pseudodichotomously branched mucilaginous stalks radiating from the centre of the colony....................Cyanonephron

10. Cells situated on the surface of irregularly spherical to elongated cylindrical to simply divicariate ............................Epigloeosphaera
- Cells situated in one layer under the surface of irregularly spherical colonies.................................Lemmermanniella