A1. Nonmotile algae without chloroplasts: Cyanobacteriophyta
B1. Vegetative cells usually solitary
B2. Vegetative cells united into colonies or agglomerations
C1. Cells arranged in a single layer to form flat colonies
C2. Colonies comprised of cubical, four-cell subgroups
C3. Colonies approximately spherical
C4. Cells arranged into irregular, amorphous colonies
D1. Cells appear brown and mottled under microscope
E1. Cells spherical or oval; distributed througout colony (not forming single layer around hollow colony center): Microcystis
E2. Cells arranged in single layer on outer perimeter of a hollow colony: Woronichinia naegeliana
E3. Spherical or hemispherical colony comprised of filaments radiating from common center: Gloeotrichia
D2. Cells various colors but not mottled brown when viewed under the microscope
B3. Vegetative cells aligned end-to-end forming filaments or pseudofilaments
A2. Nonmotile algae with chloroplasts
A3. Motile algae with chloroplasts and flagella
A4. Cells divided into paired semi-cells that are approximate mirror images of each other: Desmids
A5. Cells enclosed in glassy, ornamental frustules; many species exhibit gliding movement: Diatoms