A1. Nonmotile algae without chloroplasts: Cyanobacteriophyta
A2. Motile algae with chloroplasts and flagella
A3. Nonmotile algae with chloroplasts but without flagella
B1. Cells usually epiphytic, epizoic, or endozoic
B2. Nonmotile solitary and colonial algae; cells not (or usually not) epiphytic, epizoic, or endozoic
C1. Cells spherical, oval, or elliptical
C2. Cells not spherical, oval, or broadly elliptical
C3. Cells strongly angular, sometimes asymmetric or irregular in shape
B3. Nonmotile algae that form filaments or pseudofilaments
A4. Cells with paired, symmetric semi-cells: Desmids
A5. Cells enclosed in glassy, ornamental frustules: Diatoms