A1. NONMOTILE ALGAE WITHOUT CHLOROPLASTS: CYANOBACTERIA
A2. NONMOTILE ALGAE WITH CHLOROPLASTS
A3. MOTILE ALGAE WITH CHLOROPLASTS AND FLAGELLA
B1. MOTILE COLONIES WITH TWO OR MORE CELLS
C1. CELLS WITH TWO EQUAL FLAGELLA
D1. FLAT COLONIES WITH 4-16 SPHERICAL OR OVAL CELLS: Gonium and Tetrabaena
D2. SPHERICAL, OVAL, OR ELLIPTICAL COLONIES (NOT FLAT)
C2. CELLS WITH TWO DISSIMILAR FLAGELLA
B2. MOTILE SINGLE-CELL ALGAE
A4. CELLS DIVIDED INTO MIRROR-IMAGE SEMI-CELLS: Desmids (see key at cedar.wwu.edu/cedarbooks/14/ )
A5. CELLS ENCLOSED IN GLASSY, ORNAMENTAL FRUSTULES: Diatoms (see key at diatoms.org)