Freshwater Algae Key

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

B3. Nonmotile algae that form filaments or pseudofilaments

C1. Unbranched filamentous algae

D1. Cells very large; filaments coarse, unbranched, very sparsely branched; one genus lacks cellular crosswalls

D2. Cells spherical, lens-shaped, oval, or elliptical

D3. Cells cylindrical or narrowly elliptical

E1. Cells cylindrical, mostly longer than wide; some cells with ring-like cell division scars that resemble pipe threads: Oedogonium

E2. Cells cylindrical or oval, often paired; cell wall becoming increasinly thick and stratified, especially at crosswalls: Binuclearia

E3. Cells with H-shaped endwall extensions

E4. Cell wall without growth rings or H-shaped extensions

C2. Branched filamentous algae

A4. Cells with paired, symmetric semi-cells: Desmids

A5. Cells enclosed in glassy, ornamental frustules: Diatoms