Freshwater Algae Key

A1. Nonmotile algae without chloroplasts: Cyanobacteriophyta

A2. Motile algae with chloroplasts and flagella

A3. Nonmotile algae with chloroplasts but without flagella

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

B1. Cells rarely solitary; usually forming clumps or filaments

B2. Cells mostly solitary unless dividing

C1. Cells lack an obvious sinus; semi-cells usually separated by a simple suture that may not be visible

D1. Cells crescent-shaped, strongly or weakly curved, usually with tapered apices; cell wall lacking spines or teeth, but often striated; apex with vacuole containing one or more granules: Closterium

D2. Cells spherical, oval, or broadly elliptical, with no obvious sinus

D3. Cells elliptical, spindle-shaped, or cylindrical

C2. Cells with relatively distinct sinus; sinus may be open or closed, deep or shallow

A5. Cells enclosed in glassy, ornamental frustules: Diatoms