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

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

D1. Cells with toothed whorls or horn-like lateral extensions along entire lateral margin; cells narrowly or broadly cylindrical, with an indistinct sinus

D2. Cells circular, oval, or broadly elliptical in cross-section

D3. Cells moderately to strongly flattened in cross-section; cells circular, oval, or broadly elliptical in outline

D4. Cells biradiate, triradiate, or polyradiate (more than 3 angles) in cross-section, usually distinctly angular

A5. Cells enclosed in glassy, ornamental frustules: Diatoms