Freshwater Algae Key

A1. Nonmotile algae without chloroplasts: Cyanobacteriophyta

B1. Vegetative cells usually solitary

B2. Vegetative cells united into colonies or agglomerations

B3. Vegetative cells aligned end-to-end forming filaments or pseudofilaments

C1. Trichomes with heterocytes at one or both ends (basal) or along the trichome (intercalary)

C2. Trichomes lack heterocytes at all stages of development

D1. Trichomes are attached to aquatic plants (epiphytic), aquatic animals (epizoic), or found in mucilage surrounding algae, aquatic plants, or zooplankton (endogloeic)

D2. Trichomes are not epiphytic, epizoic, or endogloeic. This group contains many taxa that are difficult to identify correctly

E1. Trichomes are spiraling or coiled and usually highly motile: Arthrospira and Spirulina

E2. Multiple trichomes enclosed in a wide, common mucilage; live specimens actively motile: Microcoleus group (in part)

E3. Trichomes with fewer than 10 cells (usually 3); no visible sheath; cells compressed (W>L) with constricted cross-walls: Borzia

E4. Cell width considerably shorter than length; cells often coin-like

E5. Cells cubical, cylindrical, or oval; isodiametric (L=W) or slightly shorter or longer than wide (not coin-like)

A2. Motile algae with chloroplasts and flagella

A3. Nonmotile algae with chloroplasts but without flagella

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

A5. Cells enclosed in glassy, ornamental frustules: Diatoms