Freshwater Algae Key

A1. NONMOTILE ALGAE WITHOUT CHLOROPLASTS: CYANOBACTERIA

A2. NONMOTILE ALGAE WITH CHLOROPLASTS

B1. CELLS USUALLY SOLITARY

C1. CELLS ENCLOSED IN RIGID LORICA, TEST, OR THICK WALLED CYST

C2. CELLS SPHERICAL, OVAL, ELLIPTICAL, OR LEMON-SHAPED IN OUTLINE

D1. CELLS SPHERICAL OR NEARLY SPHERICAL; CELL WALL MAY BE THICK BUT CELLS ARE NOT SURROUNDED BY VISIBLE MUCILAGE LAYER

D2. CELLS SPHERICAL OR NEARLY SPHERICAL (BROADLY OVAL) IN OUTLINE AND SURROUNDED BY MUCILAGE LAYER

E1. CELLS SPHERICAL, GOLDEN BROWN, SOLITARY OR PAIRED; SURROUNDED BY STRIATED MUCILAGE: Gloeodinium

E2. CELLS SPHERICAL, YELLOWISH GREEN, WITH RED PIGMENT DROPLET; SOLITARY OR IN SMALL COLONIES SURROUNDED BY DIFFUSE BUT (USUALLY) VISIBLE MUCILAGE: Chlorobotrys

E3. SPHERICAL OR OVAL, BRIGHT GREEN CELLS WITH STAR-SHAPED CHLOROPLAST RADIATING FROM CENTRAL PYRENOID; SOLITARY OR IN SMALL COLONIES SURROUNDED BY DIFFUSE BUT (USUALLY) VISIBLE MUCILAGE: Asterococcus

E4. SPHERICAL OR NEARLY SPHERICAL, BRIGHT GREEN CELLS WITH DENSE (NOT STAR-SHAPED) CHLOROPLAST; SOLITARY OR IN SMALL COLONIES SURROUNDED BY NARROW MUCILAGE LAYER: Planktosphaeria

E5. SPHERICAL OR NEARLY SPHERICAL, DULL OR BRIGHT GREEN CELLS WITH DENSE (NOT STAR-SHAPED) CHLOROPLAST; SOLITARY OR IN SMALL TO LARGE SIZED COLONIES; CELLS MAY OR MAY NOT BE SURROUNDED BY MUCILAGE; COLONIES USUALLY SURROUNDED BY DIFFUSE MUCILAGE: Sphaerocystis

D3. CELLS OVAL, ELLIPTICAL, OR LEMON-SHAPED; CELL MAY OR MAY NOT BE SURROUNDED BY MUCILAGE; ALSO CHECK SPHERICAL SECTION FOR BROADLY OVAL CELLS

C3. CELLS CLUB-SHAPED, CRESCENT-SHAPED, ELLIPTICAL, OR FUSIFORM IN OUTLINE

C4. CELLS ANGULAR IN OUTLINE WITH THREE OR MORE SIDES

B2. NONMOTILE COLONIES WITH TWO OR MORE CELLS

B3. FILAMENTOUS ALGAE (INCLUDING PSEUDOFILAMENTS)

B4. CELLS ATTACHED TO ZOOPLANKTON (EPIZOIC), LIVING INSIDE ZOOPLANKTON OR OTHER AQUATIC ANIMALS (ENDOZOIC), OR ATTACHED TO AQUATIC PLANTS (EPIPHYTIC)

A3. MOTILE ALGAE WITH CHLOROPLASTS AND FLAGELLA

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)