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

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

E1. CELLS OVAL OR ELLIPTICAL, WITH LONG SETAE OR SPINES; SOLITARY OR IN SMALL COLONIES ENCLOSED IN OLD PARENT CELL WALL: Lagerheimia

E2. CELLS BROADLY OVAL; SOLITARY OR IN SMALL COLONIES ENCLOSED IN GELATINIZED PARENT CELL WALL: Oonephris

E3. CELLS OVAL, ELLIPTICAL, OR LEMON-SHAPED; SOLITARY OR IN SMALL COLONIES ENCLOSED IN EXPANDED PARENT CELL WALL: Oocystis

E4. CELLS OVAL OR ELLIPTICAL AND BRIGHT BLUE-GREEN; SOLITARY OR IN SMALL COLONIES ENCLOSED IN OLD PARENT CELL WALL: Glaucocystis

E5. 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

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)