Freshwater Phytoplankton Keyfor the Northeast
By: Rachael Brown, Sonya Carlson, and Diana Jackson Under the guidance of Dr. Alan Baker
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Introduction:This photographic key is intended to aid in identification of freshwater algae to the Genus level. Proceed through this key by clicking on the picture that most resembles your organism.
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Cells with definite chloroplasts and nuclei, not blue-green in color
Cells without definite chloroplasts and nuclei, blue-green in color
Vegetative cells usually grass-green in color and with a definite cell wall
Vegetative cells not grass-green
Vegetative cells yellowish to brown with a glass-like silica wall of two
overlapping halves
Vegetative cells yellow-green with a cell wall
Rectangular
Is the general contour of the specimen:
Elongate strands of cells Oblong, Circular, or Globular
Sperm shaped
Note: A filament is a strand of cells arranged end to end
Filaments have elongate cells arranged end to
end
Filaments have horizontal cells that are stacked on top of each
other
Filaments Found Alone
Cells are round and are arranged in long
filaments (like strands of pearls)
Elongate unicells are found on a
substrate
unicells
Option A: Oblong
Cells float freely apart from each other
Cells join in even numbers and have a clear membrane
around them
Option B: Circular
Cells are free floating with thin clear membranes
Cells are congregated and encased in a round membrane
Is the shape of the organism rectangular?
Is the shape of the organism circular or oval?
Does organism have stalks?
Do the rectangles make a line or stairstep formation?
Do the rectangles form a star? Do the rectangles form a box?
Width (W) of individual cells is 1/10 of the length (L)
W
L
W
L
Width (W) of individual cells is 1/5 of the length (L)
Are there many small circles within the cells?
Is the end of the cell a long spike or is there a few large circles within the cells?
Is the middle of the cell wider than either end?
Is the end of the cell opposite of the stalk the
widest section?
Are there smaller circles within the large circle?
Are there lines around the edge of the circle?
Is the shape of the organism oval?
Is the cell extremely long and skinny with the length (L) more than 15 times as much the width (W)?
Is the cell extremely long and skinny with the length (L) more than 15 times as much the width (W)?
Are the ends of the cell pointed (p) or rounded (r) )?
Are the ends of the cell curved (c)? Are the ends of the cell flat (f)?
Is the cell the same width in the middle as it is nearer to the ends?
(a is equal to b)
Is the cell the wider in the middle than it is nearer to the ends?
(a is larger than b)
Is there a distinct line down the length of the cell?
DistinctLine
Is no distinct line visible in the center of the cell?
Is the center area of the middle line is wider than the ends of the middle line with a distinct
break in the center?
Is the middle line even in width with a distinct break in the
center? Is the middle line complete with no
distinct break in the center?
Is the cell long and skinny with the length (L) more than 5 times as much the
width (W)?
Is the cell short with the length (L) less than 5 times
as much the width (W)?
Are there distinct parallel lines extending from the middle of
the cell to the edge?
Is the interior of the cell a homogenous color without lines?
Lines
COLONIES (GROUPS OF CELLS)
FILAMENTS (LINEARLY)
CELLS ARE ARRANGED IN…
SINGLE CELLS
Class: Chlorophycae