Introduction to Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 15

Table 1.5 Taxonomic and Morphological Diversity in Freshwater Blue-Green Algae.

Order: Major Morphotype Colony Size and Form Attached or Planktonic Examples

Chroococcales
(a) Unicellular to spheroid
colonies, lacking
specialised vegetative,
resistant or reproductive
cells

Single cells Planktonic or attached to

plant and substrate surfaces

Synechococcus (Fig. 4.31)

Small colonies (4-32
cells)

Free-floating, tangled-up with
ilamentous algae or
attached to substrates

Chroococcus (Fig. 4.33)
Gleocapsa (Fig. 4.32)

Flat plate of cells Free-floating or sedentary Merismopedia

Large solid spherical
colony

Planktonic Aphanocapsa (Fig. 4.35)

Microcystis (Fig. 4.34)

Large hollow spherical
colony

Planktonic Gomphosphaeria (Fig. 4.30)

Coelosphaerium

(b) Unicellular, forming
exospores

Cells remain single or
form multi-layered
colonies

Attached to surfaces of
aquatic plants, algae and
inorganic substrate

Chamaesiphon

Oscillatoriales
Filamentous algae, lacking
heterocysts and akinetes

Elongate straight
filaments.

Planktonic or benthic
Benthic mat

Oscillatoria (Fig. 4.27) a
Phormidium (Fig. 4.29)

Elongate spiral filaments Planktonic or on mud

surfaces

Spirulina (Fig. 4.26)

Nostocales
Filamentous algae forming
heterocysts and akinetes,
but no true branching

Bundles of Elongate
filaments.

Planktonic or benthic Aphanizomenon (Fig. 4.23)

Nostoc (Fig. 4.25)

3-D tangle of filaments Planktonic Anabaena (Fig. 4.24)

Spherical colony of
radiating filaments

Planktonic Gloeotrichia (Fig. 4.22)

Stigonematales
Filamentous algae forming
heterocysts and akinetes,
with true branching

Branched mass of
filaments.

Benthic or planktonic Stigonema (Fig. 4.20)

Differentiation into basal
filaments and erect
branches

Benthic Stauromatonema

Fischerella

a Planktonic species of Oscillatoria are placed in the genera Planktothrix , Pseudanabaena or Limnothrix by some authors.

classical (eukaryote) use of morphology to define
species is also problematic in this group, since the
species concept and definition of species are limited
by a complete absence of sexual reproduction.
In the absence of sexual processes, reproduction
in this group is by vegetative or specialised asexual
means. Asexual spores (akinetes) consist of vegeta-
tive cells that are larger than normal. They gener-
ally have thickened walls and, in filamentous forms,
are often produced next to heterocysts (Fig. 4.24 c).
Baeocysts (small spherical cells formed by division

of a mother cell) may be produced in some coc-
coid species and are released into the environment.
In some filamentous forms, deliberate fragmentation
of the filament can occur - releasing the fragments
(hormogonia) to produce new filaments.

1.3.3 Ecology

Blue-green algae are thought to have arisen approx-
imately 3.5 billion years ago (Schopf, 1993) dur-
ing which time they have been the dominant form