Cell Chlorophyll Pigments Membranes Thylakoids Storage Covering Flagella
Prokaryotic a Phycocyanin, Allophycocyanin No chloroplast No chloroplast starch, granules, polyhedral bodies murein and polysaccharides None

Public Domain Public Domain Wikimedia Commons. Anabaena_sperica.jpeg


Cyanobacteria, or blue-green algae, are a group of prokaryotic, photosynthetic organisms.

Cyanobacteria are considered a primitive form of life because were an early, and likely the earliest, form of life on earth. The cells of blue-green algae are called prokaryotic cells (from Greek “pro” for “before” and “karyon” referring to the “nut” or nucleus). The cells are small, and require a microscope to observe their structures. Individual cells, however, may form colonies that are visible to the naked eye.

Cyanobacteria are photosynthetic, that is, they use energy from the sun (photosynthesis) to make sugars inside the cell. They were not only the earliest organisms on earth, they are responsible for changing the composition of the atmosphere. When cyanobacteria evolved a couple of billion years ago, there was no oxygen in the atmosphere. Gradually, over time, the oxygen released through photosynthesis created the atmosphere that we have today. These tiny organisms also affect the global cycle of nitrogen. Cyanobacteria are one of a small group of organisms, which are able to “fix” nitrogen and are very important in the global nitrogen cycle. They fix 28 teragrams or 6.17 x 1010 pounds (equal to almost 7 million elephants) of nitrogen per year just in the ocean. There are other nitrogen fixers in freshwaters, as well. As compared to the other algal divisions, many of the cyanobacteria are able to live in extreme environments. For example, some species of cyanobacteria are able to live in hot springs, where temperatures reach to 72°C (176°F). They also live in hypersaline (high salt concentrations) habitats of marine tidal areas.


Cells range in size from less than 1 micron to about 40 microns. Note that a micron is 0.001 meters. For comparison, the human hair is about 90 microns in width. Unlike the eukaryotic algae, with a membrane-bound nucleus, the cyanobacteria lack a membrane around the cell nucleus. Cyanobacteria are found in a large variety of forms, or with a range of morphologic features. Cells may grow alone (unicellular) and or in colonies (such as filaments, spherical balls, branching filaments, and sheets of cells). Five morphological groups have been established, shown in Table 1. Some species of cyanobacteria have specialized cells, called heterocysts, that absorb nitrogen from the atmosphere (as N2) and convert it to ammonia, which can be used by other organisms.

Cyanobacteria groups:

I. Unicellular: single cells or cell aggregates. Gloeothece, Gloeobacter, Synechococcus, Cyanothece, Gloeocapsa, Synechocystis, Chamaesiphon, Merismopedia

II. Pleurocapsalean: reproduce by formation of small spherical cells called baeocytes produced through multiple fission. Dermocarpa, Xenococcus, Dermocarpella, Pleurocapsa, Myxosarcina, Chroococcidiopsis

III. Oscillatorian: filamentous cells that divide by binary fission in a single plane. Oscillatoria, Spirulina, Arthrospira, Lyngbya, Microcoleus, Pseudanabaena

IV. Nostocalean: filamentous cells that produce heterocysts Anabaena, Nostoc, Calothrix, Nodularia, Cylinodrosperum, Scytonema

V. Branching: cells divide to form branches Fischerella, Stignoema, Chlorogloeopsis, Hapalosiphon

Blue-green algae in Rocky Mountain Lakes

In the Rocky Mountains, cyanobacteria live in nearly every type of environment that contains even a small amount of water – cyanobacteria are found in lakes, streams, soil, even growing within small spaces on the surfaces of rocks. In montane and alpine lakes, a number of genera, such as Aphanothece and Chroococcus grow in the plankton (from Greek for “wanderer” or “drifter”). The phytoplankton are those organisms that photosynthesize and are carried by currents in the water; they are not able to move on their own. Genera such as Nostoc are able to fix nitrogen by forming heterocysts. Genera such as Lyngbya and Oscillatoria form filaments that grow on the bottom of lakes, or may be carried by water currents in the plankton.

44 taxa shown below, 39 of which appear in at least one sample.

Name Basionym Synonyms Lakes Samples Region* ID
Anabaena sp. 2 6 RMNP, 5001
Anabaena spiroides 0 0 5002
Aphanocapsa delicatissima 3 5 RMNP, 5003
Aphanotheca sp. 1 9 RMNP, 5004
Aphanothece clathrata 0 0 5005
Aphanothece minutissima 0 0 5006
Aphanothece sp. 6 21 RMNP, 5007
Chroococcus dispersus 4 60 RMNP, 5036
Chroococcus limneticus 2 34 RMNP, 5008
Chroococcus sp. 3 22 RMNP, 5009
Chroococcus turgidus 1 1 RMNP, 5037
Chroococcus varius 1 1 RMNP, 5010
Cyanophyte sp. 1 174 SLW, 5035
Dactylococcopsis acicularis 2 3 RMNP, 5011
Dactylococcopsis fasciculatus 2 21 RMNP, 5012
Dactylococcopsis sp. 2 5 RMNP, 5013
Gloeothece sp. 1 1 RMNP, 5014
Lyngbya (Leptolygnbya) nana 1 1 RMNP, 5015
Lyngbya limnetica 5 9 RMNP, 5016
Lyngbya nana 2 10 RMNP, 5017
Lyngbya sp. 1 1 RMNP, 5018
Merismopedia sp. 1 3 RMNP, 5019
Microcystis sp. 1 2 RMNP, 5020
Nostoc paludosum 1 1 RMNP, 5021
Nostoc sp. 1 1 RMNP, 5022
Oscillatoria augusta 1 2 RMNP, 5038
Oscillatoria augustissima 1 3 RMNP, 5023
Oscillatoria limnetica 3 96 RMNP, 5024
Oscillatoria sp. 2 14 RMNP, 5025
Oscillatoria sp. 1 1 2 RMNP, 5039
Oscillatoria sp. 2 1 1 RMNP, 5040
Oscillatoria subbrevis f. minor 0 0 5044
Phormidium sp. 1 7 RMNP, 5026
Planktolygnbya subtilis (Lyngbya limnetica) 0 0 5027
Rhabdoderma sigmoidea 1 3 RMNP, 5028
Rhabdoderma sp. 1 122 SLW, 5029
small blue-green filament 2 3 RMNP, 5041
Symplocastrum sp. 1 1 RMNP, 5042
Synechococcus elongatus 2 10 RMNP, 5030
Synechococcus irregulare 1 1 RMNP, 5043
Synechococcus linearis 2 12 RMNP, 5031
Synechococcus sp. 1 4 RMNP, 5032
Synechocystis sp. 2 2 RMNP, 5033
Tetrarcus ilsteri 1 1 RMNP, 5034

RMNP = Rocky Mountain National Park, CO
SLW = Silver Lakes Watershed, CO