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Freshwater algae
Freshwater algae identification guide
List of taxa included in this guide
Scroll to
Cryptophytes
Cyanobacteria
Diatoms
Dinoflagellates
Euglenoids
Golden-brown algae
Green algae
Red algae
Sewage fungus
Yellow-green algae
Cryptophytes
Cryptomonas
(Cryptomonadaceae)
Cell with rigid cell wall and motile
Factsheet
Cyanobacteria
Ammatoidea
(Homoeotrichaceae)
Tapering to fine, colourless hairs
Factsheet
Anabaena
(Nostocaceae)
Filaments composed of regular cells occasionally interrupted by specialised cells
Factsheet
Aphanocapsa
(Merismopediaceae)
Cells small, irregularly dispersed in homogenous jelly
Factsheet
Aphanothece
(Synechococcaceae)
Cells small, irregularly dispersed in homogenous jelly
Factsheet
Calothrix
(Rivulariaceae)
Filament contains heterocytes
Factsheet
Chamaesiphon
(Chamaesiphonaceae)
Blue-green, grey, whitish or reddish - no organelles
Factsheet
Chroococcus
(Chroococcaceae)
Cells lack organelles
Factsheet
Coleodesmium
(Microchaetaceae)
Filament contains heterocytes
Factsheet
Cyanothece
(Synechococcaceae)
Cell wall is smooth and featureless
Factsheet
Dichothrix
(Rivulariaceae)
Filament contains heterocytes
Factsheet
Gloeocapsa
(Microcystaceae)
Cells lack organelles
Factsheet
Homoeothrix
(Homoeotrichaceae)
Filaments do not contain heterocytes
Factsheet
Hormoscilla
(Oscillatoriaceae)
Cells shorter than wide
Factsheet
Lyngbya
(Oscillatoriaceae)
Cells shorter than wide
Factsheet
Merismopedia
(Merismopediaceae)
Cells lack organelles
Factsheet
Microcoleus
(Phormidiaceae)
Fine colourless hairs absent
Factsheet
Microcystis
(Microcystaceae)
Cells small, irregularly dispersed in homogenous jelly
Factsheet
Nostoc
(Nostocaceae)
Filaments composed of regular cells occasionally interrupted by specialised cells
Factsheet
Oscillatoria
(Oscillatoriaceae)
Cells shorter than wide
Factsheet
Phormidium
(Phormidiaceae)
Most cells are as long as or longer than wide
Factsheet
Placoma
(Hydrococcaceae)
Cells lack organelles
Factsheet
Pseudanabaena
(Pseudanabaenaceae)
Most cells are as long as or longer than wide
Factsheet
Rivularia
(Rivulariaceae)
Filament contains heterocytes
Factsheet
Schizothrix
(Schizotrichaceae)
Filaments do not contain heterocytes
Factsheet
Scytonema
(Scytonemataceae)
Filament contains heterocytes
Factsheet
Spirulina/Arthrospira
(Phormidiaceae)
Filaments are worm-like
Factsheet
Stigonema
(Stigonemataceae)
Branch points roughly equal
Factsheet
Tolypothrix
(Microchaetaceae)
Filament contains heterocytes
Factsheet
Wilmottia
(Phormidiaceae)
Most cells are as long as or longer than wide
Factsheet
Xenococcus
(Xenococcaceae)
Cells lack organelles
Factsheet
Diatoms
Achnanthes cf inflata
(Achnanthaceae)
Chloroplasts visible inside cells are brown
Factsheet
Achnanthidium
(Achnanthidiaceae)
Central raphe
Factsheet
Asterionella cf. formosa
(Fragilariaceae)
Raphe absent
Factsheet
Aulacoseira granulata
(Aulacoseiraceae)
Chloroplasts visible inside cells are brown
Factsheet
Cerataulina
(Hemiaulaceae)
Chloroplasts visible inside cells are brown
Factsheet
Cocconeis placentula
(Cocconeidaceae)
Central raphe
Factsheet
Craticula
(Stauroneidaceae)
Central raphe
Factsheet
Cyclotella cf stelligera
(Stephanodiscaceae)
Circular
Factsheet
Cymbella
(Cymbellaceae)
Rotational symmetry of cell face outline is 360 degrees; one end is a reflection of the other
Factsheet
Diatoma
(Fragilariaceae)
Chloroplasts visible inside cells are brown
Factsheet
Didymosphenia
(Gomphonemataceae)
Rotational symmetry of cell face outline is 360 degrees with one end broader than other
Factsheet
Diploneis cf elliptica
(Diploneidaceae)
Central raphe
Factsheet
Encyonema
(Cymbellaceae)
Rotational symmetry of cell face outline is 360 degrees; one end is a reflection of the other
Factsheet
Eolimna
(Naviculaceae)
Central raphe
Factsheet
Epithemia
(Rhopalodiaceae)
Rotational symmetry of cell face outline is 360 degrees; one end is a reflection of the other
Factsheet
Eunotia
and relatives (Eunotiaceae)
Rotational symmetry of cell face outline is 360 degrees; one end is a reflection of the other
Factsheet
Fistulifera
(Naviculaceae)
Central raphe
Factsheet
Fragilaria
(Fragilariaceae)
Chloroplasts visible inside cells are brown
Factsheet
Frustulia
(Amphipleuraceae)
Central raphe
Factsheet
Gomphoneis
(Gomphonemataceae)
Rotational symmetry of cell face outline is 360 degrees with one end broader than other
Factsheet
Gomphoneis
(Gomphonemataceae)
Cells are joined by long stalks made of jelly
Factsheet
Gyrosigma
(Pleurosigmataceae)
Rotational symmetry of cell face outline 180 degrees, with the ends being opposite reflections of each other
Factsheet
Hantzschia
(Bacillariaceae)
Rotational symmetry of cell face outline is 360 degrees; one end is a reflection of the other
Factsheet
Melosira varians
(Melosiraceae)
Chloroplasts visible inside cells are brown
Factsheet
Meridion cf circulare
(Fragilariaceae)
Rotational symmetry of cell face outline is 360 degrees with one end broader than other
Factsheet
Naviculoid diatoms (Naviculaceae)
Central raphe
Factsheet
Nitzschia
(Bacillariaceae)
Rotational symmetry of cell face outline 180 degrees, with the ends being opposite reflections of each other
Factsheet
Pinnularia
(Pinnulariaceae)
Central raphe
Factsheet
Planothidium
(Achnanthidiaceae)
Central raphe
Factsheet
Rhoicosphenia cf curvata
(Rhoicospheniaceae)
Central raphe
Factsheet
Rhopalodia
(Rhopalodiaceae)
Rotational symmetry of cell face outline is 360 degrees; one end is a reflection of the other
Factsheet
Sellaphora
(Sellaphoraceae)
Central raphe
Factsheet
Stauroneis cf anceps
(Stauroneidaceae)
Central raphe
Factsheet
Staurosira
(Fragilariaceae)
Raphe absent
Factsheet
Surirella
(Surirellaceae)
Raphe on edge of cell
Factsheet
Tabellaria flocculosa
(Tabellariaceae)
Chloroplasts visible inside cells are brown
Factsheet
Ulnaria
(Fragilariaceae)
Raphe absent
Factsheet
Dinoflagellates
Ceratium
(Ceratiidae)
Cell wall ornamented with spines
Factsheet
Gymnodinium
(Gymnodiniidae)
Shallow groove encircles the cell equator
Factsheet
Peridinium
(Peridiniidae)
Cell wall ornamented with spines
Factsheet
Euglenoids
Euglena
(Euglenidae)
Unicellular
Factsheet
Phacus
(Euglenidae)
Cell with rigid cell wall and motile
Factsheet
Trachelomonas
(Euglenidae)
Cell with rigid cell wall and motile
Factsheet
Golden-brown algae
Chrysocapsa
(Chrysocapsaceae)
Cell contents (chloroplasts) are brown or golden-brown
Factsheet
Dinobryon
(Dinobryaceae)
Cell contents (chloroplasts) are brown or golden-brown
Factsheet
Synura
(Synuraceae)
Cell contents (chloroplasts) are brown or golden-brown
Factsheet
Green algae
Actinastrum
(Radiococcaceae)
Cells long and thin, with tapering ends
Factsheet
Ankistrodesmus
(Radiococcaceae)
Cell outline long and thin
Factsheet
Arthrodesmus
(Desmidiaceae)
Cell outline has a deep constriction
Factsheet
Bracteacoccus
(Chlorococcaceae)
Cells containing membrane-bound organelles
Factsheet
Chaetophora
(Chaetophoraceae)
Filaments are one cell wide
Factsheet
Chara
(Characeae)
Structured as a main axis with whorls of branches at nodes
Factsheet
Characium
(Chlorococcaceae)
Cell outline elongated with basal holdfast
Factsheet
Chlamydomonas
(Chlamydomonadaceae)
Cell with rigid cell wall and motile
Factsheet
Chlorella
- like unicells (Chlorellaceae)
Cells containing membrane-bound organelles
Factsheet
Chlorogonium
(Chlamydomonadaceae)
Cell with rigid cell wall and motile
Factsheet
Chodatella
(Oocystaceae)
Cell wall ornamented with spines
Factsheet
Cladophora glomerata
(Cladophoraceae)
Filaments are one cell wide
Factsheet
Closteriopsis
(Oocystaceae)
Cell outline long and thin
Factsheet
Closterium
(Closteriaceae)
Cell outline crescent-shaped
Factsheet
Coccomyxa/Pseudococcomyxa
(Oocystaceae)
Cells containing membrane-bound organelles
Factsheet
Coelastrum
(Radiococcaceae)
Colonies have regular structure
Factsheet
Coleochaete
(Coleochaetaceae)
Colony comprised of cells in flat sheets or skeins; cells lack contrictions
Factsheet
Cosmarium
(Desmidiaceae)
Cell outline has a deep constriction
Factsheet
Cylindrocystis
(Mesotaeniaceae)
Cells containing membrane-bound organelles
Factsheet
Desmidium
(Desmidiaceae)
Cells have constrictions between them
Factsheet
Desmodesmus
(Radiococcaceae)
Cells ellipsoidal
Factsheet
Diacanthos
(Oocystaceae)
Cell wall ornamented with spines
Factsheet
Dictyosphaerium
(Dictyosphaeraceae)
Cells connected by branching threads
Factsheet
Dimorphococcus
(Dictyosphaeraceae)
Cells connected by branching threads
Factsheet
Draparnaldia
(Chaetophoraceae)
Branch are markedly unequal
Factsheet
Elliptochloris
(Prasiolales incertae sedis)
Cells containing membrane-bound organelles
Factsheet
Euastrum
(Desmidiaceae)
Cell outline has a deep constriction
Factsheet
Eudorina
(Volvocaceae)
Cells embedded in a mass of spherical jelly
Factsheet
Golenkinia
(Micractiniaceae)
Cell wall ornamented with spines
Factsheet
Haematococcus
(Chlamydomonadaceae)
Cell with rigid cell wall and motile
Factsheet
Hyalotheca
(Desmidiaceae)
Cells have constrictions between them
Factsheet
Interfilum paradoxum
(Klebsormidiaceae)
Cells containing membrane-bound organelles
Factsheet
Kirchneriella
(Oocystaceae)
Cell outline crescent-shaped
Factsheet
Klebsormidium
(Klebsormidiaceae)
Cell wall is smooth and featureless
Factsheet
Micractinium / Errerella
(Micractiniaceae)
Colony is a tight mass of cells with long spines radiating outward
Factsheet
Micrasterias
(Desmidiaceae)
Cell outline has a deep constriction
Factsheet
Microspora
(Microsporaceae)
Cell walls composed of overlapping pieces
Factsheet
Microthamnion
(Microthamniaceae)
Branch points roughly equal
Factsheet
Monostroma
(Monostromataceae)
Colony comprised of cells in flat sheets or skeins; cells lack contrictions
Factsheet
Mougeotia
(Zygnemataceae)
Cell wall is smooth and featureless
Factsheet
Nitella
(Characeae)
Structured as a main axis with whorls of branches at nodes
Factsheet
Oedogonium
(Oedogoniaceae)
Chloroplasts visible inside cells are green or yellow-green
Factsheet
Oocystis
(Oocystaceae)
Cells containing membrane-bound organelles
Factsheet
Pandorina
(Volvocaceae)
Cells embedded in a mass of spherical jelly
Factsheet
Parallela
(Palmellaceae)
Colony comprised of cells in flat sheets or skeins; cells lack contrictions
Factsheet
Pediastrum
(Hydrodictyaceae)
Colonies have regular structure
Factsheet
Pleurotaenium
(Desmidiaceae)
Cell outline has a deep constriction
Factsheet
Polyedriopsis
(Chlorococcaceae)
Cell wall ornamented with spines
Factsheet
Quadrigula
(Oocystaceae)
Cells long and thin, with tapering ends
Factsheet
Rhizoclonium
(Cladophoraceae)
Cell wall is smooth and featureless
Factsheet
Red algae
Audouinella hermanii
(Acrochaetiaceae)
Filaments are one cell wide
Factsheet
Batrachospermum
(Batrachospermaceae)
Branch are markedly unequal
Factsheet
Bostrychia
(Rhodomelaceae)
Filaments more than one cell wide
Factsheet
Caloglossa
(Delesseriaceae)
Filaments more than one cell wide
Factsheet
Chroodactylon
(Stylonemataceae)
Filaments are one cell wide
Factsheet
Compsopogon
(Compsopogonaceae)
Filaments more than one cell wide
Factsheet
Sewage fungus
Sphaerotilus
(Comamonadaceae)
Blue-green, grey, whitish or reddish - no organelles
Factsheet
Yellow-green algae
Botrydiopsis
(Botrydiopsidaceae)
Cells containing membrane-bound organelles
Factsheet
Tribonema
(Tribonemataceae)
Cell walls composed of overlapping pieces
Factsheet
Vaucheria
(Vaucheriaceae)
Branch points roughly equal
Factsheet