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- angulare
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- commissurale
- connatum
- conspersum
- cosmarioides
- crenulatum
- cyclicum
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- denboeri
- depressum
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- difficile
- dilatatum
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- fontigenum
- formosulum
- granatoides
- granatum
- hexalobum
- holmiense
- hornavanense
- hostensiense
- angulare
- humile
- margaritiferum
- meneghinii
- microsphinctum
- monomazum
- nasutum
- neocrenatum
- nymannianum
- obliquum
- obsoletum
- obtusatum
- ornatum
- ovale
- pachydermum
- paragranatoides
- perforatum
- pericymatium
- pokornyanum
- portianum
- protractum
- pseudoconnatum
- pseudoinsigne
- pseudopyramidatum
- punctulatum
- pseudoprotuberans
- pyramidatum
- quadratum
- quinarium
- ralfsii
- regnellii
- regnesi
- reniforme
- June - Cosmarium rostafinskii
- scenedesmus
- sphyrelatum
- striolatum
- subcostatulum
- subexcavatum
- subgranatum
- subprotumidum
- subpunctulatum
- taxichondriforme
- tetrachondrum
- tetraophthalmum
- turpinii
- ungarianum var. subtriplicatum
- venustum
- Cosmocladium
- Cylindrocystis
- Desmidium
- Docidium
- Euastrum
- Gonatozygon
- H-R
- S-X
- Sphaerozosma
- Spirotaenia
- Spondylosium
- Staurastrum
- alternans
- anatinum
- arachne
- bloklandiae
- brachiatum
- brebissonii
- brevispina
- chaetoceras
- cingulum
- controversum
- crassangulatum
- diacanthum
- dilatatum
- echinatum
- elongatum
- furcatum
- furcigerum
- groenbladii
- habeebense
- heimerlianum
- hirsutum
- hystrix
- inconspicuum
- lapponicum
- levanderii
- manfeldtii
- margaritaceum
- monticulosum
- paradoxum
- pileolatum
- pingue
- polytrichum
- punctulatum
- pyramidatum
- scabrum
- sexcostatum
- spongiosum
- teliferum
- tetracerum
- vestitum
- Staurodesmus
- Teilingia
- Tetmemorus
- Tortitaenia
- Xanthidium
- Year
- 2025
- December - Staurastrum paradoxum
- November - Cosmarium tetraophthalmum
- October - Closterium ralfsii
- September - Cosmarium hornavanense
- August - Closterium dianae
- July - Staurastrum anatinum
- June - Cosmarium rostafinskii
- May - Staurastrum groenbladii
- April - Cosmarium beckii
- March - Cosmarium subcostatulum
- February - Closterium rostratum
- January - Cosmarium pseudoprotuberans
- 2024
- December - Cosmarium neocrenatum
- November - Closterium submoniliferum
- October - Cosmarium hostensiense
- September - Closterium kuetzingii
- August - Cosmarium scenedesmus
- July - Cosmarium quadratum
- June - Euastrum minimum
- May - Staurastrum manfeldtii
- April - Closterium incurvum
- March - Cosmarium fontigenum
- February - Cosmarium dickii
- January - Euastrum didelta
- 2023
- December - Closterium praelongum
- November - Cosmarium microsphinctum
- October - Cosmarium pokornyanum
- September - Staurastrum inconspicuum
- August - Cosmarium crenulatum
- July - Euastrum subalpinum
- June - Staurastrum levanderi
- May - Cosmarium microsphinctum
- April - Closterium subscoticum
- March - Cosmarium impressulum
- February - Cosmarium angulare
- January - Staurastrum heimerlianum
- 2022
- December - Closterium juncidum
- November - Cosmarium nasutum
- October - Cosmarium cosmarioides
- September - Staurodesmus patens
- August - Closterium turgidum
- July - Cosmarium subexcavatum
- June - Cosmarium conspersum
- May - Cosmarium excavatum
- April - Closterium directum
- March - Cosmarium anceps
- February - Cosmarium biretum
- January - Closterium baillyanum
- 2021
- December - Staurastrum cingulum
- November - Cosmarium paragranatoides
- October - Closterium attenuatum
- September - Cosmarium granatoides
- August - Cosmarium meneghinii
- July - Cosmarium commissurale
- June - Cosmarium pseudopyramidatum
- May - Staurastrum pingue
- April - Pleurotaenium simplicissimum
- March - Cosmarium ornatum
- February - Gonatozygon aculeatum
- January - Staurastrum monticulosum
- 2020
- December - Cosmarium granatum
- November - Staurastrum tetracerum
- October - Actinotaenium cucurbitinum
- September - Staurodesmus triangularis
- August - Cosmarium regnellii
- July - Staurastrum hirsutum
- June - Euastrum ansatum
- May - Cosmarium monomazum
- April - Cosmarium regnesi
- March - Actinotaenium pinicola
- February -Staurastrum crassangulatum
- January - Euastrum biscrobiculatum
- 2019
- December - Cosmarium hexalobum
- November - Euastrum pulchellum
- October - Cosmarium sphyrelatum
- September - Cosmarium margaritiferum
- August - Xanthidium tenuissimum
- July - Euastrum denticulatum
- June - Cosmarium caelatum
- May - Cosmarium difficile
- April - Spirotaenia diplohelica
- March - Staurastrum arachne
- February - Euastrum gayanum
- January - Cosmarium nasutum
- 2018
- December - Actinotaenium kriegeri
- November - Staurastrum dilatatum
- October - Euastrum pinnatum
- September - Cosmarium pseudoconnatum
- August - Cosmarium connatum
- July - Staurastrum margaritaceum
- June -Closterium nematodes
- May - Cosmarium pachydermum
- April - Euastrum dubium
- March -Staurastrum lapponicum
- February - Cosmarium humile
- January - Actinotaenium riethii
- 2017
- December - Closterium lineatum
- November - Euastrum luetkemuelleri
- Octtober - Cosmarium pyramidatum
- September - Staurastrum punctulatum
- August - Closterium limneticum
- July - Tortitaenia bahusiensis
- June - Pleurotaenium archeri
- May - Cosmarium cyclicum
- April - Euastrum coeselii
- March - Staurastrum pileolatum
- February - Cosmarium obtusatum
- January - Closterium gracile
- 2016
- December - Staurodesmus glaber
- November - Cosmarium taxichondriforme
- October - Heimansia pusilla
- September - Pleurotaenium nodulosum
- August - Euastrum lacustre
- July - Cosmarium tetrachondrum
- June - Euastrum insulare
- May - Staurastrum brebissonii
- April - Closterium cornu
- March - Actinotaenium mooreanum
- February - Cosmarium denboeri
- January - Cosmarium cataractarum
- 2015
- December - Staurastrum pyramidatum
- November - Staurodesmus dickiei
- October - Closterium moniliferum
- September - Staurastrum controversum
- August - Euastrum ventricosum
- July - Actinotaenium inconspiquum
- June - Cosmarium formosulum
- May - Xanthidium bifidum
- April - Staurastrum brevispina
- March - Cosmarium amoenum
- February - Closterium acutum
- January - Tortitaenia trabeculata
- 2014
- December - Staurastrum echinatum
- November - Micrasterias furcata
- October - Staurastrum furcatum
- September - Cosmarium protractum
- August - Staurodesmus pterosporus
- July -Staurodesmus omearae
- June - Closterium calosporum
- May - Pleurotaenium truncatum
- April - Cosmarium portianum
- March - Sphaerozosma aubertianum
- February - Staurastrum scabrum
- January - Micrasterias radiosa
- 2013
- December - Staurodesmus dejectus
- November - Staurastrum alternans
- October - Closterium closterioides
- September - Cosmarium botrytis
- August - Euastrum pseudotuddalense
- July - Staurastrum teliferum
- June - Gonatozygon kinahanii
- May - Xanthidium variabile
- April - Actinotaenium turgidum
- March - Haplotaenium rectum
- February - Staurastrum vestitum
- January - Cosmarium obsoletum
- 2012
- December - Euastrum crassum
- November - Closterium cynthia
- October - Hyalotheca mucosa
- September - Heimansia species
- August - Actinotaenium curtum
- July - Cosmarium turpinii
- June - Staurastrum elongatum
- May - Pleurotaenium ehrenbergii
- April - Euastrum ampullaceum
- March - Closterium acerosum
- February - Roya closterioides
- January - Cosmarium quinarium
- 2011
- December - Staurastrum sexcostatum
- November - Desmidium aptogonum
- October - Actinotaenium phymatosporum
- September - Cosmarium nymannianum
- August - Xanthiddiuum basidentatum
- July - Closterium angustatum
- June - Staurastrum polytrichum
- May - Cosmarium brebissonii
- April - Actinotaenium rufescens
- March - Closterium striolatum
- February - Staurastrum bloklandiae
- January - Cosmarium subprotumidum
- 2010
- December - Pleurotaenium coronatum
- November - Actinotaenium subtile
- October - Spharozosma filiforme
- September - Docidium undulatum
- Augustus - Xanthidium fasciculatum
- July - Closterium navicula
- June - Staurastrum hystrix
- May - Cosmarium ungerianum var. subtriplicatum
- April - Euastrum insigne
- March - Cosmarium venustum
- February - Actinotaenium silvae-nigrae
- January - Penium polymorphum
- 2009
- December - Desmidium baileyi
- November - Closterium pusillum
- October - Cosmarium perforatum
- September - Gonatozygon brebissonii
- August - Cosmarium ovale
- July - Penium exiguum
- June - Cosmocladium perissum
- May - Euastrum binale
- April - Netrium oblongum
- March - Cosmarium subpunctulatum
- February - Tetmemorus laevis
- January - Staurodesmus cuspidatus
- 2008
- December - Penium spirostriolatum
- November - Cosmarium reniforme
- October - Docidium baculum
- September - Actinotaenium cucurbita
- August - Xanthidium octocorne
- July - Tetmemorus granulatus
- June - Cosmarium obliquum
- May - Staurastrum spongiosum
- April - Cosmarium subgranatum
- March - Xanthidium cristatum
- February - Cosmocladium constrictum
- January - Micrasterias oscitans
- 2007
- December - Cylindrocystis gracilis
- November - Micrasterias denticulata
- October - Closterium delpontei
- September - Netrium interruptum
- August - Teilingia granulata
- July - Euastrum bidentatum
- June - Staurastrum diacanthum
- May - Sphaerozosma vertebratum
- April - Spondylosium pulchellum
- March - Staurodesmus extensus
- February - Spirotaenia erythrocephala
- January - Euastrum elegans
- 2006
- December - Closterium setaceum
- November - Actinotaenium diplosporum
- October - Closterium lunula
- September - Euastrum pectinatum
- August - Haplotaenium minutum
- July - Gonatozygon monotaenium
- June - Cylindrocystis brebissonii
- May - Micrasterias jenneri
- April - Roya obtusa
- March - Euastrum humerosum
- February - Mesotaenium macrococcum
- January - Xanthidium armatum
- 2005
- December - Desmidium grevillei
- November - Cosmarium pericymatium
- October - Xanthidium antilopaeum
- September - Bambusina brebissonii
- August - Mesotaenium caldariorum
- July - Micrasterias papillifera
- June - Micrasterias rotata
- May - Pleurotaenium trabecula
- April - Cosmarium ralfsii
- March - Closterium costatum
- February - Micrasterias brachyptera
- January - Tetmemorus brebissonii
- 2004
- December - Euastrum oblongum
- November - Staurodesmus mucronatus
- October - Staurastrum furcigerum
- September - Cosmarium striolatum
- August - Tortitaenia obscura
- July - Spirotaenia condensata
- June - Cosmocladium saxonicum
- May - Micrasterias truncata
- April - Cosmarium holmiense
- March - Penium margaritaceum
- February - Micrasterias apiculata
- January - Staurastrum habeebense
- 2003
- December - Netrium digitus
- November - Micrasterias pinnatifida
- October - Closterium aciculare
- September - Spondylosium ellipticum
- August - Desmidium swartzii
- July - Micrasterias fimbriata
- June - Actinotaenium didymocarpum
- May - Hyalotheca dissiliens
- April - Cosmarium pseudoinsigne
- March - Euastrum verrucosum
- February - Staurodesmus convergens
- January - Staurastrum brachiatum
- 2002
- Additions
- 2017
- Actinotaenium mooreanum (March)
- 2016
- Rotifer eating Micrasterias rotata (September)
- Netrium digitus
- Bambusina brebissonii (June)
- Actinotaenium subtile (January)
- 2015
- Spondylosium pulchellum
- Micrasterias rotata
- Pleurotaenium trabecula - (September)
- Micrasterias crux-melitensis
- Micrasterias brachyptera
- Micrasterias apiculata (August)
- Micrasterias denticulata
- Micrasterias pinnatifida (July)
- Actinotaenium diplosporum (May)
- Cosmarium botrytis
- Sphaerozosma aubertianum - (March)
- Closterium costatum (March)
- 2014
- Sphaerozosma filiforme (November)
- Penium spirostriolatum (September)
- Actinotaenium diplosporum (August)
- Penium margaritaceum (July)
- Euastrum pectinatum (June)
- Desmidium aptogonum (May)
- Staurastrum spongiosum (April)
- Micrasterias papillifera (April)
- Euastrum insigne (April)
- Desmidium baileyi (March)
- Cosmarium ovale (February)
- Staurastrum furcigerum (February)
- Euastrum germanicum (January)
- Euastrum bidentatum (December)
- Cosmarium striolatum (November)
- Cosmarium perforatum (October)
- Biology
- Contact
image © Marien van Westen
Cosmarium hornavanense var. hornavanense. Notice relatively large cell dimensions and semicells with truncate-pyramidal, coarsely granulate outline.
Cell dimensions (L x B): 85 x 65 µm
Image © Marien van Westen
SEM picture of C. hornavanense var. dubovianum, showing cell wall ornamentation in detail.
Cell dimensions (L x B): 76 x 56 µm.
Image © Alfred van Geest
C. hornavanense var. janoviense, characterized by a slightly produced apex of the semicells.
Cell dimensions (L x B): 76 x 56 µm.
Image © Marien van Westen
Empty cell of C. hornavanense var. janoviense showing a transversal band of supraisthmial granules as well.
Desmid of the Month
September 2025Cosmarium hornavanense
Cosmarium hornavanense should be compared with Cosmarium obtusatum (desmid of February 2017), a species with a similar cell outline and cell wall sculpturing. However, cells of C. hornavanense are larger and ornamentation is more pronounced. Usually, a number of short, longitudinal series of granules just above the isthmus may be observed, a feature wanting in C. obtusatum. Within the species C. hornavanense a number of varieties and formae have been described, some of them possibly representing separate species. From the Netherlands, particularly var. dubovianum* is known, to be encountered in various slightly acidic, mesotrophic habitats.
* Originally described as a separate species: C. dubovianum Lütkemüller
Image © Marien van Westen
Empty cell of C. hornavanense var. hornavanense showing both intramarginal and supraisthmial series of granules.
Image © Marien van Westen
C. hornavanense var. dubovianum. Notice slightly lower dimensions (as compared to the nominate variety) and more undulate (rather than granulate) semicell outline.
Cell dimensions: (L x B): 75 x 58 µm.
Image © Marien van Westen
Empty cell of C. hornavanense var. dubovianum. Notice transversal band of supraisthmial granules.
