• Cosmarium Corda ex Ralfs, 1848 [Family: Desmidiaceae]
• Cosmarium Dulac, 1867 (unaccepted) [Family: Ranunculaceae]
• Cosmarium abbreviatum Raciborski, 1885
• Cosmarium abruptum P. Lundell, 1871
• Cosmarium abscissum Lutkem
• Cosmarium achondroides G.S. West
• Cosmarium actinophorum Brühl & Biswas, 1926
• Cosmarium aculeatum Corda
• Cosmarium acutangulum Insam & Krieger, 1936
• Cosmarium acutigonum D.B. Williamson, 1999
• Cosmarium adelochondrum
• Cosmarium adoxum W. West & G.S. West, 1897
• Cosmarium adpressum Noda & Skvortzov
• Cosmarium advolatum Noda & Skvortzov
• Cosmarium aequale W.B. Turner
• Cosmarium aequatum W. West & G.S. West
• Cosmarium aequinoctiale W. West & G.S. West
• Cosmarium aethiopicum W. West & G.S. West
• Cosmarium affine Raciborski
• Cosmarium africanum W. West & G.S. West
• Cosmarium aitchisonii J. Schaarschmidt
• Cosmarium alaskanum Croasdale
• Cosmarium alatum Corda
• Cosmarium allorgei P. Bourrelly
• Cosmarium allum Noda & Skvortzov
• Cosmarium alpestre J. Roy & Bisset, 1893
• Cosmarium alpicolum Schmidle, 1895
• Cosmarium alpigenum Messikommer, 1942
• Cosmarium alpinum Raciborski
• Cosmarium ambadiense Grönblad & Scott
• Cosmarium americanum Lagerheim
• Cosmarium amesii Cushman
• Cosmarium amoenum Brébisson ex Ralfs, 1848
• Cosmarium amoeviforme Hirano
• Cosmarium amphichondrum Skuja
• Cosmarium amplum Nordstedt, 1887
• Cosmarium amurense Skvortzov
• Cosmarium ananense Hinode
• Cosmarium anax W. West & G.S. West
• Cosmarium anceps P. Lundell, 1871
• Cosmarium andinum A. Couté & A. Iltis
• Cosmarium angolense W. West & G.S. West
• Cosmarium angulare L.N. Johnson, 1894
• Cosmarium angulatum (Perty) Rabenhorst, 1868
• Cosmarium angulosum Brébisson, 1856
• Cosmarium angustatum (Wittrock) Nordstedt, 1872
• Cosmarium anisochondrum Nordstedt, 1878
• Cosmarium annulatum (Nägeli) de Bary, 1849
• Cosmarium anomalum Delponte, 1877 accepted as Cosmarium conspersum Ralfs, 1848
• Cosmarium ansatum (Ehrenberg) Corda, 1839 accepted as Euastrum ansatum Ralfs
• Cosmarium ansatum (Ehrenberg) Rabenhorst, 1868 accepted as Cosmarium pseudopyramidatum P. Lundell, 1871
• Cosmarium antarcticum Gain
• Cosmarium anthophorum Couté & Rousselin
• Cosmarium antilopaeum Brébisson, 1840 accepted as Xanthidium antilopaeum (Brébisson) Kützing, 1849
• Cosmarium antioquiense G.S. West
• Cosmarium antiquorum Noda & Skvortzov
• Cosmarium apertiuscula Skuja
• Cosmarium apertiusculum Skuja
• Cosmarium apertum W.B. Turner
• Cosmarium aphanichondrum Nordstedt
• Cosmarium apiatum Scott & Prescott
• Cosmarium arcanum Hinode
• Cosmarium arctoum Nordstedt, 1875
• Cosmarium arcuatum Krieger & Gerloff
• Cosmarium areguense Borge
• Cosmarium ariston Skuja
• Cosmarium armatum Brébisson
• Cosmarium armillatum W.B. Turner
• Cosmarium arnellii Boldt, 1885
• Cosmarium arrense Kouwets, 1997
• Cosmarium arrosum Nordstedt
• Cosmarium arthrodesmiforme Borge
• Cosmarium askenasyi Schmidle, 1895
• Cosmarium asperum M. Dingley, 2004
• Cosmarium asperum W. West & G.S. West
• Cosmarium asphaerosporum Wittrock, 1879
• Cosmarium asterophorum Skuja
• Cosmarium asterosporum P.F.M. Coesel, 1989
• Cosmarium asymmetricum Rich, 1935
• Cosmarium atlanthoideum Delponte
• Cosmarium attenuatum Brébisson ex Ralfs, 1848
• Cosmarium auriculatum Reinsch
• Cosmarium australe
• Cosmarium avalonense Woodhead & Tweed
• Cosmarium aversiforme Krieger & Gerloff
• Cosmarium aversum W. West & G.S. West
• Cosmarium baccatum Scott & Gronblad
• Cosmarium bacciferum W.B. Turner
• Cosmarium bacillare Lütkemuller, 1910 accepted as Actinotaenium inconspicuum (W. West & G.S. West) Teiling, 1954
• Cosmarium baileyi Wolle, 1884
• Cosmarium baillyanum Brébisson ex Meneghini
• Cosmarium balteum W. West & G.S. West
• Cosmarium bantamianum Bernard
• Cosmarium barbaricum Claassen
• Cosmarium baronii W. West & G.S. West
• Cosmarium barrackporeanum W.B. Turner
• Cosmarium basilicum G.S. West, 1899
• Cosmarium basiornatum (Grönblad) Coesel
• Cosmarium basituberculatum Borge
• Cosmarium basituberculoides P. Bourrelly & A. Coute