• Nitzschia Baer, 1826 [Family: Capsalidae]
• Nitzschia Denny, 1842 accepted as Dennyus Neumann, 1906 [Family: Menoponidae]
• Nitzschia Hassall, 1845 [Family: Bacillariaceae]
• Nitzschia abbreviata Hustedt
• Nitzschia abonuensis Foged
• Nitzschia abridia Camburn
• Nitzschia accedens Hustedt
• Nitzschia accommodata Hustedt
• Nitzschia aciculariformis Manguin, 1957 accepted as Synedropsis laevis (Heiden) G.R. Hasle, L.K. Medlin & E.E. Syvertsen, 1994
• Nitzschia acicularioides Archibald, 1966 accepted as Nitzschia draveillensis Coste & Ricard, 1980
• Nitzschia acicularioides Hustedt
• Nitzschia acicularis (Kützing) W. Smith, 1853
• Nitzschia acidoclinata H. Lange-Bertalot, 1976
• Nitzschia actinastroides (Lemmermann) van Goor, 1925
• Nitzschia actydrophila Hasle, 1965 accepted as Pseudo-nitzschia delicatissima (Cleve) Heiden, 1928
• Nitzschia acula (Kützing) Hantzsch accepted as Tryblionella acuta (Cleve) D.G. Mann, 1990
• Nitzschia acula Hantzsch ex Cleve & Grunow
• Nitzschia acuminata (W. Smith) Grunow, 1880 accepted as Tryblionella acuminata W. Smith, 1853
• Nitzschia acuta Cleve, 1878 accepted as Tryblionella acuta (Cleve) D.G. Mann, 1990
• Nitzschia acuta Hantzsch
• Nitzschia acuta Peragallo & Peragallo, 1899 accepted as Tryblionella acuta (Cleve) D.G. Mann, 1990
• Nitzschia adamata Hustedt, 1957
• Nitzschia adamatoides K. Krammer & H. Lange-Bertalot
• Nitzschia adapta Hustedt
• Nitzschia adducta Hustedt, 1955 accepted as Tryblionella adducta (Hustedt) D.G. Mann, 1990
• Nitzschia adductoides Archibald
• Nitzschia admissa Hustedt, 1957
• Nitzschia admissoides Cholnoky
• Nitzschia aequalis Hustedt
• Nitzschia aequora Hustedt, 1939
• Nitzschia aequorea Hustedt, 1939
• Nitzschia aerophila Hustedt, 1942 accepted as Tryblionella aerophila (Hustedt) D.G. Mann, 1990
• Nitzschia aerophiloides H.P. Gandhi
• Nitzschia aestuari Hustedt
• Nitzschia affinis Grunow, 1862
• Nitzschia africana Grunow
• Nitzschia agnewii Cholnoky
• Nitzschia agnita Hustedt, 1957
• Nitzschia alba J.C. Lewin & R.A. Lewin, 1967
• Nitzschia albicostalis B.E. Volcani & C.-W. Li
• Nitzschia alexandrina (Cholnoky) H. Lange-Bertalot & Simonsen
• Nitzschia alicae Hlúbiková & Ector, 2009
• Nitzschia allanssonii Cholnoky
• Nitzschia alpina Hustedt, 1943
• Nitzschia alpinobacillum H. Lange-Bertalot
• Nitzschia amabilis Suzuki, 2010
• Nitzschia ambigua Manguin, 1964
• Nitzschia americana G.R. Hasle, 1964 accepted as Pseudo-nitzschia americana (G.R. Hasle) G.A. Fryxell, 1993
• Nitzschia amisaensis Foged
• Nitzschia amphibia Grunow, 1862
• Nitzschia amphibioides Hustedt, 1942
• Nitzschia amphicephala Grunow
• Nitzschia amphioxoides Hustedt
• Nitzschia amphioxys (Ehrenberg) W. Smith, 1853 accepted as Hantzschia amphioxys (Ehrenberg) Grunow, 1880
• Nitzschia amphiplectans Hustedt, 1957
• Nitzschia amphiprora Grunow
• Nitzschia amplectens Hustedt, 1957
• Nitzschia amundonii Aleem
• Nitzschia anassae Cholnoky
• Nitzschia andicola H. Lange-Bertalot & U. Rumrich
• Nitzschia angularis W. Smith, 1853
• Nitzschia angulata Hasle, 1972 accepted as Fragilariopsis rhombica (O'Meara) Hustedt, 1952
• Nitzschia angustata (W. Smith) Grunow, 1880
• Nitzschia angustatula H. Lange-Bertalot, 1987
• Nitzschia angusteforaminata H. Lange-Bertalot
• Nitzschia angustiforaminata H. Lange-Bertalot, 1980
• Nitzschia aniae H. Lange-Bertalot
• Nitzschia antarctica Okuno, 1954 accepted as Fragilariopsis rhombica (O'Meara) Hustedt, 1952
• Nitzschia apiceconica Kufferath, 1956
• Nitzschia apiculata (Gregory) Grunow, 1878 accepted as Tryblionella apiculata Gregory, 1857 accepted as Nitzschia constricta (Kützing) Ralfs, 1861
• Nitzschia apiculata (W. Gregory) Grunow, 1880 accepted as Nitzschia constricta (Kützing) Ralfs, 1861
• Nitzschia archibaldii H. Lange-Bertalot
• Nitzschia arcuata Gregory ex Greville
• Nitzschia arcula R. Gersonde †
• Nitzschia ardua Cholnoky, 1961 accepted as Tryblionella ardua (Cholnoky) D.G. Mann, 1990
• Nitzschia aremonica Archibald
• Nitzschia arenosa M. Garcia-Baptista, 1992
• Nitzschia areolata Hustedt, 1952 accepted as Psammodictyon areolatum (Hustedt) D.G. Mann, 1990
• Nitzschia armoricana (Kützing) Grunow, 1862
• Nitzschia astridiae Aleem
• Nitzschia atomus Hustedt, 1950 accepted as Simonsenia delognei (Grunow) H. Lange-Bertalot, 1979
• Nitzschia attenuata Michailov
• Nitzschia aurantiaca Schoeman
• Nitzschia aurariae Cholnoky
• Nitzschia aurica R. Gersonde †
• Nitzschia auricula R. Gersonde †
• Nitzschia australis (Peragallo) A. Mann, 1937
• Nitzschia austriaca Hustedt, 1959
• Nitzschia bacata Hustedt
• Nitzschia bacillariaeformis Hustedt, 1922
• Nitzschia bacilliformis Hustedt, 1922
• Nitzschia bacillum Hustedt, 1922
• Nitzschia balatonis Grunow, 1880 accepted as Tryblionella balatonis (Grunow) D.G. Mann, 1990
• Nitzschia balcanica Hustedt
• Nitzschia baltica (Juhlin-Dannfelt) M. Peragallo
• Nitzschia barbieri Peragallo, 1921
• Nitzschia barkleyi Hustedt, 1952 accepted as Pseudo-nitzschia lineola (Cleve) Hasle, 1965
• Nitzschia barronii R. Gersonde †
• Nitzschia barrowiana Patrick & Freese
• Nitzschia bartholomei Grunow