Abacum M.A. Fombella, 1978 † accepted as Virgatasporites A. Combaz, 1968 † (basis of record)
Abbottella Hollenberg, 1967 (basis of record)
Abbottella Hollenberg, 1967 (extant flag source)
Abratopdinium S. Mao & B.A.R. Mohr, 1992 † (basis of record)
Abrotanifolia Stackhouse, 1809 accepted as Cystoseira C.A. Agardh, 1820 (extant flag source)
Abrotanifolia Stackhouse, 1809 accepted as Cystoseira C.A. Agardh, 1820 (basis of record)
Acanthocerataceae Round, Crawford & Mann, 1990 accepted as Chaetocerotaceae Ralfs, 1861 (basis of record)
Acanthocerataceae Round, Crawford & Mann, 1990 accepted as Chaetocerotaceae Ralfs, 1861 (extant flag source)
Acanthococcus J.D. Hooker & W.H. Harvey, 1845 (extant flag source)
Acanthococcus J.D. Hooker & W.H. Harvey, 1845 (basis of record)
Acanthocodium W.F.R. Suringar, 1867 (basis of record)
Acanthocodium W.F.R. Suringar, 1867 (extant flag source)
Acanthocodium W.F.R. Suringar, 1867 (source of synonymy)
Acanthodinium Kofoid, 1907 (extant flag source)
Acanthodinium Kofoid, 1907 (basis of record)
Acanthoecaceae accepted as Acanthoecidae Norris, 1965 (extant flag source)
Acanthoecaceae accepted as Acanthoecidae Norris, 1965 (basis of record)
Acetabulum Boehmer in Ludwig, 1760 accepted as Acetabularia J.V.F. Lamouroux, 1812 (basis of record)
Acetabulum Boehmer in Ludwig, 1760 accepted as Acetabularia J.V.F. Lamouroux, 1812 (extant flag source)
Achnantheiopsis Lange-Bertalot, 1997 (basis of record)
Achnantheiopsis Lange-Bertalot, 1997 (extant flag source)
Achnanthidiaceae D.G. Mann (basis of record)
Achnanthidiaceae D.G. Mann (extant flag source)
Achomosphaera Evitt, 1963 † (basis of record)
Achradina Lohmann, 1903 accepted as Monaster Schütt, 1895 (basis of record)
Achradina Lohmann, 1903 accepted as Monaster Schütt, 1895 (extant flag source)
Acinetosporaceae Hamel ex J. Feldmann, 1937 (extant flag source)
Acinetosporaceae Hamel ex J. Feldmann, 1937 (basis of record)
Aclistochara R.E. Peck, 1937 † (basis of record)
Aclistocharaceae † accepted as Characeae Agardh, 1824 (basis of record)
Acrocarpus Kützing, 1843 accepted as Gelidiella Feldmann & G. Hamel, 1934 (basis of record)
Acrocarpus Kützing, 1843 accepted as Gelidiella Feldmann & G. Hamel, 1934 (extant flag source)
Acrosymphytaceae S.C. Lindstrom, 1987 (basis of record)
Acrosymphytaceae S.C. Lindstrom, 1987 (extant flag source)
Acrosymphytonema C.F. Boudouresque, M. Perret-Boudouresque & M. Knoepffler-Peguy, 1984 (extant flag source)
Acrosymphytonema C.F. Boudouresque, M. Perret-Boudouresque & M. Knoepffler-Peguy, 1984 (basis of record)
Actinochloridaceae Korshikov, 1953 (basis of record)
Actinochloridaceae Korshikov, 1953 (extant flag source)
Actinodictyon Pantocsek, 1889 † (basis of record)
Actinodiscus Greville, 1863 † (basis of record)
Actinophaenia Shadbolt, 1854 accepted as Actinoptychus Ehrenberg, 1843 (extant flag source)
Actinophaenia Shadbolt, 1854 accepted as Actinoptychus Ehrenberg, 1843 (basis of record)
Actinostephanos G.K. Khursevich, 1989 (basis of record)
Acutochara L. Ya. Sajdakovskij, 1993 † (basis of record)
Adamsiella L.E. Phillips & W.A. Nelson in L.E. Phillips, 2002 (extant flag source)
Adamsiella L.E. Phillips & W.A. Nelson in L.E. Phillips, 2002 (basis of record)
Adenocystaceae F. Rousseau, B. de Reviers, M.-C. Leclerc, A. Asensi & R. Delépine (basis of record)
Adenocystaceae F. Rousseau, B. de Reviers, M.-C. Leclerc, A. Asensi & R. Delépine (extant flag source)
Adlafia G. Moser, H. Lange-Bertalot & D. Metzeltin, 1998 (extant flag source)
Adlafia G. Moser, H. Lange-Bertalot & D. Metzeltin, 1998 (basis of record)
Adnatosphaeridiaceae † (basis of record)
Adnatosphaeridium G. Williams & Downie, 1966 † (basis of record)
Adoneis G.W. Andrews & P. Rivera, 1987 (basis of record)
Adoneis G.W. Andrews & P. Rivera, 1987 (extant flag source)
Aegira Fries, 1825 accepted as Eudesme J.G. Agardh, 1882 (basis of record)
Aegira Fries, 1825 accepted as Eudesme J.G. Agardh, 1882 (extant flag source)
Aeronema J.W. Snow, 1911 accepted as Heterococcus Chodat, 1908 (basis of record)
Aeronema J.W. Snow, 1911 accepted as Heterococcus Chodat, 1908 (extant flag source)
Aerosphaera Gerneck, 1907 (extant flag source)
Aerosphaera Gerneck, 1907 (status source)
Aerosphaera Gerneck, 1907 (basis of record)
Agardhia A. Cabrera, 1823 accepted as Codium Stackhouse, 1797 (extant flag source)
Agardhia A. Cabrera, 1823 accepted as Codium Stackhouse, 1797 (basis of record)
Ahnfeldtia Trevisan, 1849 accepted as Caulerpa J.V.F. Lamouroux, 1809 (extant flag source)
Ahnfeldtia Trevisan, 1849 accepted as Caulerpa J.V.F. Lamouroux, 1809 (basis of record)
Ahnfeltiaceae C.A. Maggs & C.M. Pueschel (basis of record)
Ahnfeltiaceae C.A. Maggs & C.M. Pueschel (extant flag source)
Akkesiphycaceae H. Kawai & H. Sasaki (extant flag source)
Akkesiphycaceae H. Kawai & H. Sasaki (basis of record)
Aldavemyxa Skvortzov, 1972 (basis of record)
Aldavemyxa Skvortzov, 1972 (extant flag source)
Aldorfia L.E. Stover & W.R. Evitt, 1978 (basis of record)
Algites A.C. Seward, 1894 † (basis of record)
Alisphaera Heimdal, 1973 (extant flag source)
Alisphaera Heimdal, 1973 (basis of record)
Alleynea Womersley, 2003 (basis of record)
Alleynea Womersley, 2003 (extant flag source)
Allogonium Kützing, 1843 (basis of record)
Allogonium Kützing, 1843 (extant flag source)
Alloioneis K.M. Schumann ex P.T. Cleve, 1878 accepted as Scoliopleura Grunow, 1860 (extant flag source)
Alloioneis K.M. Schumann ex P.T. Cleve, 1878 accepted as Scoliopleura Grunow, 1860 (basis of record)
Alveolophora A.I. Moisseeva & T.L. Nevretdinova, 1990 † (basis of record)
Alveovallum Lange-Bertalot & Krammer, 2000 (basis of record)
Alveovallum Lange-Bertalot & Krammer, 2000 (extant flag source)
Alveus I. Kaczmarska & G.A. Fryxell, 1996 (extant flag source)
Alveus I. Kaczmarska & G.A. Fryxell, 1996 (basis of record)
Amblyochara L. Grambast, 1963 † (basis of record)
Amblypyrgus R. Gersonde & D.M. Harwood, 1990 † (basis of record)
Amicula Witkowski, Lange-Bertalot & Metzeltin, 2000 (basis of record)
Amiculosphaera R. Harland in L. Montadert et al., 1979 † (basis of record)
Amithalithina J.J. Pospichal & S.W. Wise Jr., 1990 † accepted as Pyrocyclus W.W. Hay & K.M. Towe, 1962 † (basis of record)
Ammodochiaceae † accepted as Ammodochiidae Deflandre, 1950 † (basis of record)
Ammodochium Hovasse, 1932 † (basis of record)
Amoebosporus W.R. Ivimey Cook, 1933 (basis of record)
Amphibia Stackhouse, 1809 accepted as Bostrychia Montagne in Sagra, 1842 (basis of record)
Amphibia Stackhouse, 1809 accepted as Bostrychia Montagne in Sagra, 1842 (extant flag source)
Amphiceratium Vanhöffen, 1896 accepted as Tripos Bory de Saint-Vincent, 1823 (extant flag source)
Amphiceratium Vanhöffen, 1896 accepted as Tripos Bory de Saint-Vincent, 1823 (basis of record)
Amphicocconeis M. De Stefano & D. Marino, 2003 (extant flag source)
Amphicocconeis M. De Stefano & D. Marino, 2003 (basis of record)

 Taxonomic remark

 for Palaeomicrocystis P.K. Maithy, 1975 †

Currently treated as an accepted genus (e.g. in AlgaeBase, 2024 and elsewhere) with type species P. schopfii P. K. ... [details]