Abacum rudis (A. Combaz) P. Pittau † (basis of record)
Abas wittii (Grunow) R. Ross & P.A. Sims, 1980 (basis of record)
Abbottella concinna Hollenberg, 1967 (basis of record)
Abbottia araneosa L.P. Perestenko, 1997 accepted as  (basis of record)
Abedinium dasypus (Cachon & Cachon-Enjumet) A.R. Loeblich Jr. & A.R. Loeblich III, 1966 (basis of record)
Abratopdinium cardioforme S. Mao & B.A.R. Mohr, 1992 † (basis of record)
Abratopdinium kerguelense S. Mao & B.A.R. Mohr, 1992 † (basis of record)
Abrotanifolia barbata Stackhouse, 1809 accepted as Cystoseira barbata (Stackhouse) C. Agardh, 1820 (basis of record)
Abroteia orbicularis J.G. Agardh, 1876 (basis of record)
Acanthoceras madeburgensis Hongimann, 1910 (basis of record)
Acanthoceras shuttleworthianum Kützing, 1842 accepted as Ceramium shuttleworthianum (Kützing) Rabenhorst, 1847 (basis of record)
Acanthoceras transcurrens Kützing accepted as Ceramium echionotum J.G. Agardh, 1844 (basis of record)
Acanthoceras zachariasii (Brun) Simonsen (basis of record)
Acanthococcus acicularis (J.G. Agardh) J.G. Agardh, 1852 accepted as Mychodea aciculare (J.G. Agardh) Kraft, 1978 (basis of record)
Acanthococcus aciculiferus Lagerheim, 1883 accepted as Trochiscia aciculifera (Lagerheim) Hansgirg, 1888 (basis of record)
Acanthococcus antarcticus J.D. Hooker & Harvey, 1845 (basis of record)
Acanthococcus asper Reinsch accepted as Trochiscia aspera (Reinsch) Hansgirg, 1888 (basis of record)
Acanthococcus ewingii Harvey, 1860 accepted as Mychodea hamata Harvey, 1860 (basis of record)
Acanthococcus gracilaria Sonder, 1853 accepted as Mychodea gracilaria (Sonder) Sonder, 1880 (basis of record)
Acanthococcus granulatus Reinsch, 1886 accepted as Trochiscia granulata (Reinsch) Hansgirg, 1888 (basis of record)
Acanthococcus pusillus (Harvey) Harvey, 1863 accepted as Mychodea pusilla (Harvey) J.G. Agardh, 1872 (basis of record)
Acanthococcus reticularis Reinsch accepted as Trochiscia reticularis (Reinsch) Hansgirg, 1888 (basis of record)
Acanthococcus spinuliger (J.G. Agardh) J.G. Agardh, 1851 accepted as Acanthococcus antarcticus J.D. Hooker & Harvey, 1845 (basis of record)
Acanthocodium fragile Suringar, 1867 accepted as Codium fragile (Suringar) Hariot, 1889 (basis of record)
Acanthodiacrodium arburense P. Pittau † (basis of record)
Acanthodiacrodium mamillatum P. Pittau † (basis of record)
Acanthodinium spinosum Kofoid, 1907 (basis of record)
Acanthogonyaulax spinifera (Murray & Whitting) H.W. Graham, 1942 (basis of record)
Acanthoica acanthifera Lohmann ex Lohmann, 1913 (basis of record)
Acanthoica aculeata Kamptner, 1941 (basis of record)
Acanthoica bidentula Lecal-Schlauder, 1951 (basis of record)
Acanthoica biscayensis A. Kleijne, 1992 (basis of record)
Acanthoica cidaris J. Schlauder (basis of record)
Acanthoica coronata Lohmann, 1903 (basis of record)
Acanthoica lithostratos Schiller, 1926 accepted as Anacanthoica lithostratos (Schiller) Norris, 1984 (basis of record)
Acanthoica maxima Heimdal, 1981 (basis of record)
Acanthoica monospina Schiller, 1914 (basis of record)
Acanthoica quattrospina Lohmann, 1903 (basis of record)
Acanthoica rubens Kamptner, 1941 (basis of record)
Acanthoica schilleri Conrad, 1928 (basis of record)
Acanthopeltis hirsuta (Okamura) S. Shimada, T. Horiguchi & Masuda (basis of record)
Acanthopeltis japonica Okamura, 1892 (basis of record)
Acanthopeltis longiramulosa Y. Lee & B. Kim, 2003 (basis of record)
Acanthophora aokii Okamura, 1934 (basis of record)
Acanthophora arborea Harvey, 1859 accepted as Chiracanthia arborea (Harvey) Falkenberg, 1897 (basis of record)
Acanthophora delilei J.V. Lamouroux, 1813 accepted as Acanthophora nayadiformis (Delile) Papenfuss, 1968 (basis of record)
Acanthophora delilei Greville, 1830 accepted as Acanthophora nayadiformis (Delile) Papenfuss, 1968 (basis of record)
Acanthophora dendroides Harvey, 1855 (basis of record)
Acanthophora intermedia H.L. Crouan & P.M. Crouan in Schramm & Mazé, 1865 accepted as Acanthophora spicifera (M. Vahl) Børgesen, 1910 (basis of record)
Acanthophora muscoides (Linnaeus) Bory de Saint-Vincent, 1828 (basis of record)
Acanthophora nayadiformis (Delile) Papenfuss, 1968 (basis of record)
Acanthophora orientalis J.G. Agardh, 1863 accepted as Acanthophora spicifera (M. Vahl) Børgesen, 1910 (basis of record)
Acanthophora pacifica (Setchell) Kraft, 1979 (basis of record)
Acanthophora ramulosa Lindenberg ex Kützing, 1843 (basis of record)
Acanthophora spicifera (M. Vahl) Børgesen, 1910 (basis of record)
Acanthophora tasmanica Sonder, 1853 accepted as Pityophykos tasmanica (Sonder) Papenfuss, 1958 (basis of record)
Acanthophora thierryi J.V. Lamouroux, 1813 accepted as Acanthophora spicifera (M. Vahl) Børgesen, 1910 (basis of record)
Acanthophora wightii J.G. Agardh, 1863 accepted as Acanthophora spicifera (M. Vahl) Børgesen, 1910 (basis of record)
Acetabularia acetabulum (Linnaeus) P.C. Silva, 1952 (basis of record)
Acetabularia antillana (Solms-Laubach) Egerod, 1952 (basis of record)
Acetabularia clavata Yamada, 1934 accepted as  (basis of record)
Acetabularia crenulata J.V. Lamouroux, 1816 (basis of record)
Acetabularia dentata Solms-Laubach, 1895 (basis of record)
Acetabularia denudata Zanardini, 1878 accepted as Acetabularia major G. Martens, 1866 (basis of record)
Acetabularia exigua Solms-Laubach, 1895 accepted as Parvocaulis polyphysoides (P.L. Crouan & H.M. Crouan) S. Berger, U. Fettweiss, S. Gleissberg, L.B. Liddle, U. Richter, H. Sawitzky, H. & G.C. Zuccarello, 2003 (basis of record)
Acetabularia farlowii Solms-Laubach, 1895 (basis of record)
Acetabularia gigas Solms-Laubach, 1895 accepted as Acetabularia major G. Martens, 1866 (basis of record)
Acetabularia integra J.V. Lamouroux accepted as Acetabularia acetabulum (Linnaeus) P.C. Silva, 1952 (basis of record)
Acetabularia kilneri J.G. Agardh, 1887 (basis of record)
Acetabularia major G. Martens, 1866 (basis of record)
Acetabularia mediterranea J.V. Lamouroux, 1816 accepted as Acetabularia acetabulum (Linnaeus) P.C. Silva, 1952 (basis of record)
Acetabularia minutissima Okamura, 1912 accepted as  (basis of record)
Acetabularia moebii Solms-Laubach, 1895 accepted as  (basis of record)
Acetabularia myriospora A.B. Joly & Cordeiro-Marina, 1965 accepted as Polyphysa myriospora (A.B. Joly & Cordiero-Marinha) S. Berger & M.J. Kaever, 1992 (basis of record)
Acetabularia parvula Solms-Laubach, 1895 accepted as  (basis of record)
Acetabularia peniculus (R. Brown ex Turner) Solms-Laubach, 1895 (basis of record)
Acetabularia polyphysoides P.L. Crouan & H.M. Crouan, 1865 accepted as Parvocaulis polyphysoides (P.L. Crouan & H.M. Crouan) S. Berger, U. Fettweiss, S. Gleissberg, L.B. Liddle, U. Richter, H. Sawitzky, H. & G.C. Zuccarello, 2003 (basis of record)
Acetabularia pusilla (M.A. Howe) F.S. Collins, 1909 accepted as  (basis of record)
Acetabularia ryukyuensis Okamura & Yamada, 1932 (basis of record)
Acetabularia schenckii K. Möbius, 1889 (basis of record)
Acetabularia suhrii Solms-Laubach, 1895 accepted as accepted as Acetabularia caliculus J.V. Lamouroux, 1824 (basis of record)
Acetabularia toxasii Troño, Santiago & Ganzon-Fortes, 1978 (basis of record)
Acetabularia velasquezii Troño, Santiago & Ganzon-Fortes, 1978 accepted as  (basis of record)
Acetabularia wettsteinii Schussnig, 1930 accepted as  (basis of record)
Acetabulum pusilla M. Howe accepted as  (basis of record)
Achnantheiopsis apiculata (R.M. Patrick) H. Lange-Bertalot, 1997 accepted as Planothidium apiculatum (R.M. Patrick) H. Lange-Bertalot, 1999 (basis of record)
Achnantheiopsis aueri (Krasske) H. Lange-Bertalot, 1997 accepted as  (basis of record)
Achnantheiopsis biporoma (M.H. Hohn & Hellerman) H. Lange-Bertalot, 1997 accepted as Planothidium biporomum (M.H. Hohn & Hellerman) H. Lange-Bertalot, 1999 (basis of record)
Achnantheiopsis borneolanceolata H. Lange-Bertalot, 1997 accepted as Planothidium borneolanceolatum (H. Lange-Bertalot) H. Lange-Bertalot (basis of record)
Achnantheiopsis chilensis (Hustedt) H. Lange-Bertalot, 1997 accepted as Planothidium chilense (Hustedt) H. Lange-Bertalot (basis of record)
Achnantheiopsis daui (Foged) H. Lange-Bertalot, 1997 accepted as Planothidium daui (Foged) H. Lange-Bertalot (basis of record)
Achnantheiopsis delicatula (Kützing) H. Lange-Bertalot, 1997 (basis of record)
Achnantheiopsis distincta (Messikommer) H. Lange-Bertalot, 1997 (basis of record)
Achnantheiopsis dubia (Grunow) H. Lange-Bertalot, 1997 accepted as Achnanthes lanceolata (Brébisson ex Kützing) Grunow, 1880 (basis of record)
Achnantheiopsis engelbrechtii (Cholnoky) H. Lange-Bertalot, 1997 accepted as Achnanthes delicatula (Kützing) Grunow, 1880 (basis of record)
Achnantheiopsis fonticolanceolata (H. Lange-Bertalot & Schimanski) H. Lange-Bertalot, 1997 accepted as Planothidium fonticolanceolatum (H. Lange-Bertalot & Schimanski) H. Lange-Bertalot (basis of record)
Achnantheiopsis fragilarioides (J.B. Petersen) H. Lange-Bertalot, 1997 (basis of record)
Achnantheiopsis frequentissima (H. Lange-Bertalot) H. Lange-Bertalot, 1997 (basis of record)
Achnantheiopsis grana (M.H. Hohn & Hellerman) H. Lange-Bertalot, 1997 accepted as Planothidium granum (M.H. Hohn & Hellerman) H. Lange-Bertalot (basis of record)
Achnantheiopsis hauckiana (Grunow) H. Lange-Bertalot, 1997 accepted as Achnanthes delicatula (Kützing) Grunow, 1880 (basis of record)