• Abbotia araneosa Perestenko, 1975 accepted as Neoabbottiella araneosa (Perestenko) S.C.Lindstrom, 1985
• Abbottella concinna Hollenberg, 1967
• Abbottia araneosa L.P.Perestenko, 1997 accepted as Neoabbottiella araneosa (Perestenko) S.C.Lindstrom, 1985
• Abroteia orbicularis J.Agardh, 1876 accepted as Abroteia suborbicularis (Harvey) J.Agardh, 1878
• Abroteia suborbicularis (Harvey) J.Agardh, 1878
• Acanthobolus brasiliensis Kützing, 1843 accepted as Endocladia vernicata J.Agardh, 1841
• Acanthoceras dalmaticum (Meneghini) Frauenfeld, 1855 accepted as Ceramium dalmaticum Meneghini, 1844 accepted as Ceramium echionotum J.Agardh, 1844
• Acanthoceras shuttleworthianum Kützing, 1842 accepted as Ceramium shuttleworthianum (Kützing) Rabenhorst, 1847
• Acanthoceras shuttleworthianum var. breviarticulatum Kützing, 1862 (uncertain)
• Acanthoceras shuttleworthianum var. longiarticulatum Kützing, 1862 (uncertain)
• Acanthoceras transcurrens Kützing, 1849 accepted as Ceramium echionotum J.Agardh, 1844
• Acanthochondria falkenbergii Weber-van Bosse, 1888 accepted as Acanthophora dendroides Harvey, 1855
• Acanthocladia anglica Bennett (uncertain)
• Acanthocladia asperrima Ruprecht (uncertain)
• Acanthocladia hamulosa Ruprecht (uncertain)
• Acanthococcus acicularis (J.Agardh) J.Agardh, 1852 accepted as Mychodea acicularis (J.Agardh) Kraft, 1978
• Acanthococcus aciculiferus Lagerheim, 1883 accepted as Glochiococcus aciculiferus (Lagerheim) P.C.Silva, 1996
• Acanthococcus aciculiferus f. minor Reinsch (uncertain)
• Acanthococcus aciculiferus var. pulcher Hansgirg, 1888 accepted as Trochiscia aciculifera var. pulchra (Hansgirg) Hansgirg, 1888
• Acanthococcus aculiferus Lagerheim, 1883 accepted as Glochiococcus aciculiferus (Lagerheim) P.C.Silva, 1996
• Acanthococcus antarcticus Hooker f. & Harvey, 1845
• Acanthococcus argutus Reinsch, 1886 accepted as Trochiscia arguta (Reinsch) Hansgirg, 1888
• Acanthococcus argutus f. minor Reinsch (uncertain)
• Acanthococcus asper Reinsch accepted as Trochiscia aspera (Reinsch) Hansgirg, 1888
• Acanthococcus ewingii Harvey, 1860 accepted as Mychodea hamata Harvey, 1860
• Acanthococcus gracilaria Sonder, 1853 accepted as Mychodea membranacea Hooker f. & Harvey, 1847
• Acanthococcus granulatus Reinsch, 1886 accepted as Trochiscia granulata (Reinsch) Hansgirg, 1888
• Acanthococcus granulatus var. aerophilus Printz, 1921
• Acanthococcus hirtus (Reinsch) Lagerheim, 1883 accepted as Trochiscia hirta (Reinsch) Hansgirg, 1888
• Acanthococcus hystrix Reinsch, 1886 accepted as Trochiscia hystrix (Reinsch) Hansgirg, 1888
• Acanthococcus insignis Reinsch, 1886 accepted as Trochiscia insignis (Reinsch) Hansgirg, 1888
• Acanthococcus obtusangulus Harvey, 1863 accepted as Mychodea hamata Harvey, 1860
• Acanthococcus obtusus Reinsch, 1886 accepted as Trochiscia obtusa (Reinsch) Hansgirg, 1888
• Acanthococcus pachydermus Reinsch, 1886 accepted as Trochiscia pachyderma (Reinsch) Hansgirg, 1888
• Acanthococcus plicatus Reinsch, 1886 accepted as Trochiscia plicata (Reinsch) Hansgirg, 1888
• Acanthococcus pusillus (Harvey) Harvey, 1863 accepted as Mychodea pusilla (Harvey) J.Agardh, 1872
• Acanthococcus reticularis Reinsch, 1886 accepted as Trochiscia reticularis (Reinsch) Hansgirg, 1888
• Acanthococcus reticularis f. minor Reinsch (uncertain)
• Acanthococcus retusus Reinsch, 1886 accepted as Trochiscia retusa (Reinsch) Hansgirg, 1888
• Acanthococcus spinosus Reinsch, 1886 accepted as Trochiscia spinosa (Reinsch) Hansgirg, 1888
• Acanthococcus spinuliger (J.Agardh) J.Agardh, 1851 accepted as Acanthococcus antarcticus Hooker f. & Harvey, 1845
• Acanthococcus spinuligerus (J.Agardh) J.Agardh (uncertain)
• Acanthococcus spinuligerus var. tenuior (Kützing) Hariot (uncertain)
• Acanthococcus sporoides Reinsch (uncertain)
• Acanthococcus subulatus (C.Agardh) J.Agardh, 1852 accepted as Agardhiella subulata (C.Agardh) Kraft & M.J.Wynne, 1979
• Acanthonema montagnei J.Agardh, 1846 accepted as Camontagnea oxyclada (Montagne) Pujals, 1981
• Acanthopeltis hirsuta (Okamura) S.Shimada, T.Horiguchi & Masuda, 1999 accepted as Gelidium hirsutum (Okamura) G.H.Boo & R.Terada, 2016
• Acanthopeltis japonica Okamura, 1892 accepted as Gelidium yoshidae G.H.Boo & R.Terada, 2016
• Acanthopeltis longiramulosa Y.P.Lee & B.S.Kim, 2003 accepted as Gelidium longiramulosum (Y.P.Lee & B.S.Kim) G.H.Boo, 2016
• Acanthophora antillarum Montagne ex Kützing, 1865 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora aokii Okamura, 1934
• Acanthophora arborea Harvey, 1859 accepted as Chiracanthia arborea (Harvey) Falkenberg, 1897
• Acanthophora delilei Greville, 1830 accepted as Acanthophora nayadiformis (Delile) Papenfuss, 1968
• Acanthophora delilei J.V.Lamouroux, 1813 accepted as Acanthophora nayadiformis (Delile) Papenfuss, 1968
• Acanthophora dendroides Harvey, 1855
• Acanthophora intermedia H.L.Crouan & P.M.Crouan, 1865 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora militaris J.V.Lamouroux accepted as Acanthophora muscoides (Linnaeus) Bory de Saint-Vincent, 1828
• Acanthophora muscoides (Linnaeus) Bory de Saint-Vincent, 1828
• Acanthophora muscoides var. ramosissima Sonder accepted as Acanthophora ramulosa Lindenberg ex Kützing, 1843
• Acanthophora muscoides var. turneri (C.Agardh) Trevisan
• Acanthophora nayadiformis (Delile) Papenfuss, 1968
• Acanthophora orientalis J.Agardh, 1863 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora orientalis f. wightii (J.Agardh) Sonder accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora orientalis var. wightii (J.Agardh) Sonder, 1879 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora pacifica (Setchell) Kraft, 1979
• Acanthophora ramulosa Lindenberg ex Kützing, 1843
• Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora spicifera f. orientalis (J.Agardh) Weber Bosse, 1923 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora spicifera f. wightii (J.Agardh) Weber-van Bosse, 1923 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora spicifera var. orientalis (J.Agardh) Zaneveld, 1956 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora tasmanica Sonder, 1853 accepted as Pityophykos tasmanica (Sonder) Papenfuss, 1958
• Acanthophora thierryi J.V.Lamouroux, 1813 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora thierryi f. gracilis P.L.Crouan & H.M.Crouan, 1878 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthophora triangularis (J.F.Gmelin) Gaillon, 1828 accepted as Alsidium triquetrum (S.G.Gmelin) Trevisan, 1845
• Acanthophora wightii J.Agardh, 1863 accepted as Acanthophora spicifera (M.Vahl) Børgesen, 1910
• Acanthosiphonia echinata (Harvey) Savoie & G.W.Saunders, 2018
• Acanthotylus herediae (Clemente) Kützing, 1843 accepted as Phyllophora herediae (Clemente) J.Agardh, 1842
• Acarposporophycos brasiliensis (Necchi) Necchi & A.S.García, 2019
• Acletoa tarazonae M.S.Calderon & S.M.Boo, 2017
• Acrocarpus capitatus Kützing, 1868 accepted as Gelidiopsis capitata (Kützing) Lipkin & P.C.Silva, 2002
• Acrocarpus clavatus Agardh ex Fraunenfeld, 1854 (uncertain)
• Acrocarpus corymbosus Kützing, 1868 accepted as Gelidium crinale var. corymbosum (Kützing) Feldmann & G.Hamel, 1936
• Acrocarpus crinalis (Turner) Kützing, 1843 accepted as Gelidium crinale (Hare ex Turner) Gaillon, 1828
• Acrocarpus delicatulus Kützing, 1868 accepted as Gelidium crinale (Hare ex Turner) Gaillon, 1828
• Acrocarpus gracilis Kützing, 1849 accepted as Ceratodictyon variabile (J.Agardh) R.E.Norris, 1987
• Acrocarpus intricatus (C.Agardh) Kützing, 1868 accepted as Ceratodictyon intricatum (C.Agardh) R.E.Norris, 1987
• Acrocarpus lubricus Kützing, 1843 accepted as Gelidiella lubrica (Kützing) Feldmann & Hamel, 1934
• Acrocarpus plumula (Esper) C.Agardh (uncertain)
• Acrocarpus pulvinatus (C.Agardh) Kützing, 1849 accepted as Gelidium pulvinatum Thuret ex Bornet, 1876
• Acrocarpus pusillus (Stackhouse) Kützing, 1849 accepted as Gelidium pusillum (Stackhouse) Le Jolis, 1863
• Acrocarpus ramellosus Kützing, 1843 accepted as Huismaniella ramellosa (Kützing) G.H.Boo & S.M.Boo, 2016
• Acrocarpus spathulatus Kützing, 1868 accepted as Gelidium spathulatum (Kützing) Bornet, 1892
• Acrocarpus spinescens Kützing, 1843 accepted as Gelidium crinale (Hare ex Turner) Gaillon, 1828
• Acrochaetium acanthophora Aziz ex Garbary, 1987 (uncertain)
• Acrochaetium actinocladum I.A.Abbott, 1962
• Acrochaetium affine M.A.Howe & Hoyt, 1916
• Acrochaetium agardhiellae A.B.Joly & Cordeiro, 1963
• Acrochaetium alacranense Aziz ex Garbary, 1987 (uncertain)
• Acrochaetium alariae (Jónsson) Bornet, 1904
• Acrochaetium alcyonidiae C.C.Jao