Acinetospora Bornet, 1891 (basis of record)
Acinetospora crinita (Carmichael) Sauvageau, 1899 (basis of record)
Acrochaete N.Pringsheim, 1862 accepted as Ulvella P.L.Crouan & H.M.Crouan, 1859 (basis of record)
Acrochaete geniculata (N.L.Gardner) O'Kelly, 1983 accepted as Ulvella geniculata (N.L.Gardner) R.Nielsen, C.J.O'Kelly & B. Wysor, 2013 (basis of record)
Acrochaete inflata (Ercegovic) Gallardo, Gómez Garreta, M.A.Ribera, Cormaci, G.Furnari, Giaccone & Boudouresque, 1993 accepted as Ulvella inflata (Ercegovic) R.Nielsen, C.J.O'Kelly & B. Wysor, 2013 (basis of record)
Acrochaete leptochaete (Huber) R.Nielsen, 1983 accepted as Ulvella leptochaete (Huber) R.Nielsen, C.J.O'Kelly & B.Wysor, 2013 (basis of record)
Acrochaete repens Pringsheim, 1862 accepted as Ulvella repens (Pringsheim) R.Nielsen, C.J.O'Kelly & B.Wysor, 2013 (basis of record)
Acrochaete viridis (Reinke) R.Nielsen, 1979 accepted as Ulvella viridis (Reinke) R.Nielsen, C.J.O'Kelly & B.Wysor, 2013 (basis of record)
Acrochaete wittrockii (Wille) R.Nielsen, 1983 accepted as Ulvella wittrockii (Wille) R.Nielsen, C.J.O'Kelly & B.Wysor, 2013 (basis of record)
Acrochaetiaceae Melchior, 1954 (basis of record)
Acrochaetiales (basis of record)
Acrochaetium Nägeli, 1858 (basis of record)
Acrochaetium alariae (Jónsson) Bornet, 1904 (basis of record)
Acrochaetium battersianum Hamel, 1927 (basis of record)
Acrochaetium brebneri (Batters) Hamel, 1928 (basis of record)
Acrochaetium catenulatum M.Howe, 1914 (basis of record)
Acrochaetium codii Hamel, 1927 accepted as Colaconema caespitosum (J.Agardh) Jackelman, Stegenga & J.J.Bolton, 1991 (basis of record)
Acrochaetium corymbiferum (Thuret) Batters, 1902 accepted as Colaconema corymbiferum (Thuret) Alongi, Cormaci & G.Furnari, 2017 (basis of record)
Acrochaetium densum (K.M.Drew) Papenfuss, 1945 accepted as Acrochaetium catenulatum M.Howe, 1914 (basis of record)
Acrochaetium endozoicum (Darbishire) Batters, 1902 (basis of record)
Acrochaetium gynandrum (Rosenvinge) Hamel, 1927 accepted as Colaconema gynandrum (Rosenvinge) R.Nielsen, 1994 (basis of record)
Acrochaetium hallandicum (Kylin) Hamel, 1927 accepted as Colaconema hallandicum (Kylin) Afonso-Carillo, Sanson, Sangil & Diaz-Villa, 2007 (basis of record)
Acrochaetium humile (Rosenvinge) Børgesen, 1915 (basis of record)
Acrochaetium immersum (Rosenvinge) Hamel, 1927 (basis of record)
Acrochaetium infestans M.Howe & Hoyt, 1916 accepted as Colaconema infestans (M.Howe & Hoyt) Woelkerling, 1973 (basis of record)
Acrochaetium leptonema (Rosenvinge) Børgesen, 1915 accepted as Colaconema leptonema (Rosenvinge) Alongi, Cormaci & G.Furnari, 2017 (basis of record)
Acrochaetium lorrain-smithiae (Lyle) L.Newton, 1931 (basis of record)
Acrochaetium microfilum C.-C.Jao, 1936 (basis of record)
Acrochaetium microscopicum (Nägeli ex Kützing) Nägeli, 1858 (basis of record)
Acrochaetium moniliforme (Rosenvinge) Børgesen, 1915 (basis of record)
Acrochaetium parvulum (Kylin) Hoyt, 1920 (basis of record)
Acrochaetium sanctae-mariae (Darbishire) Hamel, 1927 (basis of record)
Acrochaetium savianum (Meneghini) Nägeli, 1862 accepted as Colaconema savianum (Meneghini) R.Nielsen, 1994 (basis of record)
Acrochaetium secundatum (Lyngbye) Nägeli, 1858 (basis of record)
Acrochaetium sparsum (Harvey) Nägeli, 1862 (basis of record)
Acrochaetium stilophorae (Levring) Kylin, 1944 (basis of record)
Acrochaetium subtilissimum (Kützing) Hamel, 1927 accepted as Colaconema subtilissimum (Kützing) Alongi, Cormaci & G.Furnari, 2017 (basis of record)
Acrochaetium unifilum C.-C.Jao, 1936 (basis of record)
Acrochaetium virgatulum (Harvey) Batters, 1902 accepted as Acrochaetium secundatum (Lyngbye) Nägeli, 1858 (basis of record)
Acrosiphonia J.Agardh, 1846 (basis of record)
Acrosiphonia arcta (Dillwyn) Gain, 1912 (basis of record)
Acrosiphonia sonderi (Kützing) Kornmann, 1962 (basis of record)
Acrosiphonia spinescens (Kützing) Kjellman, 1893 (basis of record)
Acrosiphoniaceae S. Jónsson, 1959 (additional source)
Acrosorium Zanardini ex Kützing, 1869 (basis of record)
Acrosorium reptans (P.Crouan & H.Crouan) Kylin, 1924 accepted as Cryptopleura ramosa (Hudson) L.Newton, 1931 (basis of record)
Acrosorium venulosum (Zanardini) Kylin, 1924 (basis of record)
Acrosymphytaceae S.C.Lindstrom, 1987 (basis of record)
Acrothrix Kylin, 1907 (basis of record)
Acrothrix gracilis Kylin, 1907 (basis of record)
Agardhiella F.Schmitz, 1897 (basis of record)
Agardhiella subulata (C.Agardh) Kraft & M.J.Wynne, 1979 (additional source)
Aglaothamnion Feldmann-Mazoyer, 1941 (basis of record)
Aglaothamnion bipinnatum (P.Crouan & H.Crouan) Feldmann & G.Feldmann, 1948 (basis of record)
Aglaothamnion byssoides (Arnott ex Harvey) C.F.Boudouresque & M.M.Perret-Boudouresque, 1987 accepted as Aglaothamnion tenuissimum (Bonnemaison) Feldmann-Mazoyer, 1941 (basis of record)
Aglaothamnion cordatum (Børgesen) Feldmann-Mazoyer, 1941 (basis of record)
Aglaothamnion diaphanum L'Hardy-Halos & Maggs, 1991 (basis of record)
Aglaothamnion feldmanniae Halos, 1965 (basis of record)
Aglaothamnion gallicum (Nägeli) Halos ex Ardré, 1970 accepted as Gaillona gallica (Nägeli) Athanasiadis, 2016 (basis of record)
Aglaothamnion hookeri (Dillwyn) Maggs & Hommersand, 1993 accepted as Gaillona hookeri (Dillwyn) Athanasiadis, 2016 (basis of record)
Aglaothamnion priceanum Maggs, Guiry & Rueness, 1991 (basis of record)
Aglaothamnion pseudobyssoides (P.Crouan & H.Crouan) Halos, 1965 (basis of record)
Aglaothamnion roseum (Roth) Maggs & L'Hardy-Halos, 1993 accepted as Gaillona rosea (Roth) Athanasiadis, 2016 (basis of record)
Aglaothamnion sepositum (Gunnerus) Maggs & Hommersand, 1993 accepted as Gaillona seposita (Gunnerus) Athanasiadis, 2016 (basis of record)
Aglaothamnion tenuissimum (Bonnemaison) Feldmann-Mazoyer, 1941 (basis of record)
Aglaothamnion tripinnatum (C.Agardh) Feldmann-Mazoyer, 1941 (basis of record)
Ahnfeltia Fries, 1836 (basis of record)
Ahnfeltia plicata (Hudson) E.M.Fries, 1836 (basis of record)
Ahnfeltiaceae Maggs & Pueschel, 1989 (basis of record)
Ahnfeltiales (basis of record)
Ahnfeltiopsis P.C.Silva & DeCew, 1992 (basis of record)
Ahnfeltiopsis devoniensis (Greville) P.C.Silva & DeCew, 1992 (basis of record)
Alaria Greville, 1830 (basis of record)
Alaria esculenta (Linnaeus) Greville, 1830 (basis of record)
Alariaceae Setchell & Gardner, 1925 (basis of record)
Amphiroa J.V.Lamouroux, 1812 (basis of record)
Amphiroa cryptarthrodia Zanardini, 1843 (basis of record)
Amphiroa rigida J.V.Lamouroux, 1816 (basis of record)
Anadyomenaceae Kützing, 1843 (basis of record)
Anadyomene J.V.Lamouroux, 1812 (basis of record)
Anadyomene stellata (Wulfen) C.Agardh, 1823 (basis of record)
Anotrichium Nägeli, 1862 (basis of record)
Anotrichium barbatum (C.Agardh) Nägeli, 1862 (basis of record)
Anotrichium furcellatum (J.Agardh) Baldock, 1976 (basis of record)
Antithamnion Nägeli, 1847 (basis of record)
Antithamnion cruciatum (C.Agardh) Nägeli, 1847 (basis of record)
Antithamnion densum (Suhr) M.Howe, 1914 (basis of record)
Antithamnion tenuissimum (Hauck) Schiffner, 1915 (basis of record)
Antithamnion villosum (Kützing) Athanasiadis, 1993 (basis of record)
Antithamnionella Lyle, 1922 (basis of record)
Antithamnionella elegans (Berthold) J.H.Price & D.M.John, 1986 (basis of record)
Antithamnionella floccosa (O.F.Müller) Whittick, 1980 (basis of record)
Antithamnionella spirographidis (Schiffner) E.M.Wollaston, 1968 (basis of record)
Apoglossocolax Maggs & Hommersand, 1993 (basis of record)
Apoglossocolax pusillus Maggs & Hommersand, 1993 (basis of record)
Apoglossum J.Agardh, 1898 (basis of record)
Apoglossum ruscifolium (Turner) J.Agardh, 1898 (basis of record)
Arthrocladia Duby, 1830 (basis of record)
Arthrocladia villosa (Hudson) Duby, 1830 (basis of record)
Arthrocladiaceae Chauvin, 1842 (basis of record)