Belongs within: Fucales.
Sargassum is a cosmopolitan genus of often large brown algae with a highly differentiated thallus that often dominates the environments in which it is found.
Characters (Norris 2010): Light to dark brown, morphologically differentiated into holdfasts, stipes, terete to compressed axes and branches, leaflike blades, buoyant vesicles, and reproductive branchlets (receptacles). Primary axes with few to numerous, radially or distichously arranged lateral branches of determinate or indeterminate growth, usually above a stipe that is attached below to substratum by a holdfast that is discoid, crustose, conical, or lobed or with protuberances or rhizoidal to rhizomatous. Ultimate branchlets leaflike blades that may be simple or divided, subcylindrical, filiform, or compressed to flattened and broad, with entire, dentate, or serrate margins and with or without a midrib or cryptostomata (sterile pits). Vesicles (usually present) subspherical to ovoid above a pedicel and with or without terminal extensions. Growth from three-sided cell in apical depression. Internally, stipe and branch axes composed of central medulla of elongate cells, surrounded by core of isodiametric cells outward to meristoderm (surface tissue acting as meristem with cells often dividing). Reproductive receptacles (specialised branchlets) developing in axils of lateral branches, ultimate branchlets, and leaflike blades; single or grouped in clusters. Receptacles simple or branched, can be terete, angular, or compressed, with smooth, verrucose, or spinous surface. Conceptacles within receptacles ostiolate, containing either oogonia or antheridia or both.
<==Sargassum Agardh 1820 (nom. cons.) [incl. Hizikia Okamura 1932]SRR14
`--S. subg. SargassumN10
|--S. sect. Herporhizum Dawson ex Norris 2010N10
| |--S. (sect. *Herporhizum) herporhizum Setchell & Gardner 1924N10
| |--S. brandegeei Setchell & Gardner 1924N10
| `--S. liebmannii Agardh 1847N10
|--S. sect. Johnstonii Dawson ex Norris 2010N10
| `--S. (sect. *Johnstonii) johnstonii Setchell & Gardner 1924 [incl. S. guardiense Setchell & Gardner 1924]N10
| |--S. j. f. johnstoniiN10
| `--S. j. f. gracile Setchell & Gardner 1924 [incl. S. j. f. laxius Setchell & Gardner 1924]N10
|--S. sect. Lapazeanum Dawson ex Norris 2010N10
| |--S. (sect. *Lapazeanum) lapazeanum Setchell & Gardner 1924 (see below for synonymy)N10
| |--S. acinacifolium Setchell & Gardner 1924N10
| |--S. macdougalii Dawson 1944N10
| `--S. sonorense Dawson 1960 [=S. asymmetricum Dawson 1944 non Yamada 1942]N10
`--S. sect. Sinicola Dawson ex Norris 2010N10
|--S. (sect. *Sinicola) sinicola Setchell & Gardner 1924 (see below for synonymy)N10
| |--S. s. ssp. sinicolaN10
| `--S. s. ssp. camouii (Dawson) Norris & Yensen in Norris 2010 (see below for synonymy)N10
`--S. horridum Setchell & Gardner 1924N10
Sargassum incertae sedis:
S. acinaria [=Fucus acinaria; incl. S. linifolium]BS-V28
S. agardhianum Farlow ex Agardh 1889N10
S. alternato-pinnatum Yamada 1942 [incl. S. asymmetricum Yamada 1942]N10
S. aquifolium [=Fucus aquifolius]BS-V28
S. bacculariaPA03
S. californicum (Grunow) Setchell 1937 [=S. fuliginosum var. californica Grunow 1916]N10
S. carpophyllum Agardh 1848L27
S. compactum Bory de Saint-Vincent 1828BS-V28
S. confusumKY97
S. cylindrocarpum Setchell & Gardner 1924N10
S. cymosumM88
S. decipiensG05
S. droserifolium Bory de Saint-Vincent 1828BS-V28
S. duplicatum Bory de Saint-Vincent 1828BS-V28
S. esperi Bory de Saint-Vincent 1828BS-V28
S. fallaxG05
S. filipendulaDH90
S. fissifolium (Mertens) Agardh 1824L27
S. flavicans (Mertens) Agardh 1820HS14
S. fulvellumB79
‘Hizikia’ fusiformisKS00
S. granuliferumBS-V28
S. hemiphyllumTS25
S. heteromorphumG05
S. horneriKS00
S. hornschuchiPP64
S. howelli Setchell 1937N10
S. ilicifolium (Turner) Agardh 1820HS14 [=Fucus ilicifoliusBS-V28]
S. lacerifolium (Turner) Agardh 1821L27
S. lendigerum [=Fucus lendigerus]BS-V28
S. ligulatum Agardh 1824HS14
S. linearifoliumG05
S. macroparpumC-SC06
S. muticum (Yendo) Fensholt 1955 [=S. kjellmanianum f. muticum Yendo 1907]AH76
S. natans (Linnaeus) Borg. 1914L27 [=Fucus natansBS-V28]
S. oligocystum Montagne 1845HS14
S. pacificum Bory de Saint-Vincent 1828N10
S. palmeri Grunow 1915N10 [incl. S. dissectifolium Setchell & Gardner 1917AH76]
S. paniculatum Agardh 1848N10
S. peronii Agardh 1820HS14
S. raoulii Hooker & Harvey 1845L27
S. sagamianumLY96
S. sargasso [incl. Fucus bacciferus, S. bacciferum]BS-V28
S. sinclairii Hooker & Harvey 1845L27
S. spinuligerum Sonder 1845L27
S. swartzii [=Fucus swartzii]BS-V28
S. telephifolium [=Fucus telephifolium]BS-V28
S. thunbergiiKY97
S. tristichumG05
S. variansHK90
S. verruculosum (Mertens) Agardh 1870L27
Sargassum (sect. *Lapazeanum) lapazeanum Setchell & Gardner 1924 [incl. S. bryantii Setchell & Gardner 1924, S. insulare Setchell & Gardner 1924]N10
Sargassum (sect. *Sinicola) sinicola Setchell & Gardner 1924 [incl. S. polyacanthum f. americanum Setchell & Gardner 1924]N10
Sargassum sinicola ssp. camouii (Dawson) Norris & Yensen in Norris 2010 [=S. camouii Dawson 1944, S. sinicola var. camouii (Dawson) Norris & Yensen in Pedroche et al. 2008]N10
*Type species of generic name indicated
References
[AH76] Abbott, I. A., & G. J. Hollenberg. 1976. Marine Algae of California. Stanford University Press.
[BS-V28] Bory de Saint-Vincent, J. B. 1828. Voyage Autour du Monde, Exécuté par Ordre du Roi, Sur la Corvette de Sa Majesté, La Coquille, pendant les années 1822, 1823, 1824 et 1825. Botanique. Cryptogamie. Arthus Bertrand: Paris.
[B79] Buss, L. W. 1979. Habitat selection, directional growth and spatial refuges: why colonial animals have more hiding places. In: Larwood, G., & B. R. Rosen (eds) Biology and Systematics of Colonial Organisms pp. 459–497. Academic Press: London.
[C-SC06] Cavalier-Smith, T., & E. E.-Y. Chao. 2006. Phylogeny and megasystematics of phagotrophic heterokonts (kingdom Chromista). Journal of Molecular Evolution 62: 388–420.
[DH90] Duffy, J. E., & M. E. Hay. 1990. Seaweed adaptations to herbivory. BioScience 40 (5): 368–375.
[G05] Goldberg, N. A. 2005. Temporal variation in subtidal macroalgal assemblages at Black Island, Recherche Archipelago. Journal of the Royal Society of Western Australia 88 (2): 65–71.
[HK90] Huisman, J. M., G. A. Kendrick, D. I. Walker & A. Couté. 1990. The marine algae of Shark Bay, Western Australia. In: Berry, P. F., S. D. Bradshaw & B. R. Wilson (eds) Research in Shark Bay: Report of the France-Australe Bicentenary Expedition Committee pp. 89–100. Western Australian Museum.
[HS14] Huisman, J. M., & A. Sampey. 2014. Kimberley marine biota. Historical data: marine plants. Records of the Western Australian Museum Supplement 84: 45–67.
[KS00] Kawai, H., & H. Sasaki. 2000. Molecular phylogeny of the brown agal genera Akkesiphycus and Halosiphon (Laminariales), resulting in the circumscription of the new families Akkesiphycaceae and Halosiphonaceae. Phycologia 39: 416–428.
[KY97] Kogame, K., & Y. Yamagishi. 1997. The life history and phenology of Colpomenia peregrina (Scytosiphonales, Phaeophyceae) from Japan. Phycologia 36 (5): 337–344.
[L27] Laing, R. M. 1927. A reference list of New Zealand marine algae. Transactions and Proceedings of the New Zealand Institute 57: 126–185.
[LY96] Lee, Y.-P., & S.-Y. Yoon. 1996. Taxonomy of Chondria (Rhodophyta) in Korea. Algae 11 (1): 107–139.
[M88] Markham, J. C. 1988. Descriptions and revisions of some species of Isopoda Bopyridae of the northwestern Atlantic Ocean. Zoologische Verhandelingen 246: 1–63.
[N10] Norris, J. N. 2010. Marine algae of the northern Gulf of California: Chlorophyta and Phaeophyceae. Smithsonian Contributions to Botany 94: 1–276.
[PP64] Peres, J. M., & J. Picard. 1964. Nouveau manuel de bionomie benthique de la mer Mediterranee. Recueil des Travaux de la Station Marine d’Endoume, Bulletin 31 (27): 5–137.
[PA03] Pfister, C. A., & K. L. van Alstyne. 2003. An experimental assessment of the effects of nutrient enhancement of the intertidal kelp Hedophyllum sessile (Laminariales, Phaeophyceae). Journal of Phycology 39: 285–290.
[SRR14] Silberfeld, T., F. Rousseau & B. de Reviers. 2014. An updated classification of brown algae (Ochrophyta, Phaeophyceae). Cryptogamie, Algologie 35 (2): 117–156.
[TS25] Terpis, K. X., E. D. Salomaki, D. Barcytė, T. Pánek, H. Verbruggen, M. Kolisko, J. C. Bailey, M. Eliáš & C. E. Lane. 2025. Multiple plastid losses within photosynthetic stramenopiles revealed by comprehensive phylogenomics. Current Biology 35: 483–499.