Toothed wrack Fucus serratus, copyright Grubio-1.

Belongs within: Fucales.

The wracks
Published 29 October 2012
Bladder wrack Fucus vesiculosus, from here.

‘Wrack’ is one of those lovely old-fashioned words that doesn’t get used anywhere near as often as it deserves. As well as being an alternative for the word ‘wreck’ (such as in The Wrack of Hesperus), it refers to a number of larger brown seaweeds, including the subjects of today’s post, the Fucaceae.

The Fucaceae are dichotomously branching seaweeds mostly found in the intertidal zone. They vary in size from smaller forms growing higher in the littoral zone (such as the 15-cm-or-less Pelvetia fastigiata) to quite large forms growing lower down (the mid-littoral Ascophyllum nodosum may have fronds two metres in length). Fucaceae are distinguished from other families of brown algae by features such as their well-defined apical and marginal receptacles, and the single four-sided apical cell on each frond (Cho et al. 2006). Fucaceae also differ from some other brown algae in lacking a free-growing haploid stage in their life cycle: haploid cells do undergo a few rounds of post-meiotic mitosis within the receptacles, but are released as individual eggs and sperm that immediately fuse to found the diploid generation.

With the removal of the Australasian Xiphophoraby Cho et al. (2006), the Fucaceae has become a strictly Northern Hemisphere family. This is interesting because the larger clade of the Fucales to which the Fucaceae belong is mostly Southern Hemisphere in diversity. Representatives of the Fucaceae are found both in the Pacific and the Atlantic, with a distinct flora in each (only a single species, Fucus distichus, is believed to be native to both oceans, though some would separate the Pacific population as F. gardneri). Cánovas et al. (2011) favoured a Pacific origin for the Fucaceae, on the grounds that this provided the most intuitive biogeographical connection to the related Australasian taxa Xiphophora and Hormosira, but parsimony analysis alone was unable to confirm or deny this scenario. Basal clades within the family include representatives in both oceans.

The North Pacific Silvetia compressa, photographed by James Watanabe.

Though currently divided between six genera, the family is not speciose, and only two of those genera include more than a single species: the Pacific Silvetia (three species; previously included in Pelvetia but removed by Serrão et al. 1999 on the grounds of non-monophyly) and the mostly Atlantic Fucus (eight[?] species). The clade may be fairly recent in origin: though estimating an age is complicated by the relatively poor fossil record of brown algae, Cánovas et al. (2011) estimated with molecular dating that the Fucaceae diverged in the mid to late Miocene, with their ancestors possibly crossing the equator as Australia moved north. Complicating matters, species of Fucaceae can be morphologically very variable: in the 1960s, for instance, H. T. Powell revised the 100+ species, varieties and forms then recognised within Fucus down to only six species (Serrão et al. 1999). These species can be divided between a northern, specifically cold-water clade with the rockweed Fucus distichus and the toothed wrack F. serratus, and a more warm-water-tolerant clade containing the remaining species (Cánovas et al. 2011). These species tend to be ecologically distinct, each preferring slightly different microhabitats within the littoral zone, but they can hybridise where they come into contact and reproductive isolation is probably not complete (Zardi et al. 2011). Two further species of Fucus have been recognised recently: F. guiryi is a north-eastern Atlantic species previously recognised as F. spiralis var. platycarpus (Zardi et al. 2011; the name ‘Fucus platycarpus‘ cannot be used for this species owing to homonymy), while F. radicans is a species unique to the relatively low-salinity Baltic Sea (Bergström et al. 2005). All indications are that Fucus radicans is a recent segregate from the more widespread bladder wrack F. vesiculosus, which is also the only other Fucus species found in the Baltic. The Baltic Sea itself is not, in its current form, very old, and molecular data suggest that the divergence of F. radicans may have only happened within the last four hundred years (Pereyra et al. 2009).

Knotted wrack Ascophyllum nodosum, from Fisheries and Oceans Canada.
A western rockweed
Published 30 August 2017
Rockweed Silvetia compressa, from here.

Silvetia compressa is a species of the wrack family Fucaceae found on shorelines on the western coast of North America, from British Columbia to Baja California. This species is found in midtidal habitats, generally higher up on the shoreline than other large seaweeds. Individual thalli can reach a maximum length of about three feet (90 cm) but are often smaller. This is a slow-growing species, so patches of Silvetia are slow to recover from damage due to trampling and other disturbance. Please try to avoid walking on the rockweed!

Thalli of Silvetia compressa are composed of thin strands a few millinetres in width with irregular, dichotomous branching. Strands of the thalli lack a midrib (distinguishing them from some other Fucaceae species found in the same area). The width of the strands and regularity of the branching varies with environmental conditions: for instance, individuals growing in locations with stronger wave action have more robust strands that branch more frequently. As with other Fucaceae, the reproductive structures a produced on swollen branch tips called receptacles, but these receptacles do not become inflated with gases and buoyant like those of other species. The exact size and shape of the receptacles is, again, variable.

In many older references, Silvetia compressa may be referred to as Pelvetia fastigiata. The supposed species ‘Fucodium compressum‘ and ‘F. fastigiatum‘ were originally distinguished on the basis that the latter was smaller than the former with more fastigiate branches (that is, the branches remained subparallel). As indicated above, these characters represent the effects of environmental conditions, not fixed differences (Silva 1996). They were eventually included in the genus Pelvetia, together with the Atlantic species P. canaliculata, on the basis of the thalli without a midrib, and the production of just two eggs from each oogonium in the receptacles. However, later analyses supported the separation of the Atlantic and Pacific species of Pelvetia. Not only did they not form a clade in molecular analyses, the eggs in the oogonia were separated by a horizontal division in the Atlantic species but a longitudinal or oblique division in the Pacific species (Silva et al. 2004). As such, the Pacific Pelvetia were transferred into a new genus Silvetia.

Further taxonomic complications involved subspecific variation in Silvetia compressa. A distinctive form of ‘Pelvetia fastigiata‘ found at Pebble Beach in California’s Monterey Bay, with smaller, finer thalli and more abundant, regular branching, was labelled as a separate forma gracilis. Similar individuals were also found on the islands off California’s coast. However, when Silva (1996) examined the original type specimen of P. fastigiata, he discovered that it was an individual of this ‘gracilis‘ form, not the more typical larger form. Later, Silva et al. (2004) examined genetic variation within the Silvetia compressa of California and Baja California. They found that the individuals of the offshore islands were indeed genetically distinct from continental individuals. As well as the differences in growth habit, there was also some difference in receptacle shape: the continental form had receptacles that tended to be linear and pointed whereas those of the island form were ellipsoidal and blunt. However, the island form still could not be labelled with either of the ‘fastigiata‘ or ‘gracilis‘ monikers, as individuals from the type locality of Pebble Beach did not align genetically with insular individuals but with other continental forms. As such, yet another name had to be coined for the insular form which now goes by the name of Silvetia compressa ssp. deliquescens. Let’s see if it sticks this time.

Systematics of Fucaceae
|--Hesperophycus Setchell & Gardner in Gardner 1910SRR14
|--Pycnophycus tuberculatusG64
|--Pelvetiopsis Gardner 1910SRR14
| `--P. linitata (Setchell) Gardner 1913S57
|--Ascophyllum Stackhouse 1809 (nom. cons.)SRR14
| `--A. nodosumSRR14
|--Silvetia Serrão, Cho et al. in Serrão, Alice & Brawley 1999SRR14
| `--S. babingtoniiC-SC06
|--Pelvetia Decaisne & Thuret 1845SRR14
| |--P. canaliculata PP64 [=Fucodium canaliculatumG64]
| `--P. fastigiata (Agardh) DeToni 1895 [=Fucus fastigiatus]S57
| |--M. boryana (Richard) Montagne 1845L27
| `--M. urvilliana Richard 1832L27
| |--F. mackaii [=F. (Ozothallia) mackaii]G64
| `--F. nodosum [=F. (Ozothallia) nodosum]G64
|--Moniliformia Bory de Saint-Vincent 1828BS-V28
| |--‘Fucus’ banskii [=Cystoseira banskii]BS-V28
| |--M. billardierii Bory de Saint-Vincent 1828 [incl. Fucus moniliformis]BS-V28
| `--M. sieberii Bory de Saint-Vincent 1828BS-V28
`--Fucus Linnaeus 1753 (nom. cons.)KC01
|--F. anceps [incl. F. distichus Carruthers 1863 (preoc.), F. furcatus]G64
|--F. edentatus De La Pylaie 1829S57
| |--F. e. f. edentatusS57
| |--F. e. f. acutus Gardner 1922S57
| |--F. e. f. costatus Gardner 1922S57
| |--F. e. f. divaricatus Gardner 1922S57
| `--F. e. f. divergens Gardner 1922S57
|--F. evanescens Agardh 1820S57
| |--F. e. f. evanescensS57
| |--F. e. f. flabellatus Gardner 1922S57
| |--F. e. f. macrocephalus Kjellman 1889S57
| |--F. e. f. magnificus Gardner 1922S57
| |--F. e. f. nanus Kjellman 1877S57
| |--F. e. f. pergrandis Kjellman 1877S57
| |--F. e. f. robustus Setchell & Gardner 1903S57
| `--F. e. f. stellatus Gardner 1922S57
|--F. gardneri Silva 1953S57
| |--F. g. f. gardneriS57
| |--F. g. f. abbreviatus (Gardner) Scagel 1957 [=F. furcatus f. abbreviatus]S57
| |--F. g. f. angustus (Gardner) Scagel 1957 [=F. furcatus f. angustus]S57
| |--F. g. f. contortus (Gardner) Scagel 1957 [=F. furcatus f. contortus]S57
| |--F. g. f. cornutus (Gardner) Scagel 1957 [=F. evanescens f. cornutus, F. furcatus f. cornutus]S57
| |--F. g. f. elongatus (Gardner) Scagel 1957 [=F. furcatus f. elongatus]S57
| |--F. g. f. latifrons (Gardner) Scagel 1957 [=F. furcatus f. latifrons]S57
| |--F. g. f. linearis (Gardner) Scagel 1957 [=F. furcatus f. linearis]S57
| |--F. g. f. nigricans (Gardner) Scagel 1957 [=F. furcatus f. nigricans]S57
| |--F. g. f. reflexus (Gardner) Scagel 1957 [=F. furcatus f. reflexus]S57
| |--F. g. f. rigidus (Gardner) Scagel 1957 [=F. furcatus f. rigidus]S57
| `--F. g. f. variabilis (Gardner) Scagel 1957S57
|--F. membranaceus Gardner 1922S57
| |--F. m. f. membranaceusS57
| `--F. m. f. limitatus Gardner 1922S57
|--F. nodosusBS-V28
|--F. platycarpusS79
|--F. plocaniumD99
|--F. serratusKI02
|--F. siliquosusBS-V28
|--F. spiralisCH97
|--F. vesiculosusG64 [=Halidrys vesiculosusKI02; incl. F. balthicusG64, F. ceranoidesG64, F. inflatusG64]
`--F. virsoidesPP64

*Type species of generic name indicated


Bergström, L., A. Tatarenkov, K. Johanneson, R. B. Jönsson & L. Kautsky. 2005. Genetic and morphological identification of Fucus radicans sp. nov. (Fucales, Phaeophyceae) in the brackish Baltic Sea. Journal of Phycology 41: 1025–1038.

[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.

Cánovas, F. G., C. F. Mota, E. A. Serrão & G. A. Pearson. 2011. Driving south: a multi-gene phylogeny of the brown algal family Fucaceae reveals relationships and recent drivers of a marine radiation. BMC Evolutionary Biology 11: 371.

[CH97] Castro, P., & M. E. Huber. 1997. Marine Biology 2nd ed. WCB McGraw-Hill: Boston.

[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.

Cho, G. Y., F. Rousseau, B. de Reviers & S. M. Boo. 2006. Phylogenetic relationships within the Fucales (Phaeophyceae) assessed by the photosystem I coding psaA sequences. Phycologia 45 (5): 512–519.

[D99] Decandolle, C. 1799. Observations sur les plantes marines. Bulletin des Sciences, par la Societé Philomathique de Paris 1 (22): 171–172.

[G64] Gray, J. E. 1864. Handbook of British Water-weeds or Algae. R. Hardwicke: London.

[KI02] Kawachi, M., I. Inouye, D. Honda, C. J. O’Kelly, J. C. Bailey, R. R. Bidigare & R. A. Andersen. 2002. The Pinguiophyceae classis nova, a new class of photosynthetic stramenopiles whose members produce large amounts of omega-3 fatty acids. Phycological Research 50: 31-47.

[KC01] Kirk, P. M., P. F. Cannon, J. C. David & J. A. Stalpers. 2001. Ainsworth & Bisby’s Dictionary of the Fungi 9th ed. CAB International: Wallingford (UK).

[L27] Laing, R. M. 1927. A reference list of New Zealand marine algae. Transactions and Proceedings of the New Zealand Institute 57: 126–185.

[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.

Pereyra, R. T., L. Bergström, L. Kautsky & K. Johannesson. 2009. Rapid speciation in a newly opened postglacial marine environment, the Baltic Sea. BMC Evolutionary Biology 9: 70.

[S57] Scagel, R. F. 1957. An annotated list of the marine algae of British Columbia and northern Washington (including keys to genera). National Museum of Canada Bulletin 150: 1–289.

[S79] Schuster, R. 1979. Soil mites in the marine environment. Recent Advances in Acarology 1: 593–602.

Serrão, E. A., L. A. Alice & S. H. Brawley. 1999. Evolution of the Fucaceae (Phaeophyceae) inferred from nrDNA-ITS. Journal of Phycology 35: 382–394.

[SRR14] Silberfeld, T., F. Rousseau & B. de Reviers. 2014. An updated classification of brown algae (Ochrophyta, Phaeophyceae). Cryptogamie, Algologie 35 (2): 117–156.

Silva, P. C. 1996. California seaweeds collected by the Malaspina expedition, especially Pelvetia (Fucales, Phaeophyceae). Madroño 43 (3): 345–354.

Silva, P. C., F. F. Pedroche, M. E. Chacana, R. Aguilar-Rosa, L. E. Aguilar-Rosa & J. Raum. 2004. Geographic correlation of morphological and molecular variation in Silvetia compressa (Fucaceae, Fucales, Phaeophyceae). Phycologia 43 (2): 204–214.

Zardi, G. I., K. R. Nicastro, F. Canovas, J. Ferreira Costa, E. A. Serrão & G. A. Pearson. 2011. Adaptive traits are maintained on steep selective gradients despite gene flow and hybridization in the intertidal zone. PLoS One 6 (6): e19402.

Leave a comment

Your email address will not be published. Required fields are marked *