UC specimens and range limits for Fucus distichus

• Blue markers: specimen records
• Yellow marker: type locality, if present
• Red markers: endpoints of range from literature

View map from the Consortium of Pacific Northwest Herbaria

Notes: From Unalaska Island, Aleutian Islands, Alaska to Government Point, Santa Barbara Co. Also on both sides of the Atlantic Ocean.

Laughinghouse et al. (2015) studied haplotypes of F. distichus across the Arctic -- but California specimens were not included in their analyses, nor are subspecies currently recognized (Coyer et al. 2006). Further, California Fucus occur in the upper to mid intertidal, not lower intertidal, as they characterize it. They state:

"Northern hemisphere rockweeds (Fucus) are thought to have evolved in the North Pacific and then spread to the North Atlantic following the opening of the Bering Strait. They have dispersed and widely speciated in the North Atlantic and its tributary seas. Fucus distichus is likely the most ancestral member of this genus, and studies have shown that there are several species/subspecies in this complex (i.e. F. evanescens and F. gardneri). We used phylogenetic and haplotype analyses to test the phylogenetic placement, biogeography, and ancestral state of F. distichus. Our data and subsequent analyses demonstrate that, unlike previous studies which lacked an extensive geographical area of arctic and subarctic samples, there is a distinct arctic haplotype that is the source of subspecies haplotypes in both the North Pacific and North Atlantic. F. distichus occupies a low tide zone habitat, and in arctic/subarctic regions it must be adapted to the severe stress of sea ice coverage and disturbance of many months per year. We hypothesize that the very large geographic area of arctic and subarctic rocky shores available to this species during interglacials, supported by large arctic/subarctic fringe areas as well as unglaciated refugia provides a robust population and gene pool during glacial cycles (described by the Thermogeographic Model). This gene pool dilutes that of the more fragmented and area-limited Temperate/Boreal area populations when they are brought together during glacial cycles. We suggest that similar subspecies complexes for a variety of Arctic/Subarctic shore biota should be examined further in this context, rather than arbitrarily being split up into numerous species." (http://journals.plos.org/plosone/article/asset?id=10.1371/journal.pone.0143795.PDF)

Status: Despite higher species richness in the genus Fucus in the North Atlantic, a gradient of decreasing haplotype and nucleotide diversities (using two mitochondrial markers) in F. distichus from the North Pacific to the East Atlantic supports a North Pacific origin (Coyer et al. 2006). Molecular studies (mitochondrial markers, ITS, CO1 sequences) have established that Fucus distichus is the native member of the genus in California (Coyer et al. 2006, Kucera & Saunders 2008). The morphology of F. distichus varies tremendously depending on habitat.

Habitat: Upper intertidal in relatively sheltered environments

Life History: Diplontic, with gametic meiosis; monoecious

Search Sequences in GenBank

Fucus Linnaeus 1753

Thalli perennial, with disk-shaped or irregularly shaped holdfast. Erect portion of thallus dichotomously branched, flattened, with more or less distinct percurrent midrib; gas-filled pneumatocysts of definite form sometimes present, in pairs lateral to midrib; erect portion also bearing cryptostomata and caecostomata. Base of thallus becoming stipelike through abrasion of tissues lateral to midrib. Gametangia developed in conceptacles embedded at apices of final dichotomies. Plants monoecious or dioecious.

Fucus distichus L.

Linnaeus 1767: 716; Turner 1808: 7.

The type subspecies, not known from the Pacific, differs from subsp. edentatus in its relatively smaller size, delicate structure, and narrow blades.

Fucus distichus subsp. edentatus (de la Pyl.) Pow.

Fucus edentatus de la Pylaie 1829: 84. F. distichus subsp. edentatus (de la Pyl.) Powell 1957a: 424 (incl. synonymy); Hollenberg & Abbott 1966: 31 (incl. synonymy).

Thalli 10-25 cm tall, rarely taller, regularly dichotomous, the divisions 1.5-2.5 cm broad, the thalli with prominent midrib in older portions, olive brown to dark brown; receptacles broadening at apices in most specimens, often constituting one-fourth to one-third length of mature thallus, swollen at reproductive maturity; plants monoecious.

Abundant in upper intertidal and midtidal, on rocks, sometimes growing mixed with Hesperophycus (which it resembles), N. Wash. to Pt. Conception, Calif. Also N. Atlantic. Type locality: Newfoundland.

Fucus distichus subsp. edentatus f. abbreviatus (Gardn.) Hollenb. & Abb.

Fucus furcatus f. abbreviatus Gardner 1922: 19. F. distichus subsp. edentatus f. abbreviatus (Gardn.) Hollenberg & Abbott 1966: 31 (incl. synonymy).

Thalli 10-15(25) cm tall, regularly dichotomous, with divisions 0.3-1 cm broad, with prominent midrib below, olive brown to dark brown; receptacles mostly tapering to acute apices, constituting half or more of length of mature thallus; caecostomata abundant; conceptacles numerous, prominent.

Locally common, discontinuously distributed, saxicolous, upper intertidal, Waldron I. (San Juan Co.; type locality), Wash., to Carmel River (Monterey Co.), Calif.

Excerpt from Abbott, I. A., & Hollenberg, G. J. (1976). Marine algae of California. Stanford University Press, Stanford, California. xii [xiii] + 827 pp., 701 figs.

Notes: In California, this species is now considered to be Fucus distichus. See Distribution notes.