Individuals vary from 30-80 cm in height and have fairly regularly dichotomously divided fronds, which terminate in swollen receptacles when reproductive (Image A). This species is relatively distinctive in our flora owing to the typically regularly paired bladders flanking the obvious midrib (Image B). However, in some habitats the vesicles can be rare/difficult to observe (at times being single and on one side of the midrib only rather than paired) and careful observation may be necessary (Image C).
DNA barcoding with standard markers (COI-5P, rbcL-3P) fails to distinguish between this species and Fucus spiralis Linnaeus (see Kucera & Saunders 2008). Morphological identification can be complicated as well because individuals intermediate in morphology with Fucus spiralis Linnaeus can occur in some locations, as well as in the intertidal where these two species overlap. Further, these species are reported to hybridize, which only further complicates field identification (see Kucera & Saunders 2008, Mathieson & Dawes 2017). Consequently ranges reported here are based on morphological species, but are in need of further study, especially in northern NW Atlantic populations. We have records from ME, throughout Atlantic Canada, extending to Makkovic in Labrador, NL. In the NW Atlantic F. vesiculosus tends to be intermingled with Ascophyllum nodosum (Linnaeus) Le Jolis in the mid intertidal being typically distributed above Fucus distichus Linnaeus and below Fucus spiralis Linnaeus in the intertidal zone. However, it can extend into the lower intertidal and shallow subtidal in some sheltered habitats.
Image A. ‘Typical’ specimen displaying regular dichotomous branching, paired vesicles on the blade flanking the midrib, and tips terminating in swollen reproductive receptacles (low intertidal on rock, Lorneville, NB; EGWS000583).
Image B. Close up view of the paired vesicles on the blade.
Image C. Specimen with few bladders on the blades recalling Fucus distichus Linnaeus (low intertidal on rock, Mispec, NB; (EGWS000660).