This species is highly variable in morphology ranging from densely branched plants with thin axes bringing to mind species like Polysiphonia sensu lato (Image A) to plants more reminiscent of the classic view of Rhodomela lycopodioides (Linnaeus) C.Agardh in the Canadian Arctic (Image B). Thalli are uniaxial with an obvious, rounded apical cell, and although construction is polysiphonous, this is obscured by a cortical covering in whole mount. Cross sections in mature thallus regions reveal the distinct central rosette pattern of this species, which consists of a central axial filament, 75-100 µm in diam., surrounded by 6(-8) periaxial cells of similar dimensions (Image C). The central rosette is surrounded by a ring or two of smaller, 15-25 µm wide and 25-30 µm long (perpendicular to the central axial filament), brick-like inner cortical cells that help to distinguish the central rosette from the surrounding cortical tissue (Image C). Long section also reveals the sharp transition from the periaxial cells to the rectangular inner cortical cells, 15-25 µm wide, 25-30 µm long and 150-300 µm tall (parallel to the central axial filament) (Image D).
Genetically verified records extend from Nome, AK through the Arctic to the northern Gulf of Saint Lawrence (QC and NL). Collected from mid intertidal pools to subtidal (5 m) on various hard substrata and coarse algae. This species overlaps in range with Rhodomela lycopodioides (Linnaeus) C.Agardh, Rhodomela sibirica A.Zinova & Vinogradova and Rhodomela virgata Kjellman. It differs from all of these in that the axial cell is much larger when viewed in cross section of older thallus regions (75-100 µm versus ~40-60 µm). Rhodomela sibirica A.Zinova & & Vinogradova has fewer branching orders (3-5), while Rhodomela lycopodioides (Linnaeus) C.Agardh lacks a clear central rosette in many cross sections. Rhodomela virgata Kjellman is typically found deeper in the subtidal.
Image A. Specimen with a resemblance to various Polysiphonia spp. found drift at St. Irénée, QC (GWS008075).
Image B. Specimen collected in the field and incorrectly identified as Rhodomela lycopodioides (Linnaeus) C.Agardh from the subtidal (3 m) on rock at Nome, AK. (GWS041950).
Image C. Cross section of a mature thallus region displaying the central axial (A), periaxial (P) and inner brick-like layer or two of cortical cells (C) (low intertidal on mussel, Churchill, MB; GWS005571).
Image D. Long section (aniline blue stained) of a mature thallus region displaying the central axial (A), periaxial (P) and inner brick-like layer or two of cortical cells (C) (subtidal on rock, St. Davids, NL; GWS007342).