Chordaria chordaeformis (Kjellman) H.Kawai & S.-H.Kim (Ar/A)

This species forms dark brown rarely to unbranched terete thalli, a few to 30+ cm tall (Image A) that are typically gregarious (Featured Image above). Surface cells near the apices are round to angular, 6-14 µm in diameter, with slight spacing and variable in size (Image B). In transverse section of younger axes the assimilatory filaments are weakly clavate and 3-4 cells in length (Image C), and some have a strongly inflated terminal cell (Image D) as was evident in the surface view (Image B). Transverse section of mature axes reveals a solid thallus with the cells small centrally, surrounded by larger cells, which then grade to smaller cells out to the subcortex and outer layer assimilatory filaments (Image E). The assimilatory filaments become 5-7 cells long and more elongate clavate in overall appearance taking on the appearance of paraphyses, although unilocular sporangia were not evident in this collection (Image F).

We have collected this species from Nome, AK, through the Arctic and down into the Maritime provinces of Canada, where it is uncommon. Our collections are all from hard substrata, rocks, cobble, mussels, etc., from the mid intertidal pools to 10 m in the subtidal. Some northerly collections of Chordaria flagelliformis (O.F.Müller) C.Agardh can become sparsely to unbranched and may be confused with Chordaria chordaeformis.

Image A. Press of a collections from the subtidal (6 m) on rock, Button Bay, Churchill, MB (GWS005343).

Image B. View of surface cells near the branch apices (subtidal ( 5 m) on rock, Hogg Island, Torngat, Labrador, NL; GWS039337; rehydrated from press).

Image C. Transverse section highlighting the weakly clavate assimilatory filaments of a vegetative axis (GWS039337; rehydrated from press, aniline blue).

Image D. Close up of inflated terminal assimilatory filament cells (GWS039337; rehydrated from press, aniline blue).

Image E. Transverse section of the solid medulla in an older axis with small cells centrally, transitioning to larger cells and then smaller again into the subcortex (GWS039337; rehydrated from press, aniline blue).

Image F. Transverse section of the clavate assimilatory filaments in an older axis, appearing as paraphyses (post sporangial?) (GWS039337; rehydrated from press, aniline blue).