Coccotylus brodiei (Turner) Kützing (Ar/A)

Thalli consist of clumps of individual fronds, ranging in size from 1-16 cm tall (smaller individuals are commonly field identified as Erythrodermis traillii (Holmes ex Batters) Guiry & Garbary), that have terete stipes below, but which become flattened to almost blade-like above, and account for 50-70% of the overall height of each frond (Image A). In part the apparent flattened portions of the stipe derive from the regeneration of new blades from the margins of eroded blades, yielding compound thalli (Image B). Terminal bladed portions are highly variable in shape and size. In transverse section near their apices the bladed regions are 120-200 µm thick consisting of 2-6 layers of variable (35-100 µm; the largest typically axially compressed, i.e. wider than tall) medullary cells that gradually reduce in size to a 1-2 layered inner cortex and ultimately an outer cortex of 1-2 layers lacking an anticlinal appearance (Image C). Terete regions of the stipe are 400-900 µm wide and composed of many layers of medullary cells that are variable in size, typically 10-35 µm in diameter, and surrounded by a relatively thick cortex of anticlinally arranged cells (Image D). In some individuals distinctive cells of the cortex and medulla of the stipe were filled with darkly staining contents appearing as storage or gland cells, but their purpose remains uncertain (Image E). This species reproduces by the production of carpotetrasporangia formed in cystocarps on the gametophyte generation (a free living sporophyte generation is lacking in the life history) at the termini of the blades (Image F).

We have genetically verified records from upper intertidal pools to the subtidal (14 m) ranging from CN to the island of NL, but also with one specimen from Churchill, MN (GWS005240), as well as collections from Europe. In general terms Coccotylus brodiei is more common to the south in the NW Atlantic while Coccotylus truncatus (Pallas) Wynne & Heine extends through the Canadian Arctic into the Bering Sea preferring northerly waters and being typically subtidal in its southern range. The stipes in Coccotylus brodiei also contribute more (50-70%) to the overall length of individual fronds than in Coccotylus truncatus (Pallas) Wynne & Heine (20-50%). Definitive identification requires molecular work. Species of Coccotylus are easily confused with some individuals of Phyllophora pseudoceranoides (S.G.Gmelin) Newroth & A.R.A.Taylor, but stipes in the latter are typically terete throughout their length only expanding as they form the cuneate bases of the blades and they typically account for 70-90% of the overall height of individual fronds. Further, cystocarps in Phyllophora pseudoceranoides (S.G.Gmelin) Newroth & A.R.A.Taylor are formed along the stipe, not at the blade termini, and contain carposporangia, while the tetrasporangia are formed in sori on a separate diploid generation, i.e. there is an alternation of isomorphic generations. Vegetative individuals of intermediate morphology should be confirmed with molecular data. Coccotylus brodiei can be highly variable in morphology, some of which is recorded in the BOLD taxonomy browser.

GWS003088.jpgImage A. ‘Typical’ specimen in that portions of the stipe become notably flattened; from a tide pool in the mid upper intertidal zone on Grand Manan, NB (GWS003088; press).

GWS006916.JPGImage B. Close-up of a pressed specimen with blades derived from the eroded margins of older blades to yield compound thalli and contribute to the flattened appearance of the stipe (mid intertidal on rock, Cape St. Marys, NS; GWS006916).

GWS017873-0001.jpgImage C. Transverse section of an ultimate blade (mid thallus) (subtidal (5m), Woodshole, MA; GWS017873; rehydrated from press; aniline blue stained).

GWS017873-0002.jpgImage D. Transverse section of the terete region of a stipe (GWS017873; rehydrated from press; aniline blue stained).

GWS017873-0004.jpgImage E. Close-up of the darkly staining cells in the medulla and cortex of Image C (GWS017873; rehydrated from press; aniline blue stained).

GWS006922a.JPGImage F. Close-up of the carpotetrasporoblastic cystocarps on a pressed mid intertidal specimen from Cape St. Marys, NS (GWS017873).