Euthora cristata (C.Agardh) J.Agardh (BC/Ar/A)

This species can be highly variable in morphology ranging from an irregularly and proliferously branched flattened thallus (Image A) to wiry individuals superficially more reminiscent of something in the Ceramiales (Image B) such as broader plants of the Pantoneura morphology of Membranoptera fabriciana (Lyngbye) M.J.Wynne & G.W.Saunders. Whereas branches in M. fabriciana and other wiry Ceramiales terminate in obvious apical cells, E. cristata can be more difficult to interpret with some tips appearing to have multiple terminal cells (Image C) while other tips (even on the same individual) can have a single terminal cell (Image D). Regardless, the medulla of E. cristata, at least in the NW Atlantic and Arctic (some Callophyllis sp. and E. timburtonii B.E.Clarkston & G.W.Saunders in BC can be confused with E. cristata; Clarkston & Saunders 2010), is distinct from all other species with its chains/clusters of small cells intermingled among the larger cells of the medulla (Image E). Tetrasporangia, scattered throughout the cortex near the plant apices, can be observed in whole mount (Image F), and are irregularly cruciate in division being 16-24 µm wide by 23-34 µm long (Image G). We have genetically verified individuals from the low intertidal to subtidal (30 m) growing on a wide variety of hard substrata and other algae. Our verified collections come from Kamchatka, the San Juan Islands, WA, Haida Gwaii, BC, through locations in the Canadian Arctic and Atlantic provinces south to MA, USA, and from Norway – a true circumpolar species. GWS011849.JPGImage A. Typical flattened morphology of low intertidal to shallow subtidal specimens; from Paddys Head, NS (GWS011849). GWS007218.jpgImage B. Deep subtidal (20 m on rock) wiry morphology from Bonne Bay, NL (GWS007218). G003-0001 copy.jpgImage C. Whole mount of a tip lacking a distinct apical cell in a specimen from Lepreau, Bay of Fundy, NB (G1003). G1003(40X)001 copy 2.jpg Image D. Whole mount showing single apical cell (G1003). G1003(20X)001 copy 2.jpgImage E. Transverse vegetative section showing smaller, slightly pigmented to unpigmented, cells among larger medullary cells (G1003).
Image F. Tetrasporangia visible in whole mount of a branch tip (subtidal (2 m) on Phyllophora pseudoceranoides (S.G.Gmelin) Newroth & A.R.A.Taylor ex P.S.Dixon & L.M.Irvine, Mispec Beach north (near LNG terminal), NB; GWS047426).
Image G. Irregularly cruciate tetrasporangium (GWS047426).