A dark red crust, this species is distinct in the northern flora for its production of compact, but free, erect filaments (Image A) arising from a monostromatic basal disc of radiating filaments with prominent cell fusions (Image B). Described from Greenland and with a few known collections from the Canadian Arctic (as Cruoriopsis hyperborea Rosenvinge; Taylor 1962, Lee 1980), we have a single genetically verified specimen from northern Labrador. Reportedly found on a variety of hard substratum the single specimen here was growing on a limpet sibtidally at 6 m.
Possible confusion with Torngatum varicrassum G.W.Saunders could occur. However, in this species the erect filaments appear more strongly coherent, are typically only 1-2 cells long and are limited in their distribution on the crust surface (i.e. the species is predominantly a monostromatic crust). There is also superficial similarity to Rhodophysema elegans (P.Crouan & H.Crouan ex J.Agardh) P.S.Dixon, but this species has cellular fusions between cells of adjacent filaments in both the basal and erect filaments.
Taxonomic Note: Masuda (1976) established the genus Rhodophysemopsis on the basis of a new species, R. laminariae Masuda from Japan, and at that time transferred C. hyporborea to his new genus. However, Masuda does not report cell fusions in the basal layer of R. laminariae, a feature certainly of taxonomic importance in the Palmariales. The generic assignment of R. hyperborea thus remains tentative pending further study of the type, but anatomically is clearly assignable to the Palmariales as is supported by recent molecular data (Evans & Saunders 2017, Saunders et al. 2018).
Image A. View of compact, but free, erect filaments lacking cell fusions, while basal cells are clearly fused (subtidal (6 m) on limpet; N Head of Evans Bight, Torngat, Labrador, NL, 8.9.2014; GWS040281).
Image B. View of cell fusions in basal layer (GWS040281).