This red alga presents as a relatively distinct fleshy crust in the Arctic to NW Atlantic flora owing to the pale margins, concentric rings and radial striations on the surface (Image A). Crusts are typically 3-15 cm across and up to 600 µm thick being dark red to brownish centrally becoming pink to yellowish red at the margins (Image A). It is also distinct in these floras owing to the unistratose basal layer, which is subtended by a heavily calcified region, that bears curved ascending simple to sparingly branched erect filaments of rectangular to cuboidal cells to form a compact thallus (Image B). Cells of the basal layer can also produce descending peg-like rhizoids (Image C). Monosporangia, 25-34 by 40-55 µm in dimensions, are produced among 5-7 celled paraphyses in superficial nemathecia suggesting an asexual life history for this species (Image D).
This is the only species of this genus for which we currently have genetically verified records in the Arctic and NW Atlantic. It grows on rock, cobble and shell from the low intertidal and throughout the subtidal (30 m) with genetically verified records from Nome, AK through the Canadian Arctic to ME. Peyssonnelia dubyi P.Crouan & H.Crouan and Peyssonnelia johanseni M.A.Howe are reported in southerly and northerly reaches of the NW Atlantic, respectively (Mathieson & Dawes 2017). Despite extensive DNA barcode surveys from the Arctic through to Rhode Island we have yet to encounter a second species of this genus in this region (specimens preserved in silica would be appreciated).
Image A. Specimen (~3 cm wide) displaying the concentric rings (most obvious at the margins) and radial striations (most obvious mid thallus) that define this species (upper intertidal pool on mussel; Lepreau, NB; GWS014035).
Image B. Vegetative long section (aniline blue stained) displaying the basal layer subtended by a calcified region (subtidal (1 m) on snail; Davis Ln. Beach, Pocologan, NB; GWS041736).
Image C. Closeup of unicellular rhizoid descending from a basal cell (aniline blue stained with calcified layer dissolved; GWS041736).
Image D. Mature nemathecium (aniline blue stained) with large monosporangia produced among multicellular rhizoids (low intertidal on drift mussel shell; Maces Bay, NB; GWS000760).