Porphyra purpurea (Roth) C.Agardh (A)

This species has an alternation of heteromorphic generations as is typical in this group. The sporophytes are branched microscopic filaments (Conchocelis stage) and presumably grow in various calcareous substrata (we have no genetically confirmed records to date). The gametophytes are thin and foliose, the blades pinkish to purplish red, oval to elongate, and up to 60 cm in height (Image A). When reproductive, there is a visible line (zipper) down the thallus separating the male and female portions of the blade, which can be observed both macro (Image A) and microscopically (Image B). The latter in surface view reveals a sharp demarcation between the pigmented zygotosporangial (postfertilization female development) and pale yellowish spermatangial (male development) packets (Image B). In vegetative section the blades are monostromatic and 50-65 µm wide, with the cell walls accounting for up to 50 % of the cross sectional width in some specimens (Image C). In surface view the vegetative cells are typically rounded rather than angular in outline (Image D). Cells on the female side are smaller, 10-20 µm, darker in colour and typically paired, while those on the male side are larger, 15-32 µm, paler in colour and more clearly display the stellate plastid with central pyrenoid (Image D). In section the zygotosporangial (Image E) and spermatangial (Image F) packets are easily distinguished, blades in these reproductive regions 55-80 µm wide. As female vegetative cells differentiate to carpogonia (female gametes, which remain in situ on the blade) they acquire a lanceolate shape (Image G).

The gametophyte of this species typically grows in the intertidal on hard substrata, notably rock and shells, but also occasionally on other algae. We have genetically verified records from the Atlantic provinces of Canada, Gulf of St. Lawrence coasts of QC and extending into ME. Individuals of Porphyra umbilicalis Kützing from sheltered areas and or lower in the intertidal can be similar in morphology to Porphyra purpurea,  but the blades are typically more ruffled and rubbery, thicker (>80 µm), more olive-green in colour, and lack vertical segregation (zipper) of the reproductive structures.

Note that there are a number of monostromatic foliose bangiophyte species in the Canadian flora (for the NW Atlantic see Mathieson & Dawes 2017), which can be difficult to identify especially in the absence of reproduction. Definitive identification requires molecular data.

Image A. Two individuals with the blades divided along a distinct line (arrows) into male (right side of blade to the left and left side of blade to the right) and female regions, the former lighter in colour with pale margins and the latter more purplish with mottled margins (low intertidal on rock, Wallace Cove Lighthouse, NB; GWS044419).

Image B. Microscopic view of the ‘zipper’ separating male packets (below) from zygotosporangial packets (above) in a reproductive portion of the blade (GWS044419).

Image C. Cross section of a vegetative portion of the blade displaying the thick walls, and stellate plastids each with a central pyrenoid (GWS044419).

Image D. A surface view of the zipper in a vegetative potion of the thallus with smaller paired female cells above and larger male cells below (GWS044419).

Image E. Section displaying zygotosporangial packet formation near the margin on the female portion of the blade (GWS044419).

Image F. Section displaying spermatangial packet formation near the margin on the male portion of the blade (GWS044419).

Image G. Section at the zipper displaying spermatangial packet adjacent to a female cell differentiating to form a lanceolate carpogonium (GWS044419).