Porphyra linearis Greville (A)

Blades forming a dense reddish carpet on upper intertidal rocks at exposed sites just below and merging with Pyropia peggicovensis H.Kucera & G.W. Saunders, the latter dominating upper in the band. A winter to early spring annual. Blades elongate, ovate from a truncate base and tapering at the tip, up to 15 cm tall and 0.5-1.5 cm wide, on a short stipe arising from a small discoid holdfast; olive grayish to reddish basally becoming red toward the tip in females while reproductive males form a white fringe along both margins (Image A). Vegetative cells in surface view near the blade base, cells 15-20 µm wide by 15-30 µm tall, slightly axially elongate and typically paired (Image B). Blades monostromatic, 25-35 µm wide in cross section near the base, vegetative cells taller than wide to isodiametric in shape, at times clearly paired (Image C). Sections of zygotosporangial regions revealed blades 70-80 µm in width with irregular packets of spores (2-4 observed in section view), with fertilization tubes (at times spermatangial remnants) clearly visible (Image D). Sections of spermatangial regions revealed blades 40-65 µm in width with irregular packets of spermatangia (commonly eight observed in section view; Image E). A single putative conchocelis stage was recorded from Folly Cove, MA (GWS017819) in 2010, subtidal (5 m) growing in what appears to be the remnants of a barnacle base on a shell.

Genetically verified gametophytes are confined to exposed locations from Peggys Cove, NS, to southern ME. Other reports have this species extending from Newfoundland to New Hampshire across the Atlantic and throughout Europe (see Mathieson & Dawes 2017, p. 262). Our collections from Peggys Cove are clearly dioecious while literature accounts indicate that this species is monoecious (see Mathieson & Dawes 2017, p. 262) or both (Brodie & Irvine 2003). Indeed early developing spermatangia packages in surface view had initially been confused with developing zygotosporangia in my observations, but sections revealed their true identity as the former rather than the latter. However, some reproductively immature blades nonetheless showed evidence for vertical sectoring, which may correspond to female and male halves (Brodie & Irvine 2003).

Interestingly, despite differences in ITS and rbcL, Porphyra linearis shares COI-5P sequence in common with its close relative Porphyra umbilicalis Kützing consistent with recent introgression between these two species (Image F).

GWS041538-1.jpgImage A. Specimen from exposed mid intertidal at Peggys Cove (GWS041538). Uppermost blade is a male while the lower two blades are females.

GWS041557-0001 copyImage B. Surface view of vegetative cells near blade base (GWS041557).

GWS041557-0006 veg section.jpgImage C. Vegetative section (stained with aniline blue) near the plant base (GWS041557).

GWS041555-0001 Zygo sect.jpgImage D. Section of zygotosporangial development on female thallus (GWS041555).

GWS041557-0007 male sect.jpgImage E. Section of spermatangial development on male thallus (GWS041557).

Figure 1 copyImage F. Comparative data for the markers COI-5P (see text), ITS and rbcL for P. linearis and Porphyra umbilicalis Kützing. Corresponding text and table from a short note that was mothballed (politely rejected by J. Phycol.) are available as pdf files: Saunders 2019; Table S1; as well as a pdf of this figure, Figure 1).