This species has an alternation of heteromorphic generations for which information on the presumably filamentous sporophyte is lacking. Gametophytes are foliose and flaccid, ranging from pale brown to reddish brown to dark purplish brown in colour and translucent. Blades are round, oval to irregular in shape and 6-30 cm wide by 5-24 cm tall, and are divided along a line in the thallus (zipper) separating the male and female sides when reproductive (Image A). In section vegetative regions of the blade are monostromatic, 45-80 µm wide with squat cells, 20-26 by 33-45 µm, each containing a single (at times 2?) stellate plastid with a central pyrenoid (Images B & C). In thicker regions of the blade the walls tend to dominate the width of the section (Image C). In surface view cells of vegetative regions of the thallus are characterized by angular to rounded outlines, 15-30 µm in diam. (Image D).
We have ~30 genetically verified records of this species, mostly from the Maritime Provinces, Canada, with a single specimen from NL. Individuals were collected from the upper intertidal to slightly subtidal (1.5 M), typically on rock, but also on other hard substrata and, rarely, coarse algae. This appears to be a relatively rare summer-fall annual. Differing from similar species with sectored female and male blades by the development of the spermatangial and zygotosporangial packages along the entire outer margin to the base of the thallus. Definitive identification, especially for non-productive individuals, requires molecular data.
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. Specimen with clear divisions into male (spermatangial packets; below) and female (zygotosporangial packets; above) from the low intertidal on mussel (Letete exposed biodiversity site, NB; GWS032193).
Image B. Vegetative cross section displaying cells with stellate plastids containing a central pyrenoid (mid intertidal on rock, Wallace Cove Lighthouse, NB; GWS031525).
Image C. Vegetative cross section revealing thick cell walls (mid intertidal on rock, Baxter’s Harbour, Bay of Fundy, NB; GWS044438).
Image D. Vegetative cells in surface view are angular to rounded in outline (from rehydrated material) (low intertidal on rock, Letete exposed biodiversity site, NB; GWS032190).