This species presumably has an alternation of heteromorphic generations for which information on the presumably filamentous sporophyte is lacking. Gametophytes are foliose and flaccid, reddish brown in colour and translucent. Blades are sessile lacking a stipe. Blades are round, oval, elongate to irregular in shape and 6-20 cm wide by 8-25 cm tall, and are divided along a line in the thallus (zipper) separating the male and female sectors when reproductive (Image A). In section vegetative regions of the blade are monostromatic, 25-40 µm wide, with each cell containing a single stellate plastid with a central pyrenoid (Image B). In surface view cells of vegetative regions of the thallus are characterized by angular to rounded outlines, 8-25 µm in diam. (Image C).
We have only 2 genetically verified records of this introduced species one each from RI and southern MA, both collected as drift specimens. This may be a relatively rare spring-summer annual. Differing from similar species with sectored female and male blades by its thin thallus 25-40 µm and complete absence of a stipe.
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. Drift specimen with an obvious line (zipper; arrow) separating the female and male (below) sectors of the blade (Narragansett, RI; GWS006042).
Image B. Section (rehydrated) through a vegetative portion of the blade (GWS006042).
Image C. Surface view (rehydrated) of a vegetative portion of the blade (GWS006042).