Erythrodermis traillii (Holmes ex Batters) Guiry (A)

Blades are simple, to once (twice or more) di(tri)chotomously to irregularly branched, and are attached by a small discoid holdfast (Images A-C). Individuals blades are borne on a short and very narrow (<1 mm) stipe, and are lanceolate to oblong, heart-shaped or irregular in outline being 1-2(3) cm tall and typically only 2-5 mm wide (Image B). Tips and margins can produce small proliferations that can grow into additional blades or terminate with cystocarps (Image C).

In long section mid thallus, blades are only 90-100 µm wide; medullary cells are isodiametric to weakly axially elongate 20-45 µm wide and 30-65 µm tall and typically of 2-3 layers, which have notably thickened walls (5-8 µm); inner cortical cells typically form a single layer of axially flattened cells 10-15 µm wide and 4-8 µm tall; with a complete outer cortex of two(+) layers, the cells relatively isodiametric in outline and 3-7 µm in diameter (Image D). In transverse section upper mid thallus the cells are typically rounder in outline in the medulla, and blades were thinner, 80-85 µm, in width, but the thick walls of the medullary cells and the two-layered complete cortex remain evident (Image E).

In the NW Atlantic this species can be confused with Rhodymenia delicatula P.J.L. Dangeard. In that species the blades are typically more linear; in longitudinal section the medullary cells tend to be more axially elongate with less pronounced cell walls, and the outer cortical cells typically form a single incomplete layer and are axially flattened.

We have genetically verified collections from CN to southern NL (as well as Norway), typically lowest intertidal to subtidal (15 m) growing on rock walls or underhangs as small localized clumps or sparse turfs. This species has an alternation of heteromorphic generations and the observations here are restricted to the upright gametophyte. We have not yet encountered the crustose sporophyte in our genetic surveys.

OLYMPUS DIGITAL CAMERAImage A. Blades collected on a subtidal (5 m) rock wall at Peggys Cove, NS (GWS031217).

GWS013891.JPGImage B. Close-up of simple blades for a collection from a low intertidal rock wall on Campobello I., NB (GWS013891). Scale = mm ruler.

GWS005618.JPGImage C. Irregularly branched individuals with cystocarps for a collection from a low intertidal rock wall in southern ME (GWS005618). Scale = mm ruler.

GWS013891-0004 copy.jpgImage D. Longitudinal section (aniline blue) mid thallus (GWS013891).

GWS013891-0005 copy.jpgImage E. Transverse section (aniline blue) upper mid thallus (GWS013891).