Dark red to blackish, richly branched thalli (some individuals can be confused for Rhodomela sp.; Image A) growing individually or in clusters from a compact holdfast, with distinct erect axes and individuals 5-30 cm tall. This species can be distinguished from other rhodomelacean species in the NW Atlantic by the thick main axes grading to typically bushy tips (Image A), the strongly alternating branching pattern evident throughout the plant (clearly distichous in younger thallus regions) (Image B). Pericentral cells 16 (8-18), not consistently spirally twisted (may show slight spiraling or wavy appearance in some segments of some individuals, but inconsistent across all, segments) (Image C); cortication thin and incomplete in older regions (Image D), while tips may be heavily invested with trichoblasts (Image E). Tetrasporangial, 70-95 um, produced in a spiral pattern, one per segment (Image F).
Consisting of two genetic groups in the NW Atlantic flora, the first extends from CT to NL and is common in the low intertidal to 20 m subtidal growing on a variety of hard substrata and fleshy algae. The second is more southerly in distribution extending from CT to Cape Breton, NS, but also with genetically verified records from the NE Atlantic, and grows from upper intertidal pools to 8 m subtidal also on a variety of hard substrata and fleshy algae. In view of the two genetic groups assigned to this morphospecies, taxonomic work is needed.
Image A. Richly branched individual superficially appearing like a Rhodomela sp. (Paddys Head, NS; GWS011868).
Image B. Alternate branching pattern evident throughout the thallus (Canso Causeway, NS; GWS032094).
Image C. A view of the pericentral cells upper mid thallus (New River Beach, NB; GWS039121).
Image D. A view of pericentral cells in the low thallus with sparse cortication (GWS039121).
Image E. Trichoblasts at branch apices (GWS039121).
Image F. Tetrahedral tetrasporangia produced in spiral series, one per segment (GWS039121).