This species forms low brownish to purplish red turfs in the mid intertidal to shallow subtidal. Typically 1-2 (5) cm in height, axes arise from pad-like holdfasts or stolon-like prostrate axes, the blades terete at the base and becoming compressed to flattened near the apices only 140-170 µm thick and 240-500 µm wide with branching sparse and pinnate to irregular (Image A). In whole mount many tips are eroded and blunt, but careful observation of younger tips reveals the single apical cell of this uniaxial species (Image B). Observation of longitudinal sections reveals the central axial filament (Image C), which is surrounded by elongate cells that lend the medulla a filamentous appearance and support the 3-4 layered cortex of secondarily connected cells (Image D).
We only have two genetically confirmed records from RI, both turf forming collections from the low intertidal and subtidal (2.5 m). We also have collections from Ireland and Western Australia in this genetic group indicating that this species has been introduced to many areas owing to human activities.
Image A. Individuals teased apart from a low intertidal turf (~2 cm high) showing the thin basal stolons (arrow) from which additional blades arise and the flattening of the erect axes towards their tips (Kings Beach, RI; GWS042602).
Image B. Closeup of the vegetative tip in whole mount showing the distinct apical cell (GWS042602).
Image C. Long section mid thallus revealing the central axial filament (GWS042602).
Image D. Slightly different focal plane from Image C revealing the elongate cells surrounding the central filament, and 3-4 layered cortex with secondarily pit-connected cells (GWS042602).