Individual thalli arise from typically conical to mound-like holdfasts and can branch low on the thallus along the stipe (Image A). Being a kelp, the species has a distinct stipe and holdfast separated by an easily overlooked transition zone from the strap-like blade, with marginal proliferations forming two distinct rows along the length of the entire thallus (Image B). It is these dense marginal proliferations that give this species its common name of ‘feather boa kelp’. The marginal proliferations can be variable in shape, but typically manifest as small blades, although some develop as pneumatocysts (Image C).
One of the more distinctive species of kelp along the BC coast forming dense stands from the low intertidal into the shallow subtidal (Image D).
Image A. Press of a juvenile producing branches from the stipe (low intertidal on rock, Bamfield, Wizard I., BC; GWS002851).
Image B. Young individual with the stipe distinguished from the flattened blade by the transition zone (intercalary meristem; at the toe of the boot); two rows of marginal proliferations are present along the entire thallus (low intertidal on rock, Palmerston Recreation Reserve near Raft Cove, Vancouver Island, BC; GWS004715).
Image C. Some of the marginal proliferations form pneumatocysts (low intertidal on rock, Pachena Beach, Bamfield, BC; GWS003401).
Image D. Egregia menziesii (Turner) Areschoug dominating the low intertidal kelp at Raspberry Cove, Gwaii Haanas, BC (EGWS000246).