Sporangial thalli (to 2.3 m tall) perennial,the holdfast composed of stout, branched haptera. Stipe long (to 1.5 m), erect, unbranched, cylindrical in basal portion, flattened in upper portion (4 cm broad), woody in texture and with concentric rings in cortex. Stipe terminating in single lanceolate blade (to 80 cm long, 10 cm broad), without midrib, but with axial portion slightly thickened, surface of blade smooth. SAMPLING CODE NOTES: PTCA = Adult stipe >= 30 cm; PTCR = Recruit stipe < 30 cm; PTHO = Holdfast.

Fertile usually in October. Terminal blade and sporophylls shed in winter. Saxicolous, forming large, widespread beds.

Subtidal 7 to 20 m; British Columbia, Canada to Baja California, Mexico.