Large, dark brown to yellowish brown thalli with a short, cylindrical stem that is fastened to rocks by a coarse branching holdfast. The terete primary branches have many simple, Y-shaped proliferations and bear secondary branches that alternate irregularly. Smaller and less numerous oblanceolate leaves, measuring 7 to 15 mm in length and 1.5 to 4 mm in width, with coarsely dentate or serrated margins; midrib is apparent until close to the apex of the thallium. Thallium up to a height of 40 cm