Description: Plants ERECT and stiff, 2-20(-30) cm long when reproductive. Plants isolated or in small groups, but occasionally forming low mats, especially in rocky intertidal habitats. Mostly light yellowish brown to dark brown in color when living, but occasionally light grayish or even yellowish white. Holdfast conical or irregular, usually with several unbranched or dichotomously branched stolons growing from basal area of the ERECT axes. Small juvenile plants with flattened leaves. These leaves and the stolons of larger plants can attach to the substratum and initiate new plants. One cylindrical main axis growing from the holdfast. Larger plants often with secondary branching; rarely with higher orders of branching. Leaves with a petiole and a double row of stiff spines around the margin of the leaves in apical view. Petiole cylindrical near base, becoming triangularly compressed in distal portions. Many buy not all plants have some leaves with hollow centers functioning as floats. Receptacles in tight branched clusters, mostly cylindrical, to 1.5 cm long, with rounded blunt apecies; developing in the leaf petiole near the base.