Macrocystis tenuifolia

Giant kelp

Authority: Postels & Ruprecht

Thallus of this golden brown canopy kelp may reach a length of 30 m (99 ft). A conical, richly branched holdfast (haptera) hosts several stipes, which branch dichotomously into vine-like fronds with blades to ~ 50 cm (20 in) long at regular intervals. The blades, which develop via splitting of a small terminal blade, are distinctly wrinkled with marginal teeth and a small gas-filled float (pneumatocyst) at their base. Some thalli, particularly in British Columbia and Washington, have a flattened, creeping, rhizome-like holdfast; this form was previously identified as M. integrifolia.