Seaweeds in general have three major parts: holdfast, stipe, and blade. When referring to an entire plant and all of its parts, we call it a thallus.

Holdfast: This anchors the seaweed to the substrate.

Stipe (st-eye-p): This stem-like structure connects the blade to the holdfast. The stipe is very flexible which allows the seaweed to flex and bend with wave action. This flexibility prevents it from being ripped loose from the rock.

Blade: This is the largest part of the thallus. It is the blade that is responsible for photosynthesis and most of the nutrient absorbtion.

Vesicles (vess-ah-culls): Commonly called air or gas bladders, these balloon-like structures provide buoyancy to the seaweed blade when it is submerged. By causing the blade to float, the algae is able to stay at the surface for maximum sunlight exposure. The air or gas inside the bladder is mostly nitrogen with varying amounts of oxygen, carbon dioxide and water vapour. These gases are not trapped inside the bladders but actually diffuse in and out. Not all seaweeds have vesicles. It has also been observed that Fucus species that grow in high wave action areas rarely develop air bladders.

Receptacles: The swollen tips of Fucus species and Ascophyllum nodosum become receptacles in the spring. The swollen receptacles produce reproductive gametes, eggs and sperm, and release them into the water.