Kelp, Bladderwrack, and Other Names for Brown Seaweed

January 12, 2026 •

4 min read

While most people recognize it simply as 'seaweed,' the large group of marine algae belonging to the class Phaeophyceae is also known by many other names, including kelp, bladderwrack, and sargassum. The specific name often depends on the species and its habitat, ranging from giant kelp forests to floating mats in the ocean.

Quick Summary

This article explores the diverse terminology used for brown seaweed, detailing common names like kelp, bladderwrack, and rockweed. It covers different species, their habitats, and distinguishing features, explaining why a single organism has multiple common aliases depending on context and location.

Key Points

Scientific Classification: The scientific name for brown seaweed is Phaeophyceae, a class of multicellular marine algae.
Kelp as an Alias: Large brown seaweeds, especially those of the order Laminariales that form vast underwater forests, are commonly called kelp.
Wrack and Rockweed: Smaller brown seaweeds found on rocky shores in intertidal zones, such as Bladderwrack, are known as wracks or rockweeds.
Sargassum for Floating Species: The genus Sargassum refers to free-floating brown seaweeds that form large mats, particularly in tropical and subtropical waters.
Culinary Names: In cuisine, specific brown seaweeds have distinct names, such as kombu (a type of kelp) and hijiki (a type of sargassum).
Structural Variations: Different names often reflect differences in structure, from the large stipes and blades of kelp to the fronds and paired air bladders of wracks.

The Scientific and Common Names of Brown Seaweed

Brown seaweed, a member of the class Phaeophyceae, is a diverse group of marine algae with over 1,500 species globally. This taxonomic class is the scientific basis for all brown seaweeds, but many common names are used to describe the various types based on their morphology, habitat, and region. Understanding this varied terminology is key to navigating the world of marine biology and edible sea vegetables.

Kelp: The Giant Brown Seaweeds

Kelp is one of the most widely recognized names for a group of large brown seaweeds, especially those within the order Laminariales. These are known for their massive size and the dense underwater 'forests' they form, which are crucial ecosystems for numerous marine species. Different species of kelp have their own common names:

Giant Kelp (Macrocystis pyrifera): The largest of all algae, known for its rapid growth.
Sugar Kelp (Saccharina latissima): Known for its sweet, umami flavor and used in culinary applications like kombu.
Bull Kelp (Nereocystis luetkeana): Characterized by a single, large gas bladder that keeps its blade afloat.
Oarweed (Laminaria digitata): Found on rocky coastlines and an important source of alginates.

Wracks: The Intertidal Brown Algae

'Wrack' is a common term for brown seaweeds belonging to the order Fucales, typically found in intertidal zones and on rocky seashores. These species are well-adapted to being exposed to the air during low tide.

Bladderwrack (Fucus vesiculosus): Recognizable by its paired, gas-filled bladders that provide buoyancy. It is also sometimes simply called kelp.
Knotted Wrack (Ascophyllum nodosum): Has long, leathery fronds with characteristic ovoid air bladders.
Serrated Wrack (Fucus serratus): Easily identified by its flat, serrated fronds.
Channelled Wrack (Pelvetia canaliculata): Lives higher on the shore and can tolerate low moisture conditions.

Sargassum: The Floating Brown Seaweed

Another name for brown seaweed is sargassum, a genus known for forming huge, free-floating mats in the open ocean, most famously in the Sargasso Sea. Unlike most other brown seaweeds, sargassum can be pelagic, or unattached to the seabed, and drifts with ocean currents. These floating mats provide a vital habitat for many marine creatures. Hijiki is a specific type of sargassum known in Japanese cuisine.

Regional and Specific Aliases

In addition to the main categories, many brown seaweeds have regional or specific names based on their appearance or culinary use. For example, the thongweed (Himanthalia elongata) is sometimes called 'sea spaghetti' for its long, strap-like fronds. Other examples include dulse (Palmaria palmata), although this is a red seaweed, and carrageen (Chondrus crispus), also a red seaweed, but often mentioned in the same context as edible types. While these are not brown seaweeds, their common mention illustrates the rich and often complex naming conventions for marine algae.

Comparison of Common Brown Seaweed Types


Feature	Kelp (Laminariales)	Wrack (Fucales)	Sargassum
Habitat	Primarily cooler, nutrient-rich coastal waters.	Intertidal zones and rocky shores.	Subtropical and tropical waters, often free-floating.
Size	Can grow to lengths of over 50 meters, forming large forests.	Typically smaller, ranging from centimeters to around 2 meters.	Variable in size, forming large mats of seaweed.
Structure	Differentiated into a holdfast, stipe, and blades; often has gas bladders.	Differentiated thallus, often with midribs and paired gas bladders (pneumatocysts).	Complex, branched thallus with leafy appendages and many small gas bladders.
Key Use	Food (kombu), alginate extraction, habitat for marine life.	Food (traditionally), alginate source, some cosmetic uses.	Habitat for open-ocean life, traditional medicine.

Conclusion: A World of Names

In conclusion, asking "What is another name for brown seaweed?" opens up a fascinating exploration of marine biology. While the scientific class is Phaeophyceae, the popular terminology varies greatly, with 'kelp' referring to large species in colder waters, 'wrack' describing those in intertidal zones, and 'sargassum' distinguishing the free-floating, tropical varieties. These different names reflect not just regional vernacular but also important ecological distinctions, highlighting the diversity within this significant group of marine algae. The next time you see brown seaweed, you'll know that its true identity may be more specific than you first imagined.

The Importance of Identification

Accurate identification of brown seaweed is important not only for scientific classification but also for its various practical applications. For example, specific species are cultivated for their unique flavor profiles for food, while others are harvested for valuable compounds like alginates, used as thickeners in many commercial products. Incorrectly identifying a species could lead to a less-than-optimal culinary or industrial outcome. Furthermore, understanding the specific types of brown seaweed, such as the difference between edible kelp and floating sargassum, is essential for comprehending marine ecosystems.

Frequently Asked Questions

No, not all brown seaweed is called kelp. Kelp refers specifically to a group of large, brown seaweeds in the order Laminariales. While kelp is a brown seaweed, the term brown seaweed also includes other types like wracks and sargassum.

Bladderwrack (Fucus vesiculosus) is a type of brown seaweed, or wrack, that is common on the rocky shores of the North Atlantic. It is characterized by its paired, gas-filled bladders and prominent midrib on the fronds.

The name sargassum was given by Portuguese sailors who observed the floating macroalgae in the Sargasso Sea. They named it after the wooly rock rose (Halimium lasianthum), which was called sargaço in Portuguese.

Yes, brown seaweed is a type of algae, specifically belonging to the class Phaeophyceae. It is a multicellular marine alga, distinct from microscopic, single-celled algae.

Seaweed is generally categorized into three main color groups based on their dominant pigments: red algae (Rhodophyta), green algae (Chlorophyta), and brown algae (Phaeophyceae).

The characteristic brown or olive-green color of brown seaweed is due to the presence of a golden-brown xanthophyll pigment called fucoxanthin, which masks the green chlorophyll.

Yes, kelp includes some of the largest species of seaweed, with giant kelp (Macrocystis pyrifera) capable of reaching lengths of over 50 meters, making it the largest of all algae.