Brown algae (singular: alga), comprising the

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

Phaeophyceae, are a large group of

multicellular A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially un ...

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

, including many seaweeds located in colder waters within the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

. Brown

are the major

seaweeds Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

of the temperate and polar regions. They are dominant on rocky shores throughout cooler areas of the world. Most brown algae live in marine environments, where they play an important role both as food and as a potential

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

. For instance, ''

Macrocystis ''Macrocystis'' is a monospecific genus of kelp (large brown algae). This genus contains the largest of all the phaeophyceae or brown algae. ''Macrocystis'' has pneumatocysts at the base of its blades. Sporophytes are perennial and the indi ...

'', a

kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwa ...

of the order

Laminariales Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underw ...

, may reach in length and forms prominent underwater

kelp forest Kelp forests are underwater areas with a high density of kelp, which covers a large part of the world's coastlines. Smaller areas of anchored kelp are called kelp beds. They are recognized as one of the most productive and dynamic ecosystems on Ea ...

s. Kelp forests like these contain a high level of biodiversity. Another example is ''

Sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae ( seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral ...

'', which creates unique floating mats of seaweed in the tropical waters of the Sargasso Sea that serve as the habitats for many species. Many brown algae, such as members of the order

Fucales The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebaseref name="Guiry and Guiry">Guiry, M.D. and ...

, commonly grow along rocky seashores. Some members of the class, such as kelps, are used by humans as food. Between 1,500 and 2,000

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of brown algae are known worldwide. Some species, such as ''

Ascophyllum nodosum ''Ascophyllum nodosum'' is a large, common cold water seaweed or brown alga (Phaeophyceae) in the family Fucaceae, being the only species in the genus ''Ascophyllum''. It is a seaweed that only grows in the northern Atlantic Ocean, also known in ...

'', have become subjects of extensive research in their own right due to their commercial importance. They also have environmental significance through carbon fixation. Brown algae belong to the group

Heterokont Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...

ophyta, a large group of

eukaryotic Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...

organisms distinguished most prominently by having chloroplasts surrounded by four membranes, suggesting an origin from a

symbiotic relationship Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

between a basal eukaryote and another eukaryotic organism. Most brown algae contain the pigment

fucoxanthin Fucoxanthin is a xanthophyll, with formula C42H58O6. It is found as an accessory pigment in the chloroplasts of brown algae and most other heterokonts, giving them a brown or olive-green color. Fucoxanthin absorbs light primarily in the blue-green ...

, which is responsible for the distinctive greenish-brown color that gives them their name. Brown algae are unique among heterokonts in developing into multicellular forms with differentiated tissues, but they reproduce by means of flagellated

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s and

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s that closely resemble cells of other heterokonts. Genetic studies show their closest relatives to be the

yellow-green algae Yellow-green algae or the Xanthophyceae (xanthophytes) are an important group of heterokont algae. Most live in fresh water, but some are found in marine and soil habitats. They vary from single-celled flagellates to simple colonial and filamento ...

Morphology

Brown algae exist in a wide range of sizes and forms. The smallest members of the group grow as tiny, feathery tufts of threadlike

cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...

s no more than a few centimeters (a few inches) long. Some species have a stage in their life cycle that consists of only a few cells, making the entire alga microscopic. Other groups of brown algae grow to much larger sizes. The rockweeds and leathery

s are often the most conspicuous algae in their habitats. Kelps can range in size from the sea palm ''

Postelsia ''Postelsia palmaeformis'', also known as the sea palm (not to be confused with the southern sea palm) or palm seaweed, is a species of kelp and classified within brown algae. It is the only known species in the genus Postelsia. The sea palm is ...

'' to the giant kelp '' Macrocystis pyrifera'', which grows to over long and is the largest of all the algae. In form, the brown algae range from small crusts or cushions to leafy free-floating mats formed by species of ''

''. They may consist of delicate felt-like strands of cells, as in ''

Ectocarpus ''Ectocarpus'' is a genus of filamentous brown alga that is a model organism for the genomics of multicellularity. Among possible model organisms in the brown algae, ''Ectocarpus'' was selected for the relatively small size of its mature thallu ...

'', or of flattened branches resembling a fan, as in '' Padina''. Regardless of size or form, two visible features set the Phaeophyceae apart from all other algae. First, members of the group possess a characteristic color that ranges from an

olive green Olive is a dark yellowish-green color, like that of unripe or green olives. As a color word in the English language, it appears in late Middle English. Shaded toward gray, it becomes olive drab. Variations Olivine Olivine is the typica ...

to various shades of

brown Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing or painting, brown is usually made by combining the colors orange and black. In the RGB color model us ...

. The particular shade depends upon the amount of

present in the alga. Second, all brown algae are

. There are no known species that exist as single cells or as colonies of cells, and the brown algae are the only major group of

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

s that does not include such forms. However, this may be the result of classification rather than a consequence of evolution, as all the groups hypothesized to be the closest relatives of the browns include single-celled or colonial forms. They can change color depending on salinity, ranging from reddish to brown.

Visible structures

Whatever their form, the body of all brown algae is termed a ''

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...

'', indicating that it lacks the complex

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

and

phloem Phloem (, ) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This transport process is c ...

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

s. This does not mean that brown algae completely lack specialized structures. But, because some botanists define "true" stems, leaves, and roots by the presence of these tissues, their absence in the brown algae means that the stem-like and leaf-like structures found in some groups of brown algae must be described using different terminology. Although not all brown algae are structurally complex, those that are typically possess one or more characteristic parts. A '' holdfast'' is a rootlike structure present at the base of the alga. Like a root system in plants, a holdfast serves to anchor the alga in place on the ''substrate'' where it grows, and thus prevents the alga from being carried away by the current. Unlike a root system, the holdfast generally does not serve as the primary organ for water uptake, nor does it take in nutrients from the substrate. The overall physical appearance of the holdfast differs among various brown algae and among various substrates. It may be heavily branched, or it may be cup-like in appearance. A single alga typically has just one holdfast, although some species have more than one stipe growing from their holdfast. A '' stipe'' is a stalk or stemlike structure present in an alga. It may grow as a short structure near the base of the alga (as in ''

Laminaria ''Laminaria'' is a genus of brown seaweed in the order Laminariales (kelp), comprising 31 species native to the north Atlantic and northern Pacific Oceans. This economically important genus is characterized by long, leathery laminae and relati ...

''), or it may develop into a large, complex structure running throughout the algal body (as in ''

'' or ''

''). In the most structurally differentiated brown algae (such as ''

Fucus ''Fucus'' is a genus of brown algae found in the intertidal zones of rocky seashores almost throughout the world. Description and life cycle The thallus is perennial with an irregular or disc-shaped holdfast or with haptera. The erect portion o ...

''), the tissues within the stipe are divided into three distinct layers or regions. These regions include a central pith, a surrounding cortex, and an outer epidermis, each of which has an analog in the stem of a vascular plant. In some brown algae, the pith region includes a core of elongated cells that resemble the

of vascular plants both in structure and function. In others (such as '' Nereocystis''), the center of the stipe is hollow and filled with gas that serves to keep that part of the alga buoyant. The stipe may be relatively flexible and elastic in species like '' Macrocystis pyrifera'' that grow in strong currents, or may be more rigid in species like '' Postelsia palmaeformis'' that are exposed to the atmosphere at low tide. Many algae have a flattened portion that may resemble a leaf, and this is termed a ''blade'', ''

lamina Lamina may refer to: Science and technology * Planar lamina, a two-dimensional planar closed surface with mass and density, in mathematics * Laminar flow, (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption betwee ...

'', or ''frond''. The name ''blade'' is most often applied to a single undivided structure, while ''frond'' may be applied to all or most of an algal body that is flattened, but this distinction is not universally applied. The name ''lamina'' refers to that portion of a structurally differentiated alga that is flattened. It may be a single or a divided structure, and may be spread over a substantial portion of the alga. In rockweeds, for example, the lamina is a broad wing of tissue that runs continuously along both sides of a branched ''midrib''. The midrib and lamina together constitute almost all of a rockweed, so that the lamina is spread throughout the alga rather than existing as a localized portion of it. Bladder Wrack (Fucus vesiculosus) - geograph

Bladder Wrack (Fucus vesiculosus) - geograph

In some brown algae, there is a single lamina or blade, while in others there may be many separate blades. Even in those species that initially produce a single blade, the structure may tear with rough currents or as part of maturation to form additional blades. These blades may be attached directly to the stipe, to a holdfast with no stipe present, or there may be an air bladder between the stipe and blade. The surface of the lamina or blade may be smooth or wrinkled; its tissues may be thin and flexible or thick and leathery. In species like ''

Egregia menziesii ''Egregia menziesii'' is a species of kelp known commonly as feather boa kelp. It is the only species in the monotypic genus ''Egregia''. It is native to the coastline of western North America from Alaska to Baja California, where it is a com ...

'', this characteristic may change depending upon the turbulence of the waters in which it grows. In other species, the surface of the blade is coated with slime to discourage the attachment of epiphytes or to deter

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

s. Blades are also often the parts of the alga that bear the reproductive structures. Gas-filled floats called ''

pneumatocyst In phycology, a pneumatocyst is a floating structure that contains gas found on brown seaweed. A seaweed's thallus may have more than one. They provide buoyancy to lift the blades toward the surface, allowing them to receive more sunlight for p ...

s'' provide

buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the ...

in many

s and members of the

. These bladder-like structures occur in or near the ''lamina'', so that it is held nearer the water surface and thus receives more light for photosynthesis. Pneumatocysts are most often spherical or ellipsoidal, but can vary in shape among different species. Species such as '' Nereocystis luetkeana'' and '' Pelagophycus porra'' bear a single large pneumatocyst between the top of the stipe and the base of the blades. In contrast, the giant kelp ''Macrocystis pyrifera'' bears many blades along its stipe, with a pneumatocyst at the base of each blade where it attaches to the main stipe. Species of ''

'' also bear many blades and pneumatocysts, but both kinds of structures are attached separately to the stipe by short stalks. In species of ''

'', the pneumatocysts develop within the lamina itself, either as discrete spherical bladders or as elongated gas-filled regions that take the outline of the lamina in which they develop.

Growth

The brown algae include the largest and fastest growing of seaweeds. Fronds of ''

'' may grow as much as per day, and the stipes can grow in a single day. Growth in most brown algae occurs at the tips of structures as a result of divisions in a single ''apical cell'' or in a row of such cells. They are single cellular organisms. As this apical cell divides, the new cells that it produces develop into all the tissues of the alga. Branchings and other lateral structures appear when the apical cell divides to produce two new apical cells. However, a few groups (such as ''

'') grow by a diffuse, unlocalized production of new cells that can occur anywhere on the thallus.

Tissue organization

The simplest browns are filamentous—that is, their cells are elongate and have septa cutting across their width. They branch by getting wider at their tip, and then dividing the widening. These filaments may be haplostichous or polystichous, multiaxial or monoaxial forming or not
pseudoparenchyma
Besides fronds, there are the large in size parenchymatic kelps with three-dimensional development and growth and different tissues ( meristoderm,

cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

and

medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of t ...

) which could be consider the trees of the sea. There are also the

and

Dictyotales Dictyotales is a large order in the brown algae (class Phaeophyceae). Members of this order generally prefer warmer waters than other brown algae. One genus in this order is calcareous, '' Padina'', the only calcareous member of this phylum. ' ...

smaller than kelps but still parenchymatic with the same kind of distinct tissues. The cell wall consists of two layers; the inner layer bears the strength, and consists of

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...

; the outer wall layer is mainly

algin Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Its colour ...

, and is gummy when wet but becomes hard and brittle when it dries out. Specifically, the brown algal cell wall consists of several components with alginates and sulphated fucan being its main ingredients, up to 40% each of them. Cellulose, a major component from most plant cell walls, is present in a very small percentage, up to 8%. Cellulose and alginate biosynthesis pathways seem to have been acquired from other organisms through endosymbiotic and horizontal gene transfer respectively, while the sulphated polysaccharides are of ancestral origin. Specifically, the cellulose synthases seem to come from the red alga endosymbiont of the photosynthetic stramenopiles ancestor, and the ancestor of brown algae acquired the key enzymes for alginates biosynthesis from an

actinobacterium The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to so ...

. The presence and fine control of alginate structure in combination with the cellulose which existed before it, gave potentially the brown algae the ability to develop complex structurally multicellular organisms like the kelps.

Evolutionary history

Genetic and ultrastructural evidence place the Phaeophyceae among the

heterokont Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...

s (Stramenopiles), a large assemblage of organisms that includes both photosynthetic members with plastids (such as the

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s) as well as non-photosynthetic groups (such as the

slime net The Labyrinthulomycetes (ICBN) or Labyrinthulea (ICZN) are a class of protists that produce a network of filaments or tubes, which serve as tracks for the cells to glide along and absorb nutrients for them. The two main groups are the labyrint ...

s and

water mold Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the result ...

s). Although some heterokont relatives of the brown algae lack plastids in their cells, scientists believe this is a result of evolutionary loss of that organelle in those groups rather than independent acquisition by the several photosynthetic members. Thus, all heterokonts are believed to descend from a single

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

ancestor that became photosynthetic when it acquired plastids through

endosymbiosis An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...

of another unicellular eukaryote. The closest relatives of the brown algae include unicellular and filamentous species, but no unicellular species of brown algae are known. However, most scientists assume that the Phaeophyceae evolved from unicellular ancestors. DNA sequence comparison also suggests that the brown algae evolved from the filamentous

Phaeothamniophyceae Phaeothamniophycidae is a sub class of heterokont algae. It contains two orders, Phaeothamniales and Pleurochloridellales, and consists of species separated from Chrysophyceae The Chrysophyceae, usually called chrysophytes, chrysomonads, go ...

Xanthophyceae Yellow-green algae or the Xanthophyceae (xanthophytes) are an important group of heterokont algae. Most live in fresh water, but some are found in marine and soil habitats. They vary from single-celled flagellates to simple colonial and filamen ...

, or the

Chrysophyceae The Chrysophyceae, usually called chrysophytes, chrysomonads, golden-brown algae or golden algae are a large group of algae, found mostly in freshwater. Golden algae is also commonly used to refer to a single species, '' Prymnesium parvum'', whic ...

between 150 and 200 million years ago. In many ways, the evolution of the brown algae parallels that of the

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

and red algae, as all three groups possess complex multicellular species with an alternation of generations. Analysis of 5S

rRNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosoma ...

sequences reveals much smaller evolutionary distances among genera of the brown algae than among genera of red or green algae, which suggests that the brown algae have diversified much more recently than the other two groups.

Fossils

The occurrence of Phaeophyceae as

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s is rare due to their generally soft-bodied nature, and scientists continue to debate the identification of some finds. Part of the problem with identification lies in the

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

of morphologies between many brown and red algae. Most fossils of soft-tissue algae preserve only a flattened outline, without the microscopic features that permit the major groups of multicellular algae to be reliably distinguished. Among the brown algae, only species of the genus '' Padina'' deposit significant quantities of minerals in or around their cell walls. Other algal groups, such as the red algae and

, have a number of

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an ad ...

members. Because of this, they are more likely to leave evidence in the fossil record than the soft bodies of most brown algae and more often can be precisely classified. Fossils comparable in morphology to brown algae are known from strata as old as the Upper

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

, but the taxonomic affinity of these impression fossils is far from certain. Claims that earlier Ediacaran fossils are brown algae have since been dismissed. While many

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

aceous fossils have been described from the Precambrian, they are typically preserved as flattened outlines or fragments measuring only millimeters long. Because these fossils lack features diagnostic for identification at even the highest level, they are assigned to fossil

form taxa Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of s ...

according to their shape and other gross morphological features. A number of

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

fossils termed ''fucoids'', from their resemblance in outline to species in the genus ''

'', have proven to be inorganic rather than true fossils. The Devonian megafossil ''

Prototaxites ''Prototaxites'' is a genus of terrestrial fossil fungi dating from the Middle Ordovician until the Late Devonian periods, approximately . ''Prototaxites'' formed small to large trunk-like structures up to wide, reaching in length, made up of ...

'', which consists of masses of filaments grouped into trunk-like axes, has been considered a possible brown alga. However, modern research favors reinterpretation of this fossil as a terrestrial

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

or fungal-like organism. Likewise, the fossil ''

Protosalvinia ''Protosalvinia'' is a prehistoric plant found commonly in shale from shoreline habitats of the Upper Devonian period. The name ''Protosalvinia'' is a misnomer. The name literally means ''early Salvinia'', and was given in the erroneous belie ...

'' was once considered a possible brown alga, but is now thought to be an early

land plant The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sist ...

. A number of

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

fossils have been tentatively classified with the brown algae, although most have also been compared to known red algae species. '' Phascolophyllaphycus'' possesses numerous elongate, inflated blades attached to a stipe. It is the most abundant of algal fossils found in a collection made from

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

strata in

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...

. Each hollow blade bears up to eight

s at its base, and the stipes appear to have been hollow and inflated as well. This combination of characteristics is similar to certain modern genera in the order

(kelps). Several fossils of '' Drydenia'' and a single specimen of '' Hungerfordia'' from the Upper Devonian of New York have also been compared to both brown and red algae. Fossils of ''Drydenia'' consist of an elliptical blade attached to a branching filamentous holdfast, not unlike some species of ''

'', ''

Porphyra ''Porphyra'' is a genus of coldwater seaweeds that grow in cold, shallow seawater. More specifically, it belongs to red algae phylum of laver species (from which comes laverbread), comprising approximately 70 species.Brodie, J.A. and Irvine, ...

'', or '' Gigartina''. The single known specimen of ''Hungerfordia'' branches dichotomously into lobes and resembles genera like '' Chondrus'' and ''

'' or ''

Dictyota ''Dictyota'' is a genus of brown seaweed in the family Dictyotaceae. Species are predominantly found in tropical and subtropical seas, and are known to contain numerous chemicals (diterpenes) which have potential medicinal value. As at the end of ...

''. The earliest known fossils that can be assigned reliably to the Phaeophyceae come from

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

diatomite Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 μm to le ...

deposits of the

Monterey Formation The Monterey Formation is an extensive Miocene oil-rich geological sedimentary formation in California, with outcrops of the formation in parts of the California Coast Ranges, Peninsular Ranges, and on some of California's off-shore islan ...

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

. Several soft-bodied brown macroalgae, such as '' Julescraneia'', have been found.

Classification

Phylogeny

Based on the work of Silberfeld, Rousseau & de Reviers 2014.

Taxonomy

This is a list of the orders in the class Phaeophyceae: * Class Phaeophyceae Hansgirg 1886 ucophyceae; Melanophycidae Rabenhorst 1863 stat. nov. Cavalier-Smith 2006** Subclass Discosporangiophycidae Silberfeld, Rousseau & Reviers 2014 *** Order Discosporangiales Schmidt 1937 emend. Kawai et al. 2007 **** Family Choristocarpaceae Kjellman 1891 **** Family Discosporangiaceae Schmidt 1937 ** Subclass Ishigeophycidae Silberfeld, Rousseau & Reviers 2014 *** Order

Ishigeales Ishigeales is an order of brown algae. It includes two families, Ishigeaceae ''Ishige'' is a genus of brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many se ...

Cho & Boo 2004 **** Family Ishigeaceae Okamura 1935 **** Family Petrodermataceae Silberfeld, Rousseau & Reviers 2014 ** Subclass Dictyotophycidae Silberfeld, Rousseau & Reviers 2014 *** Order

Bory de Saint-Vincent 1828 ''ex'' Phillips ''et al.'' **** Family

Dictyotaceae Dictyotaceae is large family of brown algae (class Phaeophyceae). Members of this family generally prefer warmer waters than other brown algae. ''Lobophora variegata'' (= '' Pocockiella varieagata'') often presents a beautiful blue iridescence ...

Lamouroux ex Dumortier 1822 coresbyellaceae Womersley 1987; Dictyopsidaceae*** Order

Onslowiales Onslowiaceae is the only family in order Onslowiales in the brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Nor ...

Draisma & Prud’homme van Reine 2008 **** Family

Onslowiaceae Onslowiaceae is the only family in order Onslowiales in the brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Nor ...

Draisma & Prud’homme van Reine 2001 *** Order

Sphacelariales Sphacelariales is an order of brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae ...

Migula 1909 **** Family Cladostephaceae Oltmanns 1922 **** Family Lithodermataceae Hauck 1883 **** Family Phaeostrophiaceae Kawai et al. 2005 **** Family

Sphacelariaceae Sphacelariaceae is a family of algae belonging to the order Sphacelariales. Genera: * '' Battersia'' Reinke ex Batters, 1890 * '' Chaetopteris'' Kützing, 1843 * '' Herpodiscus'' G.R.South, 1974 * '' Onslowia'' * '' Sphacelaria'' Lyngbye, 1818 ...

Decaisne 1842 **** Family Sphacelodermaceae Draisma, Prud’homme & Kawai 2010 **** Family Stypocaulaceae Oltmanns 1922 *** Order Syringodermatales Henry 1984 **** Family Syringodermataceae Henry 1984 ** Subclass

Fucophycidae Fucophycidae is a subclass of Phaeophyceae (brown algae) which contains the most complex and evolved orders of Chromista algae. The members of this subclass have stalks with several morphological forms and distinct structures, characterized by ...

Cavalier-Smith 1986 *** Order Ascoseirales Petrov1964 emend. Moe & Henry 1982 **** Family

Ascoseiraceae ''Ascoseira'' is a monotypic genus of seaweed in the brown algae (class Phaeophyceae). The single and type species, ''Ascoseira mirabilis'' Skottsberg, is a large parenchymatous macroalgae, and is Endemism, endemic to the Southern Ocean, Antarct ...

Skottsberg 1907 *** Order Asterocladales T.Silberfeld et al. 2011 **** Family Asterocladaceae Silberfeld et al. 2011 *** Order

Desmarestiales Desmarestiales is an order in the brown algae (Phaeophyceae). Members of this order have terete or ligulate (flat) pinnately branched thalli attached by discoid holdfasts. They have a sporphytic thallus usually aggregated to form a pseudo-par ...

Setchell & Gardner 1925 **** Family Arthrocladiaceae Chauvin 1842 **** Family

Desmarestiaceae Desmarestiaceae is a family of brown algae, one of two families in the order Desmarestiales.Guiry, M. D. & G. M. Guiry. 2013Desmarestiales.AlgaeBase. National University of Ireland, Galway. Accessed 04 June 2013. The family gets its name from th ...

(Thuret) Kjellman 1880 *** Order

Ectocarpales Ectocarpales is a very large order in the brown algae (class Phaeophyceae). The order includes families with pseudoparenchymatous (Splachnidiaceae) or true parenchymatous ( Scytosiphonaceae) tissue. Pseudoparenchymatous refers to a filamento ...

Bessey 1907 emend. Rousseau & Reviers 1999a hordariales Setchell & Gardner 1925; Dictyosiphonales Setchell & Gardner 1925; Scytosiphonales Feldmann 1949**** Family

Acinetosporaceae Acinetosporaceae is a family of brown algae in the order Ectocarpales Ectocarpales is a very large order in the brown algae (class Phaeophyceae). The order includes families with pseudoparenchymatous (Splachnidiaceae) or true parenchymatou ...

Hamel ex Feldmann 1937 ylaiellaceae; Pilayellaceae**** Family Adenocystaceae Rousseau et al. 2000 emend. Silberfeld et al. 2011 hordariopsidaceae**** Family

Chordariaceae Chordariaceae is a family of brown algae. Members of this family are may be filamentous, crustose with fused cells at the base, or they may be terete and differentiated into a central medulla and an outer photosynthetic cortex. They have a spo ...

Greville 1830 emend. Peters & Ramírez 2001 yrionemataceae**** Family

Ectocarpaceae Ectocarpaceae is a family of brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae ar ...

Agardh 1828 emend. Silberfeld et al. 2011 **** Family Petrospongiaceae Racault et al. 2009 **** Family

Scytosiphonaceae Scytosiphonaceae is a family of brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae ...

Ardissone & Straforello 1877 hnoosporaceae Setchell & Gardner 1925*** Order

Bory de Saint-Vincent 1827 otheiales Womersley 1987; Durvillaeales Petrov 1965**** Family Bifurcariopsidaceae Cho et al. 2006 **** Family

Durvillaeaceae ''Durvillaea'' is a genus of large brown algae in the monotypic family Durvillaeaceae. All members of the genus are found in the southern hemisphere, including Australia, New Zealand, South America, and various subantarctic islands. ''Durvillae ...

(Oltmanns) De Toni 1891 **** Family

Fucaceae The Fucaceae are a family of brown algae, containing six genera: *''Ascophyllum'' Stackhouse – one species *''Fucus'' L. – 15 species *'' Hesperophycus'' Setchell & Gardner – one species *'' Pelvetia'' Decne. & Thur. – one species *'' Pel ...

Adanson 1763 **** Family

Himanthaliaceae ''Himanthalia'' is a genus of brown algae. It is the only genus in the family Himanthaliaceae in the order Fucales. It includes two species: '' Himanthalia durvillei'' and '' Himanthalia elongata''. References {{Taxonbar, from1=Q18364313, f ...

(Kjellman) De Toni 1891 **** Family

Hormosiraceae ''Hormosira banksii'', also known as Neptune's necklace, Neptune's pearls, sea grapes, or bubbleweed) is a species of seaweed (brown algae, Fucales) native to Australia and New Zealand. The genus ''Hormosira'' is monotypic. Distribution ''Horm ...

Fritsch 1945 **** Family

Notheiaceae The Notheiaceae is a family of brown algae. References Fucales Brown algae families {{Phaeophyceae-stub ...

Schmidt 1938 **** Family

Sargassaceae Sargassaceae is a family of brown algae in the order Fucales The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly ac ...

Kützing 1843 ystoseiraceae De Toni 1891**** Family

Seirococcaceae The Seirococcaceae are a family of brown alga Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown ...

Nizamuddin 1987 **** Family Xiphophoraceae Cho et al. 2006 *** Order

Migula 1909 haeosiphoniellales Silberfeld, Rousseau & Reviers 2014 ord. nov. prop.**** Family Agaraceae Postels & Ruprecht 1840 ostariaceae**** Family Akkesiphycaceae Kawai & Sasaki 2000 **** Family

Alariaceae Alariaceae are a family of brown algae in the order Laminariales. Genera * '' Alaria'' * '' Eualaria'' * '' Lessoniopsis'' * '' Pleurophycus'' * '' Pterygophora'' * '' Undaria'' (e.g. wakame) * '' Undariella'' Distribution The distribution of ...

Setchell & Gardner 1925 **** Family Aureophycaceae Kawai & Ridgway 2013 **** Family

Chordaceae ''Chorda'' is a genus of thalloid brown algae including two species. It is the only genus in the family Chordaceae. Its members are known by a number of common names including: mermaid's fishing line, tsurumo, ruálach, doruithe briain, sea laces ...

Dumortier 1822 **** Family

Laminariaceae Laminariaceae is a family of brown algal seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and '' Chlor ...

Bory de Saint-Vincent 1827 rthrothamnaceae Petrov 1974**** Family

Lessoniaceae Lessoniaceae are a family of kelp. Species of this family have transition zone with intercalary meristem subdivided so that there are a number of secondary stipes in addition to the primary stipe. Genera and species *'' Ecklonia'' **'' Ecklonia ...

Setchell & Gardner 1925 **** Family

Pseudochordaceae ''Pseudochorda'' is a genus of thalloid brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Bro ...

Kawai & Kurogi 1985 *** Order Nemodermatales Parente et al. 2008 **** Family Nemodermataceae Kuckuck ex Feldmann 1937 *** Order Phaeosiphoniellales Silberfeld, Rousseau & Reviers 2014 **** Family Phaeosiphoniellaceae Phillips et al. 2008 *** Order

Ralfsiales Ralfsiales is an order of crustose brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown a ...

Nakamura ex Lim & Kawai 2007 **** Family Mesosporaceae Tanaka & Chihara 1982 **** Family Neoralfsiaceae Lim & Kawai 2007 **** Family

Ralfsiaceae Ralfsiaceae is a family of brown algae in the order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein t ...

Farlow 1881 [Heterochordariaceae Setchell & Gardner 1925] *** Order Scytothamnales Peters & Clayton 1998 emend. Silberfeld et al. 2011 **** Family Asteronemataceae Silberfeld et al. 2011 **** Family Bachelotiaceae Silberfeld et al. 2011 **** Family Splachnidiaceae Mitchell & Whitting 1892 [Scytothamnaceae Womersley 1987] *** Order Sporochnales Camille Sauvageau, Sauvageau 1926 **** Family Sporochnaceae Greville 1830 *** Order Tilopteridales Bessey 1907 emend. Phillips et al. 2008 [Cutleriales Bessey 1907] **** Family Cutleriaceae Griffith & Henfrey 1856 **** Family Halosiphonaceae Kawai & Sasaki 2000 **** Family Phyllariaceae Tilden 1935 **** Family Stschapoviaceae Kawai 2004 **** Family Tilopteridaceae Kjellman 1890 Laminaria Life Cycle

Life cycle

Most brown algae, with the exception of the

, perform sexual reproduction through sporic meiosis. Between generations, the algae go through separate sporophyte (diploid) and gametophyte (haploid) phases. The sporophyte stage is often the more visible of the two, though some species of brown algae have similar diploid and haploid phases. Free floating forms of brown algae often do not undergo sexual reproduction until they attach themselves to substrate. The haploid generation consists of male and female gametophytes. The fertilization of egg cells varies between species of brown algae, and may be Isogamy, isogamous, Oogamy, oogamous, or Anisogamy, anisogamous. Fertilization may take place in the water with eggs and motile sperm, or within the oogonium itself. Certain species of brown algae can also perform asexual reproduction through the production of motile diploid zoospores. These zoospores form in plurilocular sporangium, and can mature into the sporophyte phase immediately. In a representative species ''

'', there is a conspicuous diploid generation and smaller haploid generations. Meiosis takes place within several Locule, unilocular sporangium along the algae's blade, each one forming either haploid male or female zoospores. The spores are then released from the sporangia and grow to form male and female gametophytes. The female gametophyte produces an egg in the oogonium, and the male gametophyte releases motile sperm that fertilize the egg. The fertilized zygote then grows into the mature diploid sporophyte. In the order

, sexual reproduction is oogamous, and the mature diploid is the only form for each generation. Gametes are formed in specialized conceptacles that occur scattered on both surfaces of the receptacle, the outer portion of the blades of the parent plant. Egg cells and motile sperm are released from separate sacs within the conceptacles of the parent algae, combining in the water to complete fertilization. The fertilized zygote settles onto a surface and then differentiates into a leafy

and a finger-like holdfast. Light regulates differentiation of the zygote into blade and holdfast. Saccharina latissima NOAA

Ecology

Brown algae have adapted to a wide variety of marine ecological niches including the tidal splash zone, rock pools, the whole intertidal zone and relatively deep near shore waters. They are an important constituent of some brackish water ecosystems, and have colonized freshwater on a maximum of six known occasions. A large number of Phaeophyceae are intertidal or upper littoral, and they are predominantly cool and cold water organisms that benefit from nutrients in up welling cold water currents and inflows from land; ''

'' being a prominent exception to this generalisation. Brown algae growing in brackish waters are almost solely asexual.

Chemistry

Brown algae have a value in the range of , in contrast with red algae and greens. This reflects their different metabolic pathways. They have cellulose walls with alginic acid and also contain the polysaccharide fucoidan in the amorphous sections of their cell walls. A few species (of ''Padina'') calcify with aragonite needles. In addition to alginates, fucoidan and cellulose, the carbohydrate composition of brown algae consist of mannitol, laminarin and glucan. The photosynthetic system of brown algae is made of a P700 complex containing chlorophyll a. Their plastids also contain chlorophyll c and carotenoids (the most widespread of those being

). Brown algae produce a specific type of tannin called phlorotannins in higher amounts than red algae do.

Importance and uses

Brown algae include a number of edible seaweeds. All brown algae contain alginic acid (alginate) in their cell walls, which is extracted commercially and used as an industrial thickening agent in food and for other uses. One of these products is used in lithium-ion batteries. Alginic acid is used as a stable component of a battery anode. This polysaccharide is a major component of brown algae, and is not found in land plants. Alginic acid can also be used in aquaculture. For example, alginic acid enhances the immune system of rainbow trout. Younger fish are more likely to survive when given a diet with alginic acid. Brown algae including

beds also fix a significant portion of the earth's carbon dioxide yearly through photosynthesis. Additionally, they can store a great amount of carbon dioxide which can help us in the fight against climate change. Sargachromanol, Sargachromanol G, an extract of Sargassum siliquastrum, has been shown to have anti-inflammatory effects.

Edible Brown Algae

Kelp (Laminariales)

* Arame (''Eisenia bicyclis'') * Badderlocks (''Alaria esculenta'') * Cochayuyo (''Durvillaea antarctica'') * ''Ecklonia cava'' * Kombu (''Saccharina japonica'') * Oarweed (''Laminaria digitata'') * Sea palm '' Postelsia palmaeformis'' * Sea whip (''Nereocystis luetkeana'') * Sugar kelp (''Saccharina latissima'') * Wakame (''Undaria pinnatifida'') * Hiromi (''Undaria undarioides'') * Grapestone (''Mastocarpus papillatus'')

Fucales The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebaseref name="Guiry and Guiry">Guiry, M.D. and ...

* Bladderwrack (''Fucus vesiculosus'') * Channelled wrack (''Pelvetia canaliculata'') * Hijiki or Hiziki (''Sargassum fusiforme'') * Limu Kala (''Sargassum echinocarpum'') * ''

'' ** ''Sargassum cinetum'' ** ''Sargassum vulgare'' ** ''Sargassum swartzii'' ** ''Sargassum myriocysum'' * Spiral wrack (''Fucus spiralis'') * Thongweed (''Himanthalia elongata'')

Ectocarpales Ectocarpales is a very large order in the brown algae (class Phaeophyceae). The order includes families with pseudoparenchymatous (Splachnidiaceae) or true parenchymatous ( Scytosiphonaceae) tissue. Pseudoparenchymatous refers to a filamento ...

* Mozuku (''Cladosiphon okamuranus'')

References

External links

Monterey Bay Flora

University of California Museum of Paleontology
Phaeophyceae
National University of Ireland, Galway {{Authority control Brown algae, Biological oceanography Tithonian first appearances Extant Late Jurassic first appearances

Morphology

Visible structures

Growth

Tissue organization

Evolutionary history

Fossils

Classification

Phylogeny

Taxonomy

Life cycle

Ecology

Chemistry

Importance and uses

Edible Brown Algae

Kelp (Laminariales)

Fucales The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebaseref name="Guiry and Guiry">Guiry, M.D. and ...

Ectocarpales Ectocarpales is a very large order in the brown algae (class Phaeophyceae). The order includes families with pseudoparenchymatous (Splachnidiaceae) or true parenchymatous ( Scytosiphonaceae) tissue. Pseudoparenchymatous refers to a filamento ...

See also

References

External links