Yellow-green algae or the Xanthophyceae (xanthophytes) are an important group of

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 ...

algae. Most live in fresh water, but some are found in marine and soil habitats. They vary from single-celled

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their ...

s to simple colonial and filamentous forms. Xanthophyte

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

s contain the

photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...

pigments chlorophyll ''a'', chlorophyll ''c'',

β-carotene β-Carotene is an organic, strongly coloured red-orange pigment abundant in fungi, plants, and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 40 ...

, and the

carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, and Fungus, fungi. Carotenoids give the characteristic color to pumpki ...

diadinoxanthin Diadinoxanthin is a pigment found in phytoplankton. It has the formula C40H54O3. It gives rise to the xanthophylls diatoxanthin and dinoxanthin. Diadinoxanthin is a plastid pigment. Plastid pigments include chlorophylls a and c, fucoxanthin, hete ...

. Unlike other heterokonts, their chloroplasts do not contain

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 accounts for their lighter colour. Their storage

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...

is chrysolaminarin. Xanthophyte cell walls are produced 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 wall ...

and

hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls.Scheller HV, Ulvskov H ...

. They appear to be the closest relatives of 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 Northern Hemisphere. Brown algae are the major seaweeds of the temperate and po ...

Classifications

The species now placed in the Xanthophyceae were formerly included in the

Chlorophyceae The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, p ...

. In 1899, Lüther created the group Heterokontae for green algae with unequal flagella. Pascher (1914) included the Heterokontae in the Chrysophyta. In 1930, Allorge renamed the group as Xanthophyceae. The monadoid (unicellular flagellates) and also sometimes the amoeboid species have been included by some authors in the

Protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

Protista A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the excl ...

, as order Heterochloridina (e.g., Doflein and Reichenow, 1927-1929), as class Xanthomonadina, with orders Heterochloridea and Rhizochloridea (e.g., Deflandre, 1956), as order Heterochlorida (e.g., Hall, 1953, Honigberg et al., 1964), as order Heteromonadida (e.g., Leedale, 1983), or as subclass Heterochloridia (e.g., Puytorac et al., 1987). These groups are called

ambiregnal protist Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms. To an end-user who only deals with names of species, with some awareness that species ...

s, as names for these have been published under either or both of the ICZN and the ICN.

AlgaeBase (2020)

Xanthophyceae have been divided into the following five orders in some classification systems: * '' Dictyosphaeriopsis'' * '' Groenlandiella'' * '' Halosphaeropsis'' * '' Pelagocystis'' * '' Polyedrium'' * '' Pseudopleurochloris'' * '' Raphidosphaera'' * '' Sphaerochloris'' * ''

Tiresias In Greek mythology, Tiresias (; grc, Τειρεσίας, Teiresías) was a blind prophet of Apollo in Thebes, famous for clairvoyance and for being transformed into a woman for seven years. He was the son of the shepherd Everes and the nymph ...

'' * Order Botrydiales Schaffner 1922 ** Family Botrydiaceae Rabenhorst 1863 *** '' Asterosiphon'' *** '' Botrydium'' *** '' Polychloris'' * Order Mischococcales Fritsch 1927 ** Family Botrydiopsidaceae Hibberd 1980 *** '' Botrydiopsis'' *** '' Excentrochloris'' *** '' Perone'' ** Family Botryochloridaceae Pascher 1938 *** '' Botryochloris'' *** '' Chlorellidiopsis'' *** '' Chlorellidium'' *** '' Ducellieria'' *** '' Heterodesmus'' *** '' Ilsteria'' *** '' Raphidiella'' *** '' Sphaerosorus'' *** '' Tetraktis'' ** Family Centritractaceae Pascher 1937 *** '' Bumilleriopsis'' *** '' Centritractus'' *** '' Pseudotetraëdron'' ** Family Characiopsidaceae Pascher 1938 *** '' Characiopsis'' *** '' Chlorokoryne'' *** '' Chlorothecium'' *** '' Chytridiochloris'' *** '' Dioxys'' *** '' Harpochytrium'' *** '' Hemisphaerella'' *** '' Lutherella'' *** '' Peroniella'' ** Family Chloropediaceae Pascher 1931 *** '' Chloropedia'' ** Family Gloeobotrydaceae Pascher 1937 *** '' Chlorosaccus'' *** '' Asterogloea'' *** '' Dictyosphaeriopsis'' *** '' Gaumiella'' *** '' Gloeobotrys'' *** '' Gloeoskene'' *** '' Gloeosphaeridium'' *** '' Merismogloea'' ** Family Gloeopodiaceae Pascher 1938 *** '' Gloeopodium'' ** Family Mischococcaceae Pascher 1912 *** '' Mischococcus'' ** Family Ophiocytiaceae Lemmermann 1899 *** '' Ophiocytium'' ** Family Pleurochloridaceae Pascher 1937 *** '' Acanthochloris'' *** '' Actinellipsoidion'' *** '' Arachnochloris'' *** '' Aulakochloris'' *** '' Bracchiogonium'' *** '' Chlorallanthus'' *** '' Chlorapion'' *** '' Chlorarkys'' *** '' Chloridella'' *** '' Chlorocloster'' *** '' Chlorogibba'' *** '' Diachros'' *** '' Endochloridion'' *** '' Isthmochloron'' *** '' Keriosphaera'' *** '' Leuvenia'' *** '' Meringosphaera'' *** '' Monallanthus'' *** '' Monodus'' *** '' Nephrodiella'' *** '' Osterhoutia'' *** '' Pleurochloridella'' *** '' Pleurochloris'' *** '' Pleurogaster'' *** '' Polyedriella'' *** '' Polygoniochloris'' *** '' Prismatella'' *** '' Pseudogoniochloris'' *** '' Pseudopolyedriopsis'' *** '' Rhomboidella '' *** '' Schilleriella'' *** '' Skiadosphaera'' *** '' Sklerochlamys'' *** '' Tetraplektron'' *** '' Trachychloron'' ** Family Trypanochloridaceae Geitler ex Pascher 1938 *** '' Trypanochloris'' * Order Rhizochloridales Pascher 1925 *** '' Garciamyxa'' *** '' Herreramyxa'' *** '' Requejomyxa'' ** Family Myxochloridaceae Pascher 1937 *** '' Myxochloris'' ** Family Rhizochloridaceae Pascher 1925 *** '' Aldavemyxa'' *** '' Heterocalycina'' *** '' Rhizochloris'' ** Family Stipitococcaceae Pascher ex Smith 1933 *** '' Rhizolekane'' *** '' Stipitococcus'' *** '' Stipitoporos'' * Order Tribonematales Pascher 1939 ** Family Heterodendraceae Pascher 1939 *** '' Heterodendron'' ** Family Heteropediaceae Hibberd 1982 *** '' Capitulariella'' *** '' Chaetopedia'' *** ''

Heterococcus ''Heterococcus'' is a genus of 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 singl ...

'' *** '' Heteropedia'' *** '' Sphagnoikos'' ** Family Neonemataceae Ettl 1977 *** '' Neonema'' ** Family Tribonemataceae West 1904 *** '' Brachynematella'' *** '' Bumilleria'' *** ''

Tribonema ''Tribonema'' is a genus of filamentous, freshwater yellow-green algae. The holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally ...

'' ** Family Xanthonemataceae Silva 1980 *** ?'' Hormotheca'' *** '' Heterotrichella'' *** '' Xanthonema'' * Order Vaucheriales Nägeli ex Bohlin 1901Christensen, T. 1987. ''Seaweeds of the British Isles.'' Volume 4 Tribophyceae (Xanthophyceae). British Museum (Natural History), London ** Family Vaucheriaceae (Gray) Dumortier 1822 *** '' Pseudodichotomosiphon'' *** ''

Vaucheria ''Vaucheria'' is a genus of Xanthophyceae or yellow-green algae known as water felt. It is one of only two genera in the family Vaucheriaceae. The type species of the genus is '' Vaucheria disperma''. The genus was circumscribed by Augustin Py ...

'' *** '' Vaucheriella''

Lüther (1899)

Classification according to Lüther (1899): * Class Heterokontae ** Order Chloromonadales ** Order Confervales

Pascher (1912)

Classification according to Pascher (1912): * Heterokontae ** Heterochloridales ** Heterocapsales ** Heterococcales ** Heterotrichales ** Heterosiphonales

Fritsch (1935)

Fritsch (1935) recognizes the following orders in the class Xanthophyceae: *Order Heterochloridales ** Suborder Heterochlorineae *** Family Heterochloridaceae (e.g., '' Heterochloris'') ** Suborder Heterocapsineae *** Family Heterocapsaceae (e.g., '' Chlorogloea'') ** Suborder Heterodendrineae *** Family Mischococcaceae (e.g., '' Mischococcus'') ** Suborder Heterorhizidineae *** Family Heterorhizidaceae (e.g., '' Rhizolekane'') *Order Heterococcales ** Family Halosphaeraceae (e.g., ''

Halosphaera ''Halosphaera'' is a genus of green algae in the order Pyramimonadales Pyramimonadales are an order of green algae in the Chlorophyta. The chloroplasts of phototrophic euglenids probably came from endosymbiosis with a member of this order. T ...

'') ** Family Myxochloridaceae (e.g., '' Myxochloris'') ** Family Chlorobotrydaceae(e.g., '' Chlorobotrys'') ** Family Chlorotheciaceae (e.g., '' Chlorothecium'') ** Family Ophiocytiaceae (e.g., '' Ophiocytium'') *Order Heterotrichales ** Family Tribonemataceae (e.g., ''

'') ** Family Heterocloniaceae (e.g., '' Heterodendron'' *Order Heterosiphonales ** Family Botrydiaceae (e.g., '' Botrydium'')

Smith (1938)

In the classification of Smith (1938), there are six orders in the class Xanthophyceae, placed in the division Chrysophyta: *Order Heterochloridales (e.g., '' Chlorochromonas'') *Order Rhizochloridales (e.g., ''

Chlorarachnion The chlorarachniophytes are a small group of exclusively marine algae widely distributed in tropical and temperate waters. They are typically mixotrophic, ingesting bacteria and smaller protists as well as conducting photosynthesis. Normally the ...

'') *Order Heterocapsales (e.g., '' Chlorosaccus'') *Order Heterotrichales (e.g., ''

'') *Order Heterococcales (e.g., '' Botrydiopsis'') *Order Heterosiphonales (e.g., '' Botrydium'')

Pascher (1939)

Pascher (1939) recognizes 6 classes in Heterokontae: *Class Heterochloridineae *Class Rhizochloridineae *Class Hetcrocapsineae *Class Heterococcincae *Class Hetcrotrichineae *Class Heterosiphonineae

Copeland (1956)

Copeland (1956) treated the group as order Vaucheriacea: * Kingdom Protoctista ** Phylum

Phaeophyta 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 are the major seaweeds of the temperate and ...

*** Class

Heterokonta 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 ...

**** Order Vaucheriacea ***** Family Chlorosaccacea ***** Family Mischococcacea ***** Family Chlorotheciacea ***** Family Botryococcacea ***** Family Stipitococcacea ***** Family Chloramoebacea ***** Family Tribonematacea ***** Family Phyllosiphonacea

Ettl (1978), van den Hoek et al. (1995)

In a classification presented by van den Hoek, Mann and Jahns (1995), based on the

level of organization An integrative level, or level of organization, is a set of phenomena emerging from pre-existing phenomena of a lower level. The levels concept is an intellectual framework for structuring reality. It arranges all entities, structures, and processe ...

of the

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 wer ...

, there are seven orders: * Order Chloramoebales (e.g., '' Chloromeson'') - flagellate organisms * Order Rhizochloridales (e.g., '' Rhizochloris, Myxochloris'') - ameboid organisms * Order Heterogloeales (e.g., '' Gloeochloris'') - palmelloid (tetrasporal) organisms * Order Mischococcales (e.g., '' Chloridella, Botrydiopsis, Characiopsis, Ophiocytium'') - coccoid organisms * Order Tribonematales (e.g., ''

, Heterodendron'') - filamentous organization * Order Botrydiales (e.g., '' Botrydium'') - siphonous organization; sexual reproduction

isogamous Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as male or fe ...

or anisogamous * Order Vaucheriales (e.g., ''

'') - siphonous organization; sexual reproduction oogamous These are the same orders of the classification of Ettl (1978), an updated version of the classic work by Pascher (1939).

Ultrastructural Ultrastructure (or ultra-structure) is the architecture of cells and biomaterials that is visible at higher magnifications than found on a standard optical light microscope. This traditionally meant the resolution and magnification range of a co ...

and molecular studies shows that the Mischococcales might be paraphyletic, and the Tribonematales and Botrydiales polyphyletic, and suggests two orders at most be used until the relationships within the division are sorted.

Maistro et al. (2009)

Informal groups, according to Maistro et al. (2009): * Botrydiopsalean clade * Chlorellidialean clade * Tribonematalean clade * Vaucherialean clade Unicellular flagellates, amoeboid and palmelloid taxa were not included in this study.

Adl et al. (2005, 2012)

According to Adl et al. (2005, 2012): * Tribonematales (genera ''Botrydium, Bumilleriopsis, Characiopsis, Chloromeson, Heterococcus, Ophiocytium, Sphaerosorus, Tribonema, Xanthonema'') * Vaucheriales (genus ''Vaucheria'') File:Stipitococcus capense.svg, ''Stipitococcus capense'' (Rhizochloridales) File:British fresh-water algae, exclusive of Desmidieae and Diatomaceae (1882-1884) (20231360259).jpg, ''Ophiocytium arbusculum'' (Mischococcales), formerly ''Sciadium arbuscula'' File:Alger, Botydium granulatum, Nordisk familjebok.png, ''Botrydium granulatum'' (Botrydiales) File:Vaucheria sp thallus 01.jpg, ''Vaucheria'' sp. (Vaucheriales), thallus File:Vaucheria sp sexial reproductive organ01.jpg, ''Vaucheria'' sp., sexual reproductive organs File:British fresh-water algae, exclusive of Desmidieae and Diatomaceae (1882-1884) (19795451234).jpg, ''Vaucheria'' sp. File:Album général des Cryptogames, Pl. 21.jpg, Other genera

References

{{Taxonbar, from=Q745912