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 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 i ...

s contain the photosynthetic pigments chlorophyll ''a'', chlorophyll ''c'', β-carotene, and the carotenoid diadinoxanthin. Unlike other heterokonts, their chloroplasts do not contain fucoxanthin, which accounts for their lighter colour. Their storage polysaccharide 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 wa ...

and hemicellulose. They appear to be the closest relatives of the brown algae.

Classifications

The species now placed in the Xanthophyceae were formerly included in the Chlorophyceae. In 1899, Lüther created the group Heterokontae for green algae with unequal flagella. Pascher (1914) included the Heterokontae in the

Chrysophyta Chrysophyta or golden algae is a term used to refer to certain heterokonts. It can be used to refer to: * Chrysophyceae (golden algae), Bacillariophyceae (diatoms), and Xanthophyceae (yellow-green algae) together. E.g., Pascher (1914). * Chrysoph ...

. 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 or

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 e ...

, 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'' * Order

Botrydiales Botrydiaceae is a family of yellow-green algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multip ...

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

'' *** '' 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'') ** Family Myxochloridaceae (e.g., '' Myxochloris'') ** Family Chlorobotrydaceae(e.g., ''

Chlorobotrys ''Chlorobotrys'' is a genus of algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct ...

'') ** Family Chlorotheciaceae (e.g., '' Chlorothecium'') ** Family Ophiocytiaceae (e.g., '' Ophiocytium'') *Order Heterotrichales ** Family Tribonemataceae (e.g., '' Tribonema'') ** 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'') *Order Heterocapsales (e.g., '' Chlorosaccus'') *Order Heterotrichales (e.g., '' Tribonema'') *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 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 exclu ...

** 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 **** 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 processes ...

of the thallus, 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., '' Tribonema, Heterococcus, Heterodendron'') - filamentous organization * Order

(e.g., '' Botrydium'') - siphonous organization; sexual reproduction isogamous 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 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