Classification of Algae - BioQuestOnline

F.E. Fritsch (1935) provided the first extensive classification of algae and categorized them into 11 classes viz, Chlorophyceae, Xanthophyceae, Chrysophyceae, Bacillariophyceae, Cryptophyceae, Dinophyceae Chloromonadineae, Euglenineae, Phaeophyceae, Rhodophyceae and Myxophyceae.

Long before Fritsch, Linnaeus in 1753 categorized algae under class cryptogamia along with cryptogams, mosses and fungi.

Pascher (1914-1935), classified algae into 8 divisions and 14 classes based on phylogeny and inter-relationship of various groups.

Fig: Classification of Algae by Pascher (1914-1935)

Table of Contents

Classification of Algae (F.E. Fritsch,1935) With Common Examples

Fritsch categorized algae into 49 distinct orders under 11 classes, in his book ” The Structure and Reproduction of the Algae”.

Fig: Classification of Algae by Fritsch (1935)

Fritsch system of classification of algae is basically focused on pigmentation, flagella types, assimilatory products, thallus organization, and methods of reproduction.

Chlorophyceae
Xanthophyceae
Chrysophyceae
Bacillariophyceae
Cryptophyceae
Dinophyceae
Chloromonadineae
Euglenineae
Phaeophyceae
Rhodophyceae
Myxophyceae

SN	CLASS		ORDERS	COMMON EXAMPLES
1.	Chlorophyceae
		1.	Volvocales	Volvox
		2.	Chlorococcales	Chlorella
		3.	Ulotrichales	Ulothrix
		4.	Cladophorales	Cladophora
		5.	Chaetophorales	Fritschiella
		6.	Oedogoniales	Oedogonium
		7.	Conjugales	Zygnema
		8.	Siphonales	Vaucheria
		9.	Charales	Chara
2.	Xanthophyceae
		1.	Heterochloridales	Heterochloris
		2.	Heterococcales	Myxochloris
		3.	Heterotrichales	Tribonema
		4.	Heterosiphonales	Botrydium
3.	Chrysophyceae
		1.	Chrysomonadales	Chrysodendron
		2.	Chrysosphaerales	Chrysosphaera
		3.	Chrysotrichales	Chrysoclonium
4.	Bacillariophyceae
		1.	Centrales	Cyclotella
		2.	Pennales	Grammatophora
5.	Cryptophyceae
		1.	Crptomonadales	Cryptomonas
		2.	Cryptococcales	Tetragonidium
6.	Dinophyceae
		1.	Desmomonadales	Desmocapsa
		2.	Thecatales	Prorocentrum
		3.	Dinophysiales	Dinophysis
		4.	Dinoflagellates	Elastodinium
		5.	Dinococcales	Dinastridium
		6.	Dinotrichales	Dinothrix
7.	Chloromonadineae
		1.	Chloromonadales	Trentonia
8.	Euglenineae
9.	Phaeophyceae
		1.	Ectocarpales	Ectocarpus
		2.	Tilopteridales	Tilopteris
		3.	Cutleriales	Cutleria
		4.	Sporochnales	Sporochnus
		5.	Desmarestiales	Desmarestia
		6.	Laminariales	Laminaria
		7.	Sphacelariales	Sphacelaria
		8.	Dictyotales	Dictyota
		9.	Fucales	Fucus
10.	Rhodophyceae
		1.	Bangiales	Bangia
		2.	Nemalionales	Batrachospermum
		3.	Gelidiales	Gelidium
		4.	Cryptonemiales	Corallina
		5.	Gigartinales	Gigartina
		6.	Rhodymeniales	Rhodymenia
		7.	Ceramiales	Polysiphonia
11.	Myxophyceae
		1.	Chroococcales	Microcystis
		2.	Chamaesiphonales	Chamesiphon
		3.	Pleurocapsales	Pleurocapsa
		5.	Nostocales	Nostoc
		6.	Stigonematales	Stigonema

Table: Classification of Algae (F. E. Fritsch, 1935)

General Characteristics of Chlorophyceae (Green Algae)

Classification of Algae, Cladophora_prolifera — Fig: *Cladophora_prolifera* [Image by Roth, A.W. Biodiversity Heritage Library, From Wikimedia/Public Domain]

The primary pigments are essentially the same as those found in higher plants, including chlorophyll a and b, carotenoids, and xanthophylls.
Chloroplasts typically contain pyrenoids.
Starch serves as the food reserve and often accumulates around the pyrenoids.
The cell wall is made of cellulose, and the cells are typically eukaryotic.
If flagella are present, they are of equal length and usually positioned at the anterior end.
Reproduction occurs through vegetative, asexual, and sexual (isogamous, anisogamous, and oogamous) methods.

Table: Classification of Algae (Chlorophyceae) With Common Examples

General Characteristics of Xanthophyceae (Yellow-Green Algae)

The primary pigments are chlorophyll a and e, β carotene, and xanthophylls.
Plastids lack pyrenoids. Oil serves as the reserve food material.
The cell wall is primarily composed of pectic substances with a small amount of cellulose.
The cell is a typical eukaryote with two unequal flagella inserted at the anterior end.
The shorter flagellum is of the whiplash type, while the longer one is of the tinsel type.
Reproduction occurs through vegetative, asexual, and isogamous sexual methods.

Table: Classification of Algae (Xanthophyceae) With Common Examples

General Characteristics of Chrysophyceae

Phycochrysin is the predominant pigment, giving these algae their brown or orange color.
The chromatophores contain naked pyrenoid-like bodies.
Chrysolaminarin and leucosin serve as the food reserves.
The cell wall is calcified and lacks cellulose.
The motile cells have two unequal flagella inserted at the anterior end.
Sexual reproduction is very rare, but when it occurs, it is of the isogamous type.

Table: Classification of Algae (Chrysophyceae) With Common Examples

General Characteristics of Bacillariophyceae (Golden-Brown Algae)

This class is characterized by the dominance of golden-brown pigments such as fucoxanthin, diatoxanthin, and diadinoxanthin.
The chromatophores contain pyrenoids, and the photosynthetic products are fat and volutin.
The cell wall is pectic, silicified, and often intricately ornamented.
The cell wall consists of two halves that are either radially or bilaterally symmetrical.
The motile cells usually have a single flagellum.
Sexual reproduction occurs through fusion and the formation of gametes or auxospores.

Table: Classification of Algae (Bacillariophyceae) With Common Examples

General Characteristics of Cryptophyceae

The primary pigment is xanthophyll, giving these algae their brown or red color.
Pyrenoid-like bodies are present, but they are often separate from the chromatophores.
The photosynthetic products are starch or oil.
The motile cells are dorsiventral, with two unequal flagella inserted at the anterior end.
A complex vacuolar system exists within the cell.
Sexual reproduction is rare, and when it occurs, it is of the isogamous type.

Table: Classification of Algae (Cryptophyceae) With Common Examples

General Characteristics of Dinophyceae

These algae possess numerous discoid chromatophores.
Xanthophyll is the primary pigment, giving them a brown or red color.
Starch and fat serve as the food reserves.
The cell wall is composed of cellulose.
Most cells in this class are motile unicells with two flagella.
Many species are colorless saprophytes that exhibit a holozoic mode of nutrition.
Sexual reproduction is rare, and when it occurs, it is isogamous.

Table: Classification of Algae (Dinophyceae) With Common Examples

General Characteristics of Chloromonadineae

Members of this class possess numerous discoid chromatophores, giving them a bright green tint due to the abundance of xanthophyll.
Pyrenoids are absent, and the reserve food consists of fat and oil.
The motile forms have two nearly equal flagella.
Sexual reproduction is absent.
Reproduction occurs through longitudinal cell division.

Table: Classification of Algae (Chloromonadineae) With Common Examples

General Characteristics of Euglenophyceae

These are highly specialized unicellular green flagellates.
The cells typically contain many chromatophores.
Some forms have pyrenoid-like bodies.
The primary pigment is chlorophyll, and the product of photosynthesis is the polysaccharide paramylon.
Most members have one or two flagella originating from the base of a canal-like invagination at the anterior end.
These algae possess a complex vacuolar system.
Reproduction occurs through cell division.
Sexual reproduction is present only in a few forms and is of the isogamous type.

General Characteristics of Phaeophyceae (Brown algae)

Classification of Algae, Fucus_serratus — Fig: *Fucus_serratus* [Image by Alguier des frères Crouan, From WikiMedia /Public Domain]

Structurally, these are the most complex algae.
They range from simple filaments to massive plant bodies.
Their pigments include chlorophyll a and c, and β-carotene; the chromatophores also contain fucoxanthin along with other pigments.
Reserve food is stored as laminarin (a polysaccharide) and mannitol (a form of alcohol).
The cell wall is primarily composed of cellulose with alginic and fucinic acids.
The motile reproductive cells have two lateral or sub-apical flagella, one directed forward and the other backward.
Sexual reproduction varies from isogamy to oogamy.

Table: Classification of Algae (Phaeophyceae) With Common Examples

General Characteristics of Rhodophyceae (Red algae)

Most of these algae are marine and feature uniaxial or multiaxial thalli.
They contain pigments such as chlorophyll a and d, α- and β-carotene, and xanthophyll.
Chromatophores also include r-phycoerythrin and r-phycocyanin, which give these algae their red color.
The food reserve is stored as floridean starch (a polysaccharide).
The outer cell wall is pectic, while the inner cell wall is composed of cellulose.
The reproductive cells are non-motile.
Sexual reproduction is of the advanced oogamous type.

Table: Classification of Algae (Rhodophyceae) With Common Examples

General Characteristics of Myxophyceae (Blue Green Algae)

These algae are characterized by having a very rudimentary nucleus and lack well-organized chromatophores, indicating a prokaryotic cell organization.
The primary pigments are chlorophyll a, β-carotene, and c-phycocyanin.
The cell wall is composed of mucopolymer.
The food reserve is cyanophycean starch.
Sexual reproduction is absent, and asexual reproduction occurs through hormogonia or akinetes.