Zygnematophyceae (or Conjugatophyceae) is a class of

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 ...

in the paraphylum streptophyte algae, also referred to as

Charophyta Charophyta () is a group of freshwater green algae, called charophytes (), sometimes treated as a division, yet also as a superdivision or an unranked clade. The terrestrial plants, the Embryophyta emerged within Charophyta, possibly from terre ...

, consisting of more than 4000 described species. It contains five orders: the Spirogloeales, the Serritaeniales, the

Zygnematales The Zygnematales ( el, ζυγός (''zygós'') and νῆμα (''nḗma'') ( nom.), νήματος (''nḗmatos'') (gen.)), also called the Conjugatales, are an order of green algae, comprising several thousand different species in two families. T ...

, the Spirogyrales, and the

Desmidiales Desmidiales, commonly called desmids (''Gr.'' ''desmos'', bond or chain), are an order in the Charophyta, a division of green algae in which the land plants (Embryophyta) emerged. Or in other words, Desmid, (order Desmidiales), order of single ...

. The Zygnematophyceae are the sister clade of the

land plants 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 siste ...

. The body plan of Zygnematophyceae is simple, and appear to have gone through a secondary loss of morphological complexity. The most basal members are unicellular, but filamentous species have evolved at least five times. They contain genes involved in protection from desiccation that appear to have been derived by

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between Unicellular organism, unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offsprin ...

from bacteria; the genes are found in plants, Zygnematophyceae, bacteria, but no other organisms. The genes may have helped to enable plants to make the transition to life on land.

Sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

in the Zygnematophyceae takes place through a process called ''

conjugation Conjugation or conjugate may refer to: Linguistics * Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics * Complex conjugation, the chang ...

''. Here cells or filaments of opposite gender line up, and tubes form between corresponding cells. The male cells then become amoeboid and crawl across the female, or sometimes both cells crawl into the connecting tube. The cells then meet and fuse to form a

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

, which later undergoes

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

to produce new cells or filaments. As in land plants, only the female passes its

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 on to the offspring.

Taxonomy

Class Zygnematophyceae * Subclass Spirogloeophycidae Melkonian, Gontcharov & Marin 2019 ** Order Spirogloeales Melkonian, Gontcharov & Marin 2019 *** Family Spirogloeaceae Melkonian, Gontcharov & Marin 2019 * Subclass Zygnematophycidae Melkonian, Gontcharov & Marin 2019 ** Family Spirogyraceae Palla 1894 ** Order

Borge & Pascher 1931 *** Family

Zygnemataceae The Zygnemataceae are a family of filamentous or unicellular, uniseriate (unbranched) green algae. The filaments are septated and reproduction is by conjugation; ''Spirogyra'' is commonly used in schools to demonstrate this kind of reproduction ...

(Meneghini) Kützing 1843 *** Family

Mesotaeniaceae The Mesotaeniaceae are a small family of unicellular green algae known as the "saccoderm desmids". The Mesotaeniaceae appear to be sister or ancestral to the Zygnemataceae. The desmids are a deep branching group of Zygnemataceae. ''Spirotaenia' ...

Oltmans 1904 (paraphyletic) ** Order

Krieger 1933 *** Family

Gonatozygaceae The Gonatozygaceae are one of four families of Charophyte green algae in the order Desmidiales (desmids). Genera , AlgaeBase accepted two genera: * ''Genicularina'' Molinari & Guiry * ''Gonatozygon'' De Bary ( syn. ''Leptocystinema'') ''Genicul ...

Fritsch 1927 *** Family

Closteriaceae The Closteriaceae are one of four families of Charophyte green algae in the order Desmidiales (desmids).See the NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a ...

Bessey 1907 ex Pritchard 1852 *** Family

Peniaceae ''Penium'' is a genus of green algae, and the sole member of the family Peniaceae.See the NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the Nationa ...

Haeckel 1894 *** Family

Desmidiaceae The Desmidiaceae are one of four families of charophyte green algae in the order Desmidiales (desmids).See the NCBIbr>webpage on Desmidiaceae Data extracted from the Genera Genera accepted by AlgaeBase were: *'' Actinodontum'' – 3 species ...

Kiitzing 1833b ex Ralfs 1845 Phylogeny

References

Green algae classes {{algae-stub