Zygnematales
| Zygnematales | |
|---|---|
 |
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| Spirogyra green algae | |
| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Charophyta |
| Class: | Zygnematophyceae |
| Order: |
Zygnematales C.E.Bessey, 1907 |
| Families | |
| Synonyms | |
|
Zygnematales Borge and Pascher, 1913 |
|
Zygnematales Borge and Pascher, 1913
The Zygnematales (Greek: ζυγός (zygos) + νήμα (nēma) (nom.), νήματος (nēmatos) (gen.)), also called the Conjugatales, are an order of green algae, comprising several thousand different species in two families. The larger family Zygnemataceae, with well-known genera such as Zygnema and Spirogyra, includes members that grow as unbranched filaments, which grow longer through normal cell division. The smaller family Mesotaeniaceae includes the saccoderm "desmids", a group of unicellular species that were formerly classified with the "true" desmids. Most members of both families live in freshwater, and form an important component of the algal scum that grows on or near plants, rocks, and various debris.
Systematically they fall within the division Charophyta, which includes the groups of algae that are most closely related to the higher plants. Charophyta are included with land plants (Embryophyta) in the clade Streptophyta.
Sexual reproduction in Zygnematales takes place through a process called conjugation. Here filaments of opposite gender line up, and tubes form between corresponding cells. The male cells then become amoeboid and crawl across, or sometimes both cells crawl into the tube. The cells then meet and fuse to form a zygote, which later undergoes meiosis to produce new filaments. As in plants, only the female passes chloroplasts on to the offspring.
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