Zygnematales

Zygnematales
Spirogyra green algae
Scientific classification
(unranked):	Viridiplantae
(unranked):	Charophyta
Class:	Zygnematophyceae
Order:	Zygnematales C.E.Bessey, 1907
Families
Zygnemataceae Mesotaeniaceae

The Zygnematales (

, and form an important component of the algal scum that grows on or near plants and rocks.

Systematically they fall within the division Charophyta/Streptophyta, in which the land plants (Embryophyta) emerged.^[2]

Sexual reproduction in Zygnematales takes place through a process called conjugation.^[3] 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.^[4]

Other conjugating algae are the Mesotaeniaceae, sister of the Zygnematales, and Spirotaenia, a basal green algae. Additionally, the Desmidiales appear to have emerged deep within the Zygnematales, and are also conjugating.^[5]

Gallery

• 
  Netrium oblongum.  A saccoderm "desmid"
• 
  Single Spirogyra cell
• 
  Spirogyra.  Each numbered tick = 122 μM
• 
  Spirogyra.  Each numbered tick = 20 μM
• 
  Microscopic view of Spirogyra conjugation
• 
  Zygnema.  Each numbered tick = 122 μM
• 
  Zygnema.  Each numbered tick = 20 μM

References