Desmidiales

Desmids (Gr. desmos, bond or chain) are an order (Desmidiales) in the Charophyta, a division of green algae that forms a sister group to the land plants (Embryophyta).

The desmids are often treated as members of the Zygnematales, as family Desmidiaceae. The Desmidiales comprise around 40 genera and 5,000 to 6,000species, found mostly but not exclusively in fresh water. Many species may be found in the fissures between patches of sphagnum moss in marshes. With a pH level of approximately 4.0, sphagnum peat provides the ideal environment for this flora.

The structure of these algae is unicellular, while the cell is sometimes divided into two symmetrical compartments separated by a narrow bridge or isthmus, wherein the spherical nucleus is located. Each semi-cell houses a large, often folded chloroplast for photosynthesizing. One or more pyrenoids can be found. These form carbohydrates for energy storage.

Desmids assume a variety of highly symmetrical and generally attractive shapes, among those elongated, star-shaped and rotund configurations, which provide the basis for their classification. The largest among them may be visible to the unaided eye.