Green algae

The green algae (Chlorophyta) are a monophyletic group that includes the multicellular land plants (Plantae). Like the plants, they have cellulose cell walls, and chloroplasts with chlorophylls a and b.

Contents

Pediastrum
Scenedesmus
Coelastrum
Desmids
Chlamydomonas
Dictyosphaerium
Spirogyra
Others


Pediastrum

Common in ponds and other freshwater habitats. They form star-shaped (stellate) plates of cells which may or may not be net-like (reticulate).


Scenedesmus

Cells arranged in groups of four, each cell spindle-shaped with tapered ends. They may or may not have spines emerging from the tips of the end-cells. In some species, the cells are arranged in rows, while in others they are alternating or diagonally arranged, but always with lateral sides touching.


Coelastrum

These appear to be the same species of Coelastrum but at different stages. The colony forms a hollow ball, each cell being connected to its neighbors by protrusions of the cell wall. The regularity of the cell arrangement is geometrically pleasing. The daughter colonies are smaller and appear to be generated within the cells of the original mother colony.


Desmids

These are diverse in form but all have a constriction (which may be strong or shallow) that divides each cell into two semi-cells. Cell division begins at the constriction point and results in the formation of a new semi-cell to complement each of the original two. They are formally classified as members of the family Desmidiaceae. A Dutch group has put together a useful webpage on the desmids of the Netherlands.

Staurastrum

The cell looks like a caltrop, with each semi-cell having three-points. The ridges of bumps that ornament the surface can be more easily seen in an empty cell wall.

Closterium

Banana-shaped desmids with a large chloroplast per semi-cell.

Pleurotaenium

Looks at first glance to be a filamentous alga, but like the rest of the desmids it only has two semi-cells, joined at the middle by a constriction that is flanked by “bumps” on either side.

Brownian motion is evident in parts of the cytoplasm, as shown in this video:

Cosmarium

Rather nondescript desmids, with rounded and compressed semi-cells when seen from the side. The one that looks like a dumbbell, with a prominent middle constriction, is in the subgenus Dysphinctium, section Eudysphinctium.

The zygotes of desmids may look quite different from the vegetative cells:


Chlamydomonas

Green single-celled alga with two equal flagella, a large chloroplast, and red eye-spot.

The flagellated green cell below may be a Chlamydomonas but there is only one flagellum – perhaps this is a defective cell?


Dictyosphaerium

Forming colonies in multiples of four. Each set of four are the daughter cells of a single mother cell, whose cell wall persists as the thread-like strands connecting its daughters. Individual cells are small, ovoid, and have cup-shaped chloroplasts.


Spirogyra

Easily recognizable by the helically-wound chloroplasts with prominent pyrenoids. Common in freshwater around the world.


Others

Filamentous green alga with one cell differentiated into an oogonium, the female structure for sexual reproduction.

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