There are about 6,000 species of green algae. Many green algae are single cells. Others form groups of cells or are seaweeds. Like plants, most green algae use sunlight to make their own food. Spirogyra grows in water as long strings of cells. These large groups of cells are slimy and often called “pond scum.”
Spirogyra is a filamentous green algae that can often form flimsy green aggregates in freshwater ponds. It is distinguished by having unbranched filaments and with chloroplasts forming a spiral ribbon just under the cell surface. This gives a coiled or twisted texture to the cells, and it is from this appearance that the organism gets its name (Greek speira, “coil” + gyros, “twisted”) The cell wall is characteristically straight and parallel-sided. The single chloroplast usually almost fills the length of the cell.