Spirogyra cells contain chloroplasts, a large vacuole, a cell nucleus, cytoplasmic strands holding the nucleus in place and two cell walls. They are simple plants, with no specialized cells for absorbing water, transporting nutrients or reproduction.
The feature for which the genus is named is the spiral chain of chloroplasts that almost fills each cell. The chloroplasts wind themselves around the central vacuole in which the cell nucleus is suspended by cytoplasmic strands. The vacuole is filled with water and keeps the cell inflated, so the chloroplasts have more surface area for light absorption.
Spirogyra are considered unicellular plants even though they typically are found in long, free-floating filaments. This is because although the cells group themselves together, there is no communication or transport between the cells, as there is in multicellular organisms such as trees or grasses. Each spirogyra cell is a unit unto itself.
The distinctive, fine green filaments give spirogyra the common names "mermaid's tresses" and "water silk." Spirogyra cells arrange themselves end to end, with filaments being only one cell thick. As in more complex plants, the outer cell wall is made of cellulose, giving the strands a tough outer covering; although, their thinness makes them rather delicate. The second inner wall is made of pectin, a fibrous organic molecule commonly found in fruit.