Spirogyra (pond silk) belongs to the division Chlorophyta. Spirogyra is a green algae.

Asexual reproduction in Spirogyra mirabilis takes place by aplanospores. Under unfavourable conditions, the protoplast of each vegetative cell shrinks and develops a wall around it to form an aplanospore. Each non-motile aplanospore germinates to form a new filament.

Under unfavourable conditions, the vegetative cells of S. farlowii develop thick-walled cells called akinetes. After getting favourable conditions, each akinete germinates into a new filament.

Sclariform conjugation takes place when filaments lie parallel to each other.

Scalariform conjugation takes place at night.

Direct lateral conjugation is seen in S. jogensis.

Pectin forms the outer cell wall of Spirogyra.

Spirogyra is unbranched, i.e. it is a linear filament with no branching.

In lateral conjugation, male and female gametes are present in the same filament. Male and female gametes are present in two adjacent cells, which conjugates to form a diploid zygospore.

The pyrenoid structures of Spirogyra stores starch.

Zygospores are the product of sexual reproduction. It is the only diploid phase of Spirogyra cell cycle.

Spirogyra is eutropic as it is highly rich in nutrients.

Scalariform conjugation leads to formation of a single Spirogyra strand.

Each cell of Spirogyra contains 1-16 chloroplasts.

Two parallel strands of Spirogyra united with each other by a conjugation tube is referred to as aplanogametangia.