What green algae is also called "sea lettuce"?

The correct choice is Ulva, commonly referred to as "sea lettuce." This green algae gets its nickname due to its thin, leafy appearance that resembles that of a lettuce leaf. Ulva is easily recognized by its vibrant green color and its frond-like structure, which can grow in both marine and brackish environments.

Ulva is significant ecologically as it provides a habitat and food source for various marine organisms and plays a role in nutrient cycling within aquatic ecosystems. It can also be consumed by humans and is rich in vitamins and minerals, often used in salads or as an ingredient in various dishes.

Other algae mentioned do not share this specific identification: Chlamydomonas is a unicellular green algae, Codium, also known as "dead man's fingers," has a different morphology and is typically found in marine environments, while Spirulina is a cyanobacterium (often referred to as blue-green algae) known for its health benefits and nutrient density. Each of these has distinct characteristics that differentiate them from Ulva, reinforcing why Ulva is accurately identified as "sea lettuce."