Ulva - commonly known as sea lettuce, brackish water green algae, marine species often found attached to rocks, serves as a food source for many marine organisms, the thallus is flat and blade-like and is composed of two layers of cells. There is no differentiation into tissues; all the cells of the plant are more or less alike except for the basal cells, which are elongated to form attachment rhizoids. Each cell contains one nucleus and has a cup-shaped choroplast with a single pyrenoid.
For other references and photos, please consult the web sites below.
http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html
For more infromtaion, please see