Description: Ulva lactuca is a thin flat green alga growing from a discoid holdfast. The margin is somewhat ruffled and often torn. It may reach 18cm or more in length, though generally much less, and up to 30 cm across. The membrane is two cells thick, soft, translucent and grows attached, without a stipe, to rock by a small disc-shaped holdfast. Green to dark green in color this species in the Chlorophyta is formed of two layers of cells irregularly arranged, as seen in cross section. The chloroplast is cup-shaped with 1 to 3 pyrenoids. There are other species of Ulva which are similar and not always easy to differentiate.
Habitat: This sea lettuce is found in all levels of the intertidal. However, in more northerly latitudes and brackish habitats, it is found in the shallow sub littoral. In very sheltered conditions, the plants that have become detached from the substrate can continue to grow, forming extensive floating communities. Ulva lactuca can be found on suitable substrata in estuaries. It is particularly prolific in areas where nutrients are abundant.