Ulva lactuca is commonly called sea lettuce. Its color can range from light yellowish green to darker green, but is most commonly a vivid green underwater. Ulva lactuca is cellophane thin (only two cell layers thick), and forms light yellowish green to dark green translucent sheets. The soft frond grows as a single, irregular, but somewhat round shaped blade with slightly ruffled edges which are often torn. There can be numerous small holes or perforations scattered throughout. The frond is connected to rocks with a small, almost invisible discoid holdfast, and does not have a stipe. Ulva lactuca may grow to a diameter of 20 to 30 centimeters, although it is freqently much smaller, with larger sheets feeling slightly thicker than smaller specimens.

Cited from:

Pereira, L. 2012. MACOI, Portuguese Seaweeds Website. World-wide Electronic Publication. IMAR, Department of Life Sciences, University of Coimbra, http://macoi.ci.uc.pt.