Ulva lactuca is a thin flat green alga growing from a discoid holdfast. The margin is somewhat ruffled and often torn. It may reach 18 cm or more in length, though generally much less, and up to 30 cm across. The membrane is two cells thick, soft and 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.
The distribution is worldwide: Europe, North America - west and east coasts, Central America, Caribbean Islands, South America, Africa, Indian Ocean Islands, South-west Asia, China, Pacific Islands, Australia and New Zealand. 
Ulva lactuca is very common on rocks and on other algae in the littoral and sublittoral on shores all around the British Isles, the coast of France, the Low Countries and up to Denmark. It is particularly prolific in areas where nutrients are abundant. This has been the case off the coast of Brittany where a high level of nitrates, from the intensive farming there, washes out to sea. The result is that large quantities of Ulva lactuca are washed up on beaches, where their decay produces methane, hydrogen sulphide, and other gases.
Certain environmental conditions can lead to the algae spreading over large areas. In August 2009, unprecedented levels of the algae washed up on the beaches of Brittany, France, causing a major public health scare as it decomposed. The rotting thalli produced large quantities of hydrogen sulphide, a toxic gas. In one incident near Saint-Michel-en-Grève, a horse rider lost consciousness and his horse died after breathing the seaweed fumes. Environmentalists blamed the phenomenon on excessive use fertilizers and the excretion of nitrates by pig and poultry farmers. In a separate incident at the same beach, a truck driver died after taking part in the cleanup without protection.
The sporangial and gametangial thalli are morphologically alike. The diploid adult plant produces haploid spores by meiosis, these settle and grow to form haploid male and female plants similar to the diploid plants. When these haploid plants release gametes they unite to produce the zygote which germinates, and grows to produce the diploid plant.
- ^ "Ulva lactuca". Gettysburg College. http://www3.gettysburg.edu/~rcavalie/bda_i/078.html. Retrieved 2007-12-28.
- ^ "Ulva lactuca". University of Rhode Island. http://omp.gso.uri.edu/doee/biota/algae/chloro/ulvaxf.htm. Retrieved 2007-12-28.
- ^ Burrows, E.M. (1991) Seaweeds of the British Isles. Volume 2 Chlorophyta. Natural History Museum, London. ISBN 0 565 00981 8
- ^ "Sea lettuce, Ulva". University of Auckland. http://www.sbs.auckland.ac.nz/uoa/science/about/departments/sbs/newzealandplants/maoriuses/food/seaweeds/sea-lettuce-ulva.cfm. Retrieved 2009-07-03.
- ^ Hardy, F.G. and Guiry, M.D. (2006). A Check-list and Atlas of the Seaweeds of Britain and Ireland. British Phycological Society, London. ISBN 3 906166 35 X
- ^ a b "Tisbe taxon details: Ulva lactuca Linnaeus, 1753" Flanders Marine Institute (VLIZ)
- ^ Geertz-Hansen, O.; Sand-Jensen, Kaj ; Hansen, D. F. and Christiansen, A. (1993) "Growth and grazing control of abundance of the marine macroalga, Ulva lactuca L. in a eutrophic Danish estuary" Aquatic botany 46(2): pp. 101-109,
- ^ Michael Guiry. "Overview of Ulva lactuca ecology". the Seaweed Site. http://www.seaweed.ie/algae/ulva.lasso. Retrieved 2007-12-28.
- ^ a b Hirst, Michael (11 August 2009) "Toxic seaweed clogs French coast" BBC News, accessed 11 August 2009
- ^ "Seaweed suspected in French death". BBC News. 07 September 2009. http://news.bbc.co.uk/2/hi/europe/8242649.stm. Retrieved 2009-09-08.
- ^ Nedergaard, Rasmus I.; Risgaard-Petersen, Nils and Finster, Kai (17 August 2002) "The importance of sulfate reduction associated with Ulva lactuca thalli during decomposition: a mesocosm experiment" Journal of Experimental Marine Biology and Ecology 275(1): pp. 15-29, doi:10.1016/S0022-0981(02)00211-3
- ^ a b Hirst, Michael (2009-08-11). "Toxic seaweed clogs French coast". BBC. http://news.bbc.co.uk/2/hi/europe/8195180.stm. Retrieved 2009-08-11.
- ^ Samuel, Henry (2009-08-11). "Almost 100 places in Brittany have toxic seaweed". Telegraph.co.uk. http://www.telegraph.co.uk/travel/travelnews/6005673/Almost-100-places-in-Brittany-have-toxic-seaweed.html. Retrieved 2009-08-11.
- ^ Abbott, I.A. and Hollenberg, G.J. (1976). Marine Algae of California. Stanford University Press, California. ISBN 0 8047 0867 3
- ^ Mondragon, J. and Mondragon, J. (2003). Seaweeds of the Pacific Coast. Sea Challengers, Monterey, California ISBN 0 930118 29 4
- ^ Life-history diagram for Ulva lactuca, MBARI, accessed 13 June 2007
- ^ Indergaad, M and Minsaas, J. 1991 in Guiry, M.D. and Blunden, G. 1991. Seaweed Resources in Europe: Uses and Potential. John Wiley & Sons ISBN 0 471 92947 6
- ^ "Ulva Recipes". Monterey Bay Aquarium Research Institute. http://www.mbari.org/staff/conn/botany/greens/anna/frontpages/recipes.htm. Retrieved 2007-12-28.
- Hayden, H.S., Blomster, J., Maggs, C.A., Silva, P.C., Stanhope, M.J. and Waaland, J.R. (2003) "Linnaeus was right all along: Ulva and Enteromorpha are not distinct genera" European Journal of Phycology 38: pp. 277-294, doi: 10.1080/1364253031000136321