{{Short description|Species of chlorophyte green alga}} {{Speciesbox |image = Sea lettuce in Brofjorden 1 - cropped.jpg |image_caption = ''Ulva lactuca'' in Brofjorden, Sweden |image2 = Ulva lactuca - Sowerby.jpg |image2_caption = Illustration of ''Ulva lactuca'' in ''English Botany'' (Sowerby, 1790-1814) |genus = Ulva |species = lactuca |authority = L. | synonyms = *''Ulva crassa'' {{small|V. J. Chapman, 1956}} }}
'''''Ulva lactuca''''', also known by the common name sea lettuce,<ref>{{cite book |author1=David Chapman |title=Exploring the Cornish Coast |date=2008 |publisher=Alison Hodge |location=Penzance |isbn=9780906720561 |page=25}}</ref> is an edible green alga in the family Ulvaceae. It is the type species of the genus ''Ulva''. A synonym is '''''U.''' '''fenestrata''''', referring to its "windowed" or "holed" appearance.<ref>{{Cite web|last=Bates|first=Colin|date=|title=An introduction to the (macro) algae of British Columbia|url=https://ibis.geog.ubc.ca/biodiversity/eflora/algae.html|access-date=29 July 2020|website=Electronic Atlas of the Flora of British Columbia, University of British Columbia}}</ref>
==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 {{convert|18|cm|frac=4}} or more in length, though generally much less, and up to {{convert|30|cm|abbr=on}} across.<ref>{{cite web|url=http://www3.gettysburg.edu/~rcavalie/bda_i/078.html|website=Gettysburg College|title=''Ulva lactuca''|access-date=December 28, 2007|archive-date=December 18, 2007|archive-url=https://web.archive.org/web/20071218000042/http://www3.gettysburg.edu/~rcavalie/bda_i/078.html|url-status=dead}}</ref> The membrane is two cells thick, soft and translucent, and grows attached, without a stipe, to rocks or other algae by a small disc-shaped holdfast.<ref name="Burrows 91">{{Cite book|author=Burrows, E.M.|year=1991|title=Seaweeds of the British Isles|volume=2|publisher=Natural History Museum|place= London|isbn=978-0-565-00981-6}}</ref>
Green to dark green in colour, this species in the Chlorophyta is formed of two layers of cells irregularly arranged, as seen in cross-section. The chloroplast is cup-shaped in some references but as a parietal plate in others<ref name="Burrows 91"/> with one to three pyrenoids. There are other species of ''Ulva'' which are similar and not always easy to differentiate.
=== Life cycle === The sporangial and gametangial thalli are morphologically alike. The diploid adult plant produces zoospores by meiosis – making them haploid. 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.<ref name="Abbott and Hollenberg">{{Cite book |author1=Abbott, I.A. |title=''Marine Algae of California.'' |author2=Hollenberg, G.J. |publisher=Stanford University Press |year=1976 |isbn=978-0-8047-0867-8 |place=California |name-list-style=amp}}</ref><ref name="Mondragon and Mondragon 03">{{Cite book |author1=Mondragon, J. |title=''Seaweeds of the Pacific Coast.'' |author2=Mondragon, J. |publisher=Sea Challengers |year=2003 |isbn=978-0-930118-29-7 |place=Monterey, California |name-list-style=amp}}</ref><ref>"{{cite web |title=Plant Science 4 U |url=http://www.plantscience4u.com/2014/05/diplohaplontic-life-cycle-in-algae.html#.V3vOW6s7o3R |access-date=5 July 2016}}</ref>
== Distribution == 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.<ref name="Burrows 91" /><ref>{{cite web|title=''Ulva lactuca'' Linnaeus|url=http://www.algaebase.org/search/species/detail/?species_id=c1f137497a33b2948&sk=0&from=results|website=AlgaeBase}}</ref>
==Ecology== ''Ulva lactuca'' is very common on rocks and on other algae in the littoral and sublittoral on shores all around the British Isles,<ref name="Hardy and Guiry 06">{{Cite book |author1=Hardy, F.G. |author2=Guiry, M.D. |year=2006 |title=A Check-list and Atlas of the Seaweeds of Britain and Ireland |publisher=British Phycological Society |place=London |isbn=978-3-906166-35-3 }}</ref> the coast of France,<ref name="VLIZ">{{cite web |url=http://www.vliz.be/vmdcdata/tisbe/tisbe.php?p=taxdetails&id=145984 |title=Tisbe taxon details: ''Ulva lactuca'' Linnaeus, 1753 |publisher=Flanders Marine Institute (VLIZ) }}</ref> the Low Countries<ref name="VLIZ"/> and up to Denmark.<ref>{{cite journal |author1=Geertz-Hansen, O. |author2=Sand-Jensen, K. |author3=Hansen, D. F. |author4=Christiansen, A. |date=September 1993 |title=Growth and grazing control of abundance of the marine macroalga, ''Ulva lactuca'' L. in a eutrophic Danish estuary |journal=Aquatic Botany |volume=46 |issue=2 |pages=101–109 |doi=10.1016/0304-3770(93)90039-Y |bibcode=1993AqBot..46..101G }}</ref> In the Pacific Northwest, ''Ulva lactuca'' L. is distributed from Alaska to the Gulf of California.<ref>{{cite journal |last1=Hayden |first1=Hillary |last2=Waaland |first2=Robert |title=A molecular systematic study of Ulva (Ulvaceae, Ulvales) from the northeast Pacific |journal=Phycologia |volume=43 |issue=4 |pages=364–382 |date=2004-07-30 |doi=10.2216/i0031-8884-43-4-364.1 |bibcode=2004Phyco..43..364H |url=https://blakely.spu.edu/wp-content/uploads/2024/05/Hayden-Waaland-2004-Molecular-study-of-Ulva.pdf |access-date=28 January 2026 }}</ref>
It is particularly prolific in areas where nutrients are abundant.<ref>{{cite web |url=http://www.seaweed.ie/algae/ulva.html |website=The Seaweed Site |author=Michael Guiry |title=Overview of ''Ulva lactuca'' ecology |access-date=December 28, 2007}}</ref> 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.<ref name="Hirst">{{cite news |author=Hirst, Michael |date=August 11, 2009 |url=https://news.bbc.co.uk/2/hi/europe/8195180.stm |title=Toxic seaweed clogs French coast |work=BBC News |access-date=August 11, 2009}}</ref><ref name="BBCseaweed">{{cite news |url=https://news.bbc.co.uk/2/hi/europe/8242649.stm |title=Seaweed suspected in French death |work=BBC News |date=September 7, 2009 |access-date=2009-09-08}}</ref> The result is that large quantities of ''U. lactuca'' are washed up on beaches, where their decay produces methane, hydrogen sulfide, and other gases.<ref name="Hirst"/><ref>{{cite journal |author=Nedergaard, Rasmus I. |author2=Risgaard-Petersen, Nils |author3=Finster, Kai |date=August 17, 2002 |title=The importance of sulfate reduction associated with ''Ulva lactuca'' thalli during decomposition: a mesocosm experiment |journal=Journal of Experimental Marine Biology and Ecology |volume=275 |issue=1 |pages=15–29 |doi=10.1016/S0022-0981(02)00211-3|bibcode=2002JEMBE.275...15N |url=http://www.elsevier.com/locate/jembe |url-access=subscription }}</ref>
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,<ref name="bbc09">{{cite web |access-date=2009-08-11 |url=https://news.bbc.co.uk/2/hi/europe/8195180.stm |title=Toxic seaweed clogs French coast |publisher=BBC |date=2009-08-11 |author=Hirst, Michael}}</ref><ref>{{cite web |access-date=2009-08-11 |url=https://www.telegraph.co.uk/travel/travelnews/6005673/Almost-100-places-in-Brittany-have-toxic-seaweed.html |title=Almost 100 places in Brittany have toxic seaweed |publisher=Telegraph.co.uk |date=2009-08-11 |author=Samuel, Henry}}</ref> causing a major public health scare as it decomposed. The rotting thalli produced large quantities of hydrogen sulfide, a toxic gas which, like hydrogen cyanide, inhibits cytochrome c oxidase, inhibiting cellular respiration and resulting in critical cellular hypoxia. 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 of fertilizers and the excretion of nitrates by pigs and poultry.<ref name="bbc09" /> In an earlier separate incident at the same beach in July 2009, a truck driver had died near his vehicle after hauling three truckloads of sea lettuce without protective gear during the annual cleanup. Although initially recorded as a heart attack, the death of the truck driver prompted French authorities to exhume his remains for an autopsy. It was later determined to be cardiac arrest resulting from pulmonary edema, which is an indication of possible hydrogen sulfide poisoning.<ref name="BBCseaweed"/><ref>{{cite book|last1=Lymbery|first1=Philip|title=Farmageddon: The True Cost of Cheap Meat|date=2014|publisher=Bloomsbury Publishing|isbn=9781408846421|page=179}}</ref> Environmentalists claimed that dead animals found on the algae-clogged beaches (including 31 wild boars in July 2011) were a result of toxic fumes.<ref>{{cite news|last1=Chrisafis|first1=Angelique|title=Brittany beaches hit by toxic algae|url=https://www.theguardian.com/environment/2011/jul/27/brittany-beaches-toxic-algae-boars|access-date=31 December 2015|work=The Guardian|issue=27 July 2011}}</ref><ref>{{cite magazine|last1=McKenna|first1=Maryn|title=Attack of the Deadly Slime: Farm Effluent Ruins French Beaches|url=https://www.wired.com/2011/07/green-slime-beaches/|magazine=Wired|access-date=31 December 2015|date=26 July 2011}}</ref>
==Uses== In Scotland, ''U. lactuca'' is used in soups and salads.<ref name="Indergaard and Minsaas 92">{{cite book |last1=Indergaard |first1=M. |last2=Minsaas |first2=J. |year=1991 |chapter= |editor-last1=Guiry |editor-first1=M. D. |editor-last2=Blunden |editor-first2=G. |title=Seaweed Resources in Europe: Uses and Potential |volume=107 |pages=395–396 |doi=10.1016/0044-8486(92)90086-Z |language=en }}</ref><ref>{{cite web |url=http://www.mbari.org/staff/conn/botany/greens/anna/frontpages/recipes.htm |website=Monterey Bay Aquarium Research Institute |title=Ulva Recipes|access-date=December 28, 2007 |url-status=dead |archiveurl=https://web.archive.org/web/20080102053143/http://www.mbari.org/staff/conn/botany/greens/anna/frontpages/recipes.htm |archivedate=January 2, 2008 }}</ref> In Hawaiʻi, ''U. lactuca'' is also called limu pālahala and eaten in different ways: mixed with other algae, salted and served with raw fish, boiled in water and served as a soup, or served with chili pepper, onions, soy sauce and sugar.<ref name="hawaiian seaweeds">{{Cite book |last=Aiona |first=Abbott, Isabella |title=Limu : an ethnobotanical study of some Hawaiian seaweeds |date=1996 |publisher=National Tropical Botanical Garden |oclc=34798092}}</ref> Additionally, ''U. lactuca'' has traditional uses in Hawaiʻi as fertilizer and as adornment for hula.<ref name="hawaiian seaweeds" /> When ''U. lactuca'' is used for hula it is called limu pāpahapaha.<ref name="hawaiian seaweeds" />
As an alternative to vegetable oil crops, ''U. lactuca'' can be a source of biofuels, suitable for transesterification in biodiesel production, and does not require arable land and fertilizers. It can grow in saline and waste water and has a higher ability in sequestering atmospheric carbon dioxide than terrestrial energy crops.<ref>{{cite journal | last1 = Dominguez | first1 = Herminia | last2 = Loret | first2 = Erwann P. | title = Ulva lactuca, a Source of Troubles and Potential Riches | journal = Marine Drugs | date = March 2019 | volume = 17 | issue = 6 | pages = 357 | doi = 10.3390/md17060357 | doi-access = free| pmid = 31207947 | pmc= 6627311 | bibcode = 2019MarDr..17..357D }}</ref>
==References== {{Reflist|2}}
==Further reading== * Hayden, H.S., Blomster, J., Maggs, C.A., Silva, P.C., Stanhope, M.J. and Waaland, J.R. (2003) [http://www.biosciences.bham.ac.uk/labs/callowj/ent/Hayden_Blomster_Maggs.pdf "Linnaeus was right all along: ''Ulva'' and ''Enteromorpha'' are not distinct genera"] {{Webarchive|url=https://web.archive.org/web/20081015140243/http://www.biosciences.bham.ac.uk/labs/callowj/ent/Hayden_Blomster_Maggs.pdf |date=2008-10-15 }} ''European Journal of Phycology'' 38: pp. 277–294, {{doi|10.1080/1364253031000136321}}
==External links== * [http://www.algaebase.org/search/species/detail/?species_id=39&sk=0&from=results ''Ulva lactuca''], AlgaeBase entry * [https://web.archive.org/web/20060911143925/http://omp.gso.uri.edu//doee/biota/algae/chloro/ulva.htm ''Ulva lactuca''], University of Rhode Island
{{Taxonbar|from=Q852879}}
Category:Edible seaweeds Category:Ulvaceae Category:Algae of Australia Category:Plants described in 1753 Category:Botanical taxa named by Carl Linnaeus