Ulva lactuca, also known by the common name sea lettuce, 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.

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 or more in length, though generally much less, and up to across. 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.

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

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.

Ecology

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

In the Pacific Northwest, Ulva lactuca L. is distributed from Alaska to the Gulf of California.

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 U. lactuca are washed up on beaches, where their decay produces methane, hydrogen sulfide, 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 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. Environmentalists claimed that dead animals found on the algae-clogged beaches (including 31 wild boars in July 2011) were a result of toxic fumes.

Uses

In Scotland, U. lactuca is used in soups and salads. 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.

Additionally, U. lactuca has traditional uses in Hawaiʻi as fertilizer and as adornment for hula.

References

Further reading

  • 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,
  • Ulva lactuca, AlgaeBase entry
  • Ulva lactuca, University of Rhode Island