Ulva (alga)
Edible green algae widely distributed in world oceans.
The genus *Ulva* includes the sea lettuces, a group of edible green algae found along coastlines worldwide. Its type species is *Ulva lactuca*—*lactuca* meaning "lettuce" in Latin. This genus also contains species once classified under *Enteromorpha*, which are commonly called green nori.
Individual blades can exceed 400 mm (16 in) in size, but only in sheltered areas. The alga is light to dark green, attached by a disc-shaped holdfast, and its structure is a flattened, leaflike thallus.
Sea lettuce is eaten by various marine animals, including manatees and sea hares. Humans in Scandinavia, Great Britain, Ireland, China, and Japan (where it is called aosa) also consume it, raw in salads or cooked in soups. It is rich in protein, soluble dietary fiber, vitamins, and minerals—especially iron. Chopped and mixed into bread dough before baking, it enhances flavor and fortifies the bread. However, contamination with toxic heavy metals at certain collection sites makes it unsafe for human consumption.
In August 2009, massive amounts of this alga washed onto beaches in Brittany, France, creating a public health crisis as it decomposed. Rotting leaves released large quantities of hydrogen sulfide, a toxic gas. In one incident near Saint-Michel-en-Grève, a horse rider lost consciousness and his horse died after inhaling the fumes; in another, a truck driver hauling decomposing sea lettuce passed out, crashed, and died, with toxic fumes cited as the cause. Environmentalists attributed the event to excessive nitrogenous compounds from improper disposal of pig and poultry slurry from industrial farms, as well as chemical fertilizers and slurry used in arable farming.
Species in the genus include accepted species, as well as *nomina dubia* such as *Ulva costata*, *Ulva repens*, and *Ulva tetragona*. A newly discovered Indian endemic species with a tubular thallus indistinguishable from *Ulva intestinalis* was formally established in 2014 as *Ulva paschima*. Ten new species have been found in New Caledonia: *Ulva arbuscula*, *Ulva planiramosa*, *Ulva batuffolosa*, *Ulva tentaculosa*, *Ulva finissima*, *Ulva pluriramosa*, *Ulva scolopendra*, and *Ulva spumosa*.
Quick Facts
- Taxon
- Ulva
Facts from the source article.
Lore & Background
Individual blades of Ulva can grow to more than 400 mm in size, but this occurs only in sheltered areas. The alga is macroscopic, light to dark green in color, and attached by a disc holdfast, with a leaflike flattened thallus. Sea lettuce is eaten by various sea animals, including manatees and sea hares. Many species are a food source for humans in Scandinavia, Great Britain, Ireland, China, and Japan, where it is known as aosa. It is eaten raw in salads and cooked in soups, and is high in protein, soluble dietary fiber, and vitamins and minerals, especially iron. It can enhance flavor and fortify bread when chopped and mixed into dough before baking. However, contamination with toxic heavy metals at certain collection sites makes it dangerous for human consumption. In August 2009, unprecedented amounts washed up on beaches of Brittany, France, causing a public health scare as decomposing leaves produced large quantities of hydrogen sulfide, a toxic gas. Incidents included a horse rider losing consciousness and his horse dying, and a lorry driver passing out, crashing, and dying from toxic fumes. Environmentalists blamed excessive nitrogenous compounds from improper disposal of pig and poultry slurry and chemical fertilizers.
Reader's Guide
The genus Ulva holds significance as a widely distributed, edible green alga with both ecological and human uses. Ecologically, it serves as food for marine animals such as manatees and sea hares. For humans, it is consumed in multiple regions including Scandinavia, Great Britain, Ireland, China, and Japan, where it is eaten raw or cooked and valued for its nutritional content—high in protein, soluble dietary fiber, and vitamins and minerals, particularly iron. It is also used to enhance flavor and fortify bread. However, its legacy includes serious health concerns: contamination with toxic heavy metals at certain sites makes it dangerous for consumption, and in August 2009, massive blooms on Brittany's beaches produced hydrogen sulfide gas, leading to human and animal fatalities. These events were linked to agricultural runoff. The genus also encompasses species formerly in Enteromorpha, known as green nori, and includes newly discovered species such as the Indian endemic Ulva paschima and ten new species from New Caledonia. The type species is Ulva lactuca, whose name reflects its lettuce-like appearance.
Did You Know?
- The type species of Ulva is Ulva lactuca, with lactuca meaning 'lettuce' in Latin.
- Individual blades can exceed 400 mm in sheltered areas.
- In Japan, sea lettuce is known as aosa.
- In August 2009, decomposing Ulva on Brittany beaches produced toxic hydrogen sulfide gas, causing fatalities.
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