The genus Porphyra is a large group of red seaweeds with about 130 species worldwide. At least seven Porphyra species are said to frequently occur in the Gulf of Maine and southern New England. P. umbilicalis, P. purpurea, P. linearis, P. leucosticta, and P. dioica are the species most likely to be harvested in the Atlantic for consumption. They are very similar in appearance and challenging to differentiate in the field, so genetic analysis is usually required to identify them with any certainty. P. umbilicalis, the species sold by Maine Coast Sea Vegetables, is considered to be the most widely distributed and commercially significant Porphyra species in the North Atlantic.
All Porphyra varieties have a very thin, membranous thallus (frond) with a sheetlike appearance. The fronds are surprisingly tough despite being just 1-2 cells thick. They have no stipe (stem) and the single irregularly shaped, broad frond emerges directly from a very small but tenacious discoid holdfast. P. umbilicalis is of modest size, generally no more than 20cm (8”) long, as opposed to P. miniata and P. amplissima, which can be 30cm to 90cm long (1-3 ft). Young plants can appear to be dark green, but they become dark purplish-red as they grow and appear black when dried. P. umbilicalis grows attached to rocks or shells as a single specimen or in dense colonies. When exposed at low tide the plants can be found draped onto rock faces as thin sheets resembling polyethylene film or plastic bags. When submerged, however, Porphyra has a graceful, undulating appearance that gives off flashes of radiance from rays of sun.
Scientific & Common Names
The genus name Porphyra comes from the ancient Greek word porphura, meaning purple, and the species name umbilicalis comes from the Latin word umbilical, meaning “of the naval” in reference to how the frond is slightly pinched where it emerges from the center of the holdfast. P. umbilicalis is commonly known as laver or purple laver. In Ireland and Wales, which have a long history of using laver as food, it’s variously known as slake, sleabahn, sleabhac, or slough. P. umbilicalis is also often called nori or wild Atlantic nori because it’s similar to several Asian Porphyra and Pyropia nori species. The terms nori, laver, and purple laver are often applied interchangeably between North Atlantic and Pacific species, but we prefer to use the names laver or purple laver for P. umbilicalis.
Several other Porphyra species can be found along the same coastlines as P. umbilicalis and some of these are also harvested and eaten as laver. Through centuries of use local coastal inhabitants have come to know them by different common names. In Norway, P. umbilicalis is known as tough laver, P. purpurea as purple laver, and P. dioica as black laver. P. umbilicalis is also called tough laver in Galloway, Ireland. The other two kinds of laver found in Galloway are winter laver (P. linearis) and pale patch laver (P. leucosticta), which often grows as an epiphyte on pip grass and serrated wrack.
Porphyra species as a whole have undergone extensive reevaluation in recent years using modern genetic methods, resulting in the reclassification and renaming of some species. The Asian nori species Pyropia yezoensis, for example, was formerly known by the genus name Porphyra. In order to avoid uncertainty, scientists will sometimes use the term Porphyra sensu latu to refer to the grouping in a broad sense.
Life History & Ecology
Porphyra umbilicalis is a North Atlantic species found on both the North American and European coasts. In Europe it occurs from Northern Portugal up to the Faroe Islands. Purple laver is especially common in the United Kingdom, where it has a long tradition of human use. It’s also well known in Iceland. In North America, it’s been found south to Rhode Island and north to Prince Edward Island.
Laver grows on rocky substrata from the middle to high intertidal zones. It is wave resilient and can grow along open, exposed coastlines. Laver is tough and highly adaptable, tolerating frequent stretches of air exposure, desiccation, temperature extremes, and strong waves. It’s often found growing on rocks in sand swept areas, that is, beaches with a mix of rock and sand. The sand scours the rocks during high surf, preventing colonization by most other algal species. The resiliency of P. umbilicalis helps it colonize upper tidal zones where other seaweed species cannot survive.
Porphyra species have some of the most complex life cycles of all living organisms. The great phycologist Kathleen Drew-Baker was the first to elucidate the full life history of P. umbilicalis, in the late 1940’s. Her discovery was applied to grow Japanese Porphyra seedlings and enable the nori aquaculture industry to significantly expand there. A full understanding of the Porphyra life-cycle allowed Japanese nori farmers to predictably seed nori nets in the hatchery. Japan named Drew-Baker “Mother of the Sea” for this discovery and honored her with a monument in Tokyo that’s the site of an annual festival to this day.
Purple laver is an annual plant that almost completely disappears throughout much of its range for 3-4 months in the summer before mysteriously reappearing towards the end of autumn. Naturalists, scientists, and coastal residents had long known that laver produced spores, but until Kathleen Drew-Bakers’ work no one had been able to grow the spores in the lab and it wasn’t known how the next generation emerged. It took Drew-Baker nine years of painstaking research to figure out how laver spores produced the next generation of plants.
Like many great scientific discoveries, serendipity played a role when Drew-Baker included oyster shells in her aquaria with laver on a whim. She observed a pinkish, sludgy growth emerge on the shells after laver spore release. Scientists had observed these shell growths before in the wild but mistaken them as an entirely different species of algae, which they had named Choncocelis rosea. Dr. Drew-Baker discovered that this growth was actually another stage of laver, where the spores developed into a calcium-boring filamentous phase that germinated only after settling on shell and boring into it. This phase is now known as the chonchocelis. This type of life cycle is known as a heteromorphic alternation of generations, where each generation assumes an entirely different physical form.
Drew-Baker was able to work out laver’s full life cycle with this discovery. She determined that the laver fronds so long prized as food were dioecious gametophytes, producing eggs and sperm on separate plants. Fertilized egg cells (caropogonium) remain on the blade of the plant and develop into packets of carpospores that are released into the environment. These then develop into the conchocelis phase and settle onto shell material. After a few months of growth, conchocelis sporelings grow into small, roseate sprouts that then produce and release conchospores into the water. These 2nd generation spores are less selective about what they attach to; in nature it’s usually on rock faces, but in the lab, they will attach to twine or nets, which is a useful trait for aquaculture. Once attached, the conchospores grow into mature purple laver gametophytes that we harvest for food.
European populations of purple laver are now known to reproduce both sexually and asexually, whereas North American populations are only known to reproduce asexually. Scientists don’t yet know why this is the case, though they speculate that P. umbilicalis may have colonized the NW Atlantic from Europe through asexual reproduction, shortly after the latest glacial epoch. Perhaps asexual reproduction allowed single plants that drifted over from Europe to the new world to proliferate even in the absence of other plants nearby for sexual reproduction.
Asexual reproduction occurs when fronds produce and release “neutral spores”, which are essentially a clone of the parent frond, into the environment. Neutral spores may drift short distances before settling and germinating. Asexual reproduction appears to occur year-round in the Gulf of Maine, although the spores are less viable in the summer. Once established, the germlings are capable of fast growth and become mature within one year.
University of Maine researchers seeding scallop shells with nori conchocelis
History of Use
The first written mention in European accounts of laver as food dates back to the 12th century. In 1188, Giraldus Cambrensis (Gerald of Wales) completed an epic 600-mile trek around Wales and began writing Descriptio Cambriae, one of the earliest known travel books. Regarded as one of the great personalities of the twelfth century, Gerald of Wales mentions that during his travels he observed Welsh people eating laver gathered from the coast.
In 1607, the custom of gathering and preparing “lhawvan” (laver) in the spring along the Pembrokeshire Coast is described in fuller detail in William Camden’s Brittania. He describes how the alga is washed, cooked by “sweating” between tile stones, shredded, and kneaded into rolls or “black butter”. This is the first written description of laverbread. Fortunately, the process has been simplified over the years and laverbread can even be made from dried laver, as we’ll describe later in this account.
Harvesting laver and making it into laverbread was mostly just a homestead custom until the wreck of the American sailing vessel Thomas M Reed in 1879 along the Pembrokeshire coast. Her cargo consisted of over one million tins of Columbia River salmon, 257 cases of beef, several tons of copper and lead ore, 214 sacks of mother-of-pearl shells, and 1,000 tons of wheat. The wreckage attracted thousands of visitors and scavengers, and some among them spotted a natural treasure just beyond the wreckage…acres and acres of abundant laver seaweed. This led to a commercial enterprise where local women gathered laver and sent it to Swansea for processing and distribution as fresh or canned laverbread. Fresh laverbread has a shelf life of about one week and canned of about one year.
Laverbread became a breakfast staple for coal pit mine workers in Wales in the eighteenth century and was more broadly enjoyed throughout Wales, Ireland, and the UK. In addition to being a major producer of laverbread, Swansea was famous for being near the abundant cockle beds of Burry Port inlet. Cockles and laverbread were often eaten together and are still regarded as icons of Welsh cuisine.
Today, the custom of homemade laverbread has declined somewhat but it’s still eaten throughout Wales and some companies still make it, including Selwyn’s Seaweed Ltd, located in the laverbread mecca of Swansea. Another Pembrokeshire company that uses laver is Barti, makers of a spiced rum infused with locally gathered laver. Maine Coast Sea Vegetables is proud to be one of just a handful of companies around the world still offering sustainably wild harvested dried purple laver.
The most famous culinary use for laver continues to be laverbread, which can be made from dried laver as well as fresh. This recipe shows how to make a version of old-fashioned laverbread cakes from dried laver (just substitute our dried laver leaf or flakes for the nori sheets indicated in the recipe). Beyond laverbread, though, laver is a very versatile sea vegetable that can be used in any number of recipes. Purple laver is best when lightly roasted, as this enhances its nutty, almost sweet flavor. Once it’s roasted it can be crumbled into soups, grains, salads, and popcorn. It’s delicious toasted with pumpkin seeds, or included in omelets, rice recipes, or salads, to name just a few culinary uses. Our book Sea Vegetable Celebration includes over a dozen recipes containing laver.
Many people are quite familiar with the flat nori sheets often used to wrap sushi. Nori sheets are made from purple laver’s Asian relatives, mostly Pyropia yezoensis and Pyropia tenera, which have a mild, somewhat nutty flavor similar to purple laver. Dried purple laver flakes, or any dried seaweed flakes for that matter, can be used to make artistic nori sheets from scratch, as shown in this YouTube video.
Nutritional & Medicinal Attributes
Like other sea vegetables, purple laver contains nutritionally important minerals such as calcium, iron, magnesium, manganese, and zinc. Most Porphyra and Pyropia species are also high in protein; purple laver is about 40% protein on a dry weight basis, and gram for gram it contains more protein than animal sources such as beef or chicken. Laver protein is exceptionally well balanced with every essential amino acid. Laver is also low in fat (less than 2%) and high in fiber (about 30%).
Laver is relatively low in iodine compared to other edible seaweeds, though it’s still a good source. Laver’s iodine content is about 75µg per gram, lower than any other species sold by MCSV with the exception of sea lettuce. The moderate amount of iodine in laver can make it a preferred choice for those with iodine sensitivity. Even so, a 1 Tbs serving (about 2-3 grams) of laver flakes contributes over 100% of the RDI for iodine. One reason laverbread was so popular with Welsh miners was because it was known to prevent goiter, a common symptom of iodine deficiency.
Laver reputedly contains vitamin B12, which would make it one of the few vegetable sources of this essential vitamin. Vitamin B12, also known as cobalamin, is required for proper red blood cell formation, neurological function, and DNA synthesis. Cobalamin is synthesized by bacteria but not by plants or animals. Ruminant animals such as cattle, goats, sheep, and deer naturally acquire B12 from their gut microbes, whereas fish and shellfish get it through biomagnification in the marine food chain. In turn, humans obtain cobalamin by eating animals or seafood.
Strict vegans who avoid animal products can easily become deficient in Vitamin B12, and even non-vegetarians can be deficient. Vitamin B12 deficiency is one of the leading nutritional deficiencies in the world. Symptoms of deficiency are broad and vague, and include fatigue, weakness, memory loss, constipation, and a yellowish skin hue.
In the 1950’s it was discovered that some seaweeds, particularly Asian nori species, contained more vitamin B12 than animal or fish products. The B12 is thought to come from the microbial community associated with the seaweed, and not from the seaweed synthesizing it. This finding was embraced by many in the macrobiotic community and may have led some to eat seaweed for the very first time. However, in the decades since, a series of contradictory studies have clouded the issue. Scientists have discovered cobalamin analogues that appear structurally similar to cobalamin but can’t be used in human metabolism. Further complicating the issue is that older analytical methods relied on microbiological assays that couldn’t reliably differentiate between cobalamin and cobalamin analogues. The debate remains unresolved, but a more sophisticated study in 2000 showed that most of the cobalamin detected in Pyropia (formerly Porphyra) yezoensis was indeed biologically active.
However, to our knowledge no similar studies have been carried out on Porphyra umbilicalis growing in the Atlantic Ocean. Commercial food testing labs don’t use the sophisticated test methods required to differentiate between biologically active cobalamin and its analogues. Although our species of purple laver may in fact contain vitamin B12, we don’t advise relying upon it as the sole dietary source of this essential nutrient. Most nutrition experts also advise against this practice.
Wild Harvest & Processing
Laver was traditionally hand harvested in small amounts for home use. The custom in Wales and Ireland is said to be that it shouldn’t be harvested when there’s an “R” in the month…meaning it’s best harvested May-August. Harvesting is done at low tide by individually hand-cutting each frond. Since purple laver is an annual, it’s not critical to leave the holdfast behind or to rely on regrowth of cut fronds to replenish the beds. However, enough of the bed should be left behind to seed the next generation.
Commercial harvesting is fairly limited. Purple laver is not a ‘commodity seaweed’ like some kelp species, and it commands a relatively small market. As noted earlier, though, it was economically significant in Wales for a period in the eighteen-hundreds, and today some commercial harvesting is still carried out in parts of Wales, Ireland, Portugal, Iceland, and Canada.
However, other nori species such as Pyropia yezoensis and P. tenera are among some of the worlds’ most widely cultivated and eaten seaweeds. Although these species may be wild harvested in the regions where they naturally grow, most of the world’s nori supply is farmed.
There is much interest in developing farming methods for Porphyra umbilicalis. The closely related nori species Pyropia yezoensis and P. tenera are among the most economically important mariculture species in the world, worth well over a billion dollars annually. Kathleen Drew-Baker made this industry possible by elucidating the full life cycle of purple laver, allowing Japanese farmers to reliably seed their nets every season in hatcheries and transplant them at sea. Ironically, her discovery was applied in Japan and not in her native England.
This is because Japanese farmers had already been growing nori for hundreds of years. However, for all of that time they had relied upon wild nori spores to naturally seed onto rows of bamboo poles planted in shallow coastal waters. This method was unreliable and in some years no crop at all appeared. When Drew-Baker published her work in 1949 in the journal Nature, Professor Segawa Sokichi of Japan recognized its significance to the Japanese nori farming industry. Within a few years, Japanese nori hatcheries were seeding nets on an industrial scale and farmers no longer had to rely on the vagaries of mother nature.
Nori seaweed farm on the shore of Mie Prefecture, Japan H. Grobe Wikimedia Commons
Nori was the first seaweed crop to be grown successfully at large scale and it paved the way for mariculture of other seaweed species. Nori is primarily grown in Japan, China, and Korea, but Asian nori farming methods have not yet led to the establishment of a similar industry in Europe or North America for Porphyra umbilicalis. This isn’t for lack of trying, however. Attempts to establish a US nori aquaculture industry using Japanese cultivars started as early as 1980 in Washington State, but opposition from riparian land owners and fishermen made it impossible for potential nori farmers to obtain leases.
In the mid 1990’s, the cultivars and technology developed in Washington State were transferred to Coastal Plantations International of Maine (later incorporated into PhycoGen, Inc.). The first crop in Cobscook Bay failed due to oligotrophic conditions (low available nutrients). In the following growing season, the crop was reared near a floating salmon pen where salmon effluents provided adequate nutrients for growth. This was the first example of open water integrated multitrophic aquaculture (IMTA) in the US. However, PhycoGen ran out of funding before a marketable nori sheet could be consistently and efficiently produced.
Although nori mariculture hasn’t yet become established in North America or Europe, interest remains strong, especially among researchers. Focus has shifted away from using Japanese cultivars because they are non-indigenous and perhaps not as well adapted to local conditions. Researchers are instead trying to develop culture methods for native Atlantic species such as Porphyra umbilicalis. We’re encouraged that the recent enthusiasm for sugar kelp mariculture in Maine and elsewhere in the US could eventually lead to successful laver cultivation.