Harvest of the ocean: Weird and wonderful seaside vegetables are making waves in all the best kitchens

Shakespeare gave it a name-check, Charles and Di enjoyed it at their wedding breakfast and fishmongers of old used to tuck it as a freebie into the bags of housewives, who often threw it out as an unwanted weed. Then modern British chefs got hold of samphire, that delicious crunchy, salty native marsh grass which is such a spectacular accompaniment to fish. And now the nation is mad for it.

In past years, addicts have had to pick their own or seek out a trendy fishmonger to sell them a bunch of the stuff when June comes around – samphire's days as a give-away are long over. But finally it has hit the supermarket.

Samphire, along with the less well-known sea aster, has landed at every Waitrose with a fish counter, at £1.99 for 90g. Hard on its heels in some Waitrose stores will be the frankly obscure okahijiki (pronounce it O-ka-ji-ki), a succulent Japanese land seaweed, now being homegrown.You can also buy samphire in M&S.

Meanwhile, the chefs who first popularised shoreline bounty are exploring the possibilities of sea purslane, sea beet, sea kale and sea buckthorn, which along with many varieties of seaweed are on the menu at some of the smartest addresses. "We've been using all this stuff since we opened," says Brett Graham of The Ledbury, the Notting Hill restaurant which made a spectacular leap into the list of the world's best 50 restaurants this year. "I love using seaweed instead of salt as seasoning, while sea vegetables are such a delicate enhancement to fish. We get sea purslane, which I use a lot, and sea aster from foragers. We buy sea lettuce and dulse [a type of algae] ready-salted, and our bladderwrack direct from the fishermen in Cornwall."

He also has such an affinity for monksbeard, a relative of chicory, he brings it in from France, but given the abundance of British marshland, most shoreline produce constitutes a right-on, low-carbon-footprint addition to the vegetable basket.

While samphire consumption is a centuries-old tradition, sea aster – a marine version of the Michaelmas daisy – was introduced to the table barely five years ago by Miles Irving, author of The Forager Handbook. His own interest was piqued by a 1995 Food and Agriculture Commission document exploring the cropping viability of this plant, which grows in most places where samphire thrives.

He now sells it to chef (and Independent writer) Mark Hix and many other restaurateurs, and Waitrose produce buyer Rhonwen Cunningham is counting on Brits cooking it up by the bunch: "We were shown it by the growers we get our samphire from, and thought that looking rather like spinach, it would not be too frighteningly unfamiliar a concept. It's more robust than spinach, but it has this creamy, salty quality which goes surprisingly well with lamb as well as fish." As for the okahijiki, it's what the store settled for after attempting to source an accessible seaweed. "It's known in Japan as 'land seaweed', and is used there as a staple."

While the stems of samphire themselves look like seaweed and taste as we imagine it might – its crunch and salty bite evoke the very essence of the ocean – its origins can be an illusion. Found around tidal rivers – there are beds in East Anglia, Kent, near Southport in the north-west and in Cornwall (where some of the supply has been contaminated by proximity to mines) – the Waitrose supply is being grown under glass in the Midlands.

The reason for forcing up a marsh plant in industrial greenhouses far from the sea? "We simply could not keep up with demand last year," explains Cunningham. "The fish-buying team were begging us to pursue a consistent source, and when we saw it being featured on TV cookery shows and turning up in so many restaurants and pubs, we realised we were on to a big trend and needed to find a dedicated supply."

Sales, in a market which competitors have so far declined to enter, are bullish: "We are already selling 7,000 packs a week in the short time since we have introduced it, and expect to sell at least four times what we did last year," says Cunningham.

Don't think of growing your own, however, warns Sean O'Neill, who raises sea kale and oyster leaf on his Cornish farm for restaurants: "Samphire seed is extremely difficult to get hold of, although the plant grows abundantly in the wild between now and September."

Jeremy Lee of the Blueprint Café, in London, starts begging his fish supplier and foraging friends for samphire as soon as the new year's green shoots start to appear: "It has a great affinity with the spring harvests of peas and asparagus, and we plough through heaps of the lovely stuff," he sighs. "It's available from abroad, but rarely does what is available from other countries capture the magic of the crop from our own extraordinary coastline."

And there's the rub – samphire raised by supermarkets miles from the sea seems destined to make commonplace a vegetable we have come to consider a rare, seasonal and highly prized treat. That seems slightly wrong, like picking up packs of Peruvian asparagus in February instead of waiting for the few precious weeks of more delectable homegrown. On the other hand, creamy, salty sea aster is such a new and fresh taste, a delightful accompaniment to roast lamb as well as fish, that many foodies will forgive it for coming from the landlocked Midlands rather than Morecambe, Mersea or the mudflats of Kent.

And the good news is that a vastly expanded natural supply may soon be on the way: "There is a lot of scope for creating extra saltmarsh where new sea wall is not being erected, which makes this category of produce a profoundly green product," says Irving.

Strangers on the shore

Less common "sea vegetables" – actually, shoreline plants – which are finding their ways into chefs' kitchens include:

Sea purslane – a salty leaf that must be picked off a woody stem, it can be found almost year-round in salt marshes.

Sea kale – growing on shingle, is prized for its beautiful tender, purple leaves.

Sea beet – a beach plant of the chard family, only its rich-tasting leaves are used.

Oyster leaf – too rare to be foraged on a commercial scale, this actually tastes like oysters.

Sea buckthorn - shrub with bright orange fruit which lends itself to desserts and is also sold as juice; the season runs from August to February.

All of the above, except oyster leaf, are available from www.forager.org.uk, which also offers instruction to would-be gatherers.

How chefs are using samphire

Jeremy Lee of the Blueprint Café pairs samphire with clams, with squid in a salad and makes a soup of it with peas and lettuce. "Samphire does not yield easily to inventiveness," he believes. "It remains happiest lightly boiled or steamed and lightly buttered, with a pinch of pepper to add a little mystery."

At the Boundary restaurant samphire appears as a side dish, tossed with lightly sautéed cucumber, as well as paired classically with scallops and baby leeks.

At Scott's, head chef Dave McCarthy bases a risotto on samphire and girolles.

Chefs with an affinity for lamb are also tempted by samphire. Richard Corrigan makes a bold dish of lamb sweetbreads and lambs' liver, pan fried and served with poached samphire and spring onions pickled in vinegar, sugar and mustard seeds.

Brett Graham sometimes pickles samphire itself lightly in two parts apple juice to one part cider vinegar. He likes the way the vegetable works with caramelised fennel to enhance fish.

Cooking with seaweed

These are true sea vegetables; the Japanese have a passion for them, the French and Irish harvest theirs commercially, but in Britain we are only just discovering the culinary delights of kelp and its relatives.

Yoshinori Ishii, executive chef of Umu, finds kombu – Japanese sea kelp – "vital to my cooking. It's thick and tough, so needs to be boiled and reduced; at home I braise it with soy sauce, sake and mirin and eat it with plain rice." Wakame, on the other hand, "has a subtle, sweet flavour and a soft texture; in Japan we eat it in miso soup and salads".

In Britain, sea lettuce is a variety which does not require processing and can be eaten raw as well as lightly poached.

Brett Graham of The Ledbury likes to make a consommé of dried bladderwrack, and also deconstructs nori, the dried seaweed sold in sheets for wrapping sushi. "Once it's mushy, I like to blend it into stoneground mustard."

At The Greenhouse, Antonin Bonnet makes bladderwrack butter to serve with roasted John Dory and caramelised fennel. He also blends kombu broth with wild herbs and grapeseed oil into an "intensely flavoured" dressing for asparagus.

Beachcombers tempted to scoop up bladderwrack and bring it home to the pot should be warned: "It has a much better, more intense flavour when dried," says Graham, who likes to dress roast cod with seaweed butter. And it can be unforgiving. Bonnet warns: "If you leave kombu to infuse for too long, it can release bitter, unpleasant flavours, so you have to be very precise when cooking with it."

Health food company Clearspring market many kinds of dried seaweed, rich in vitamins and minerals, ready to crumble into food.