GUTWEED GREEN SEAWEED
Gutweed (Ulva intestinalis) is a bright green seaweed that grows in fine tubular fronds, common on shores all around Britain. The name comes from the shape — hollow tubes, often inflated with oxygen, that do look faintly intestinal. It's also one of the seaweeds behind Japanese aonori.
What It Looks Like
Gutweed grows as slender, unbranched green tubes, usually 10–20cm long but sometimes reaching 30cm. The tubes are hollow and often trap bubbles of oxygen produced during photosynthesis, which makes them float upright in rock pools.
It's found high on the shore as well as low, and tolerates brackish water — so it turns up in estuaries and freshwater seeps where most seaweeds won't grow. In summer it can carpet whole stretches of rock in vivid green.
What It Tastes Like
Mild and lightly savoury, with a clean sea flavour rather than a strong one. Raw it's soft and slippery. Dried and fried it turns crisp and nutty, which is how it's most often eaten.
The Aonori Connection
Several Ulva species — including this one — are dried and flaked to make aonori, the green seasoning scattered over okonomiyaki, takoyaki and yakisoba in Japan. A seaweed most British beachgoers walk past is a everyday ingredient elsewhere.
You can make a rough version at home: rinse well, dry thoroughly, then crumble or blitz to flakes.
How to Use It
- Dried and flaked — as a finishing seasoning over rice, noodles, eggs or chips.
- Fried crisp — dried first, then flash-fried in hot oil for a few seconds.
- In soups — added at the end, off the heat, so it keeps its colour.
- Through batters — stirred into tempura or fritter batter for savoury depth.
- Pickled — young tubes hold up well in a light vinegar pickle.
Where It Grows, and Where Not to Pick
Gutweed thrives on high nutrient levels, which means it's most abundant exactly where you shouldn't harvest — near outfalls, run-off and enclosed harbours, where it can form thick green blooms.
A rock heavy with gutweed in still water is a water-quality signal, not an opportunity. Pick from clean, open coast with good tidal movement, and rinse thoroughly.
Harvesting
Cut with scissors and leave the base attached so it regrows. Take from living plants rather than the strandline — gutweed is thin and breaks down fast once detached. Take a small proportion of what's there.
Nutrition
Gutweed contains vitamin C, vitamin K, iron, iodine and dietary fibre. Iodine levels are much lower than in the kelps.
Related
Gutweed sits with the green seaweeds alongside sea lettuce, its close relative. See our guide to edible seaweed in the UK, or the full guide to edible seaweed.
Seaweed has been a source of savoury flavour for centuries. Sozyë's sauces are brewed from a blend of wild Scottish seaweeds, harvested off the north coast of Scotland.