Skip to content

Your account

With an account, your progress (modules read, XP, badges, cards, notebook, pack, challenges) follows you on every device. Without one, it stays in this browser.

or
Low toxicity☠️ To avoid

⚠️ Desmarestia (acid kelp)

Desmarestia spp. · Desmarestiaceae

🐚 Coastline
🧠 To remember it“Almost all European seaweeds are safe - except Desmarestia, which you can recognize by its acidity” - the general rule of non-toxic European seaweeds has one clear exception you must know before tasting.
Desmarestia (acid kelp) — Desmarestia spp.

🔍 Identify it without mistakes

Filamentous or finely branched bushy brown alga, often olive-green to brown, distinguished from all other edible seaweeds by a unique chemical defense mechanism: it stores concentrated sulfuric acid in its cells.

  1. highly branched thread-like brown alga (looks like threads or a feather duster depending on the species)
  2. found in the lower intertidal zone, exposed to the air at low tide
  3. on contact with air, releases a strongly acidic liquid that damages the plant itself and neighboring seaweeds
Sizevariable depending on the species, from a few cm to over 1 m
Floweringno flowering (alga)
Habitatrocky intertidal zones worldwide, particularly cold and temperate waters, regularly exposed to air at low tide

⚠️ Not to be confused with

Other edible brown seaweeds harvested in the same basket (-)low for direct ingestion (the very sour taste deters you from eating a dangerous amount), but real during foraging: mixed with other seaweeds in the same container, it can damage or destroy them with its acidity

To tell them apart: unlike all European edible seaweeds which are non-toxic, Desmarestia is recognized by its immediate sour taste and its corrosive effect on neighboring seaweeds in a foraging basket

🍽️ Eating it

Tasteextremely sour, inedible

Preparation : do not consume and especially do not mix it with other seaweeds harvested in the same bag or basket - its intracellular sulfuric acid damages other species upon prolonged contact

💊 Healing with it

aucun

Level of evidence : traditional use — phycological literature (Desmarestia, acid kelp)

⚠️ ingesting large amounts of sulfuric acid can cause severe digestive distress, but the taste is so repulsive that significant accidental ingestion is unlikely; the main risk is contaminating a harvest of edible seaweeds

Sources (1)

No entry replaces a certain identification in the field, or medical advice. When in doubt: don't eat it. If ingestion is suspected: poison control or 112/911.