- Kingdom: Plantae
- Phylum: Ochrophyta
- Class: Phaeophyceae
- Order: Laminariales
- Family: Chordaceae
- Scientific name: Chorda filum
- Norwegian: martaum, åletang
This brown seaweed is also known as mermaid's tresses and dead man's rope. As the names indicate, has long unbranched fronds. The fact that they are hollow provide sufficient buoyancy for to stand upright in the water. The diameter is 5mm. They may reach a length of 8-10 meters, but 2-6 is common. The selace typically grow 17 cm each month, but they annuals and die during the winter.
It grows on stones and gravel in the lower tidal, or just below the tidal zone. Sometimes it just floats around in the water. It seems to prefer sheltered or medium exposed locations.
It is widespread on the Northern hemisphere.