Description: Thallus erect, flattened and linear, attached by rhizoidal filaments. To a length of 15 or 25 cms and no more than 4 mm wide, unbranched.

Habitat: Epiphytic in the upper sublittoral and lower littoral in exposed areas.

Distribution: Records from scattered sites around the British Isles but generally south-western. Europe: France, Netherlands, Germany, Denmark, Baltic Sea, Sweden, Norway, Faroes and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts and Virginia. Pacific: U.S.A. Australia and New Zealand.

Similar Species: Petalonia fascia but with broader blades.

Key Identification Features:

• Flat, not twisted blades attached by rhizoids.

Distribution Map from NBN: Petalonia zosterifolia at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Petalonia zosterifolia at iNaturalist World Species Observations database.

WoRMS: Petalonia zosterifolia at World Register of Marine Species.