Sea fern weed (Halopteris filicina)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help



Halopteris filicina is a greenish-brown, fern-like seaweed that grows up to 10 cm in height. A number of individual stems, that are elongate and pointed towards the tip, grow from a holdfast that has a root-like appearance. Each stem bears alternately-placed side branches that, in turn, each bear short, pinnate branchlets. The density of these branches increases towards the upper part of the stem. Reproductive sporangia are ovoid in shape and positioned singularly at the axis of branchlets on short stalks.

Recorded distribution in Britain and Ireland

Halopteris filicina is widely distributed on southern and western coasts of Britain and Ireland.

Global distribution

Halopteris filicina is usually found in the Mediterranean and warm seas of the northern hemisphere.


Halopteris filicina inhabits the lower shore and shallow water growing attached to rock, shells and large seaweeds.

Depth range


Identifying features

  • Greenish-brown fern-like seaweed.
  • Up to 10 cm in height.
  • Individual stems bear alternate pinnate branches.
  • Holdfast root-like in appearance.
  • Ovoid-shaped sporangia on short stalks in branch axis.

Additional information

Halopteris filicina is similar to Halopteris scoparia but is less bushy in appearance.

Listed by

- none -


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  8. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin.


  1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset accessed via on 2018-09-25.

  2. Fenwick, 2018. Aphotomarine. Occurrence dataset Accessed via on 2018-10-01

  3. Manx Biological Recording Partnership, 2017. Isle of Man wildlife records from 01/01/2000 to 13/02/2017. Occurrence dataset: accessed via on 2018-10-01.

  4. National Trust, 2017. National Trust Species Records. Occurrence dataset: accessed via on 2018-10-01.

  5. NBN (National Biodiversity Network) Atlas. Available from:

  6. OBIS (Ocean Biodiversity Information System),  2023. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2023-12-11


This review can be cited as:

Richards, S. 2007. Halopteris filicina Sea fern weed. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 11-12-2023]. Available from:

Last Updated: 12/09/2007