Velvet horn (Codium tomentosum)

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



A small green alga (up to 30 cm long) with a dichotomously branched, cylindrical frond. The frond is solid and spongy with a felt-like touch and has many colourless hairs which can be seen when the plant is immersed in water. The holdfast is disc-like and formed from many fine threads.

Recorded distribution in Britain and Ireland

Codium tomentosum occurs mainly in the south west of the UK and is becoming quite rare. Both pollution and competition with Codium fragile have been suggested as potential causes of its decline.

Global distribution



It attaches to exposed rocks and occurs in rock pools on the lower shore.

Depth range


Identifying features

  • Small green seaweed, up to 30 cm long.
  • Dichotomously branching with a cylindrical frond.
  • Felt-like to the touch.
  • Disc like holdfast made from fine threads.

    Additional information

    Codium tomentosum can be confused with Codium fragile. However, Codium tomentosum tends to have a more slender frond with rounded tips whereas Codium fragile has pointed tips to the frond.

    Listed by

    - none -


    1. Burrows, E.M., 1991. Seaweeds of the British Isles. Volume 2. Chlorophyta. London: British Museum (Natural History).

    2. Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.

    3. Hayward, P., Nelson-Smith, T. & Shields, C. 1996. Collins pocket guide. Sea shore of Britain and northern Europe. London: HarperCollins.

    4. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

    5. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

    6. Trowbridge, C.D., 1998. Ecology of the green macroalga Codium fragile (Suringar) Hariot 1889: invasive or non-invasive subspecies. Oceanography and Marine Biology: an Annual Review, 36, 1-64.


    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. Manx Biological Recording Partnership, 2018. Isle of Man historical wildlife records 1995 to 1999. Occurrence dataset: accessed via on 2018-10-01.

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

    6. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-07-14

    7. Royal Botanic Garden Edinburgh, 2018. Royal Botanic Garden Edinburgh Herbarium (E). Occurrence dataset: accessed via on 2018-10-02.


    This review can be cited as:

    Pizzolla, P.F 2007. Codium tomentosum Velvet horn. 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 14-07-2024]. Available from:

    Last Updated: 13/08/2007