An encrusting red seaweed (Hildenbrandia rubra)

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



An encrusting seaweed that is rose-red, dark-red or red-brown in colour with no surface markings.  The thin thallus (0.2-0.5 mm thick) forms an extensive crust with an irregular outline on the surface of rocks, stones and pebbles.  In some areas, crusts can be as large as 15 cm across.  

Recorded distribution in Britain and Ireland

Widely distributed and common throughout the rocky shores in Britain and Ireland.

Global distribution

Cosmopolitan with a wide distribution throughout north-west Europe.


Found on rocks, stones and pebbles at all tidal levels of the shore. Particularly abundant in moist, shaded areas and the upper shore due to its tolerance of temperature, light and salinity. It is also the only red crust found on rock in the upper shore.

Depth range

Upper to lower shore

Identifying features

  • Thin, unmarked encrusting layer 0.2-0.5 mm thick.
  • Colour varies from rose red to dark red.  
  • Dull when dry. 
  • Irregular outline.
  • No rhizoids.
  • Non-calcareous.

Additional information

The accurate identification of different species of dark encrusting seaweeds requires sectioning and microscopic examination. It can be confused with Hildenbrandia crouaniorum, which is found in similar locations. However, they can sometimes be distinguished by colour as Hildenbrandia crouaniorum normally has a more brownish red colour than Hildenbrandia rubra, which is a brighter rose-red colour.

Listed by

- none -


  1. Bunker, F.StD.P., Brodie, J.A., Maggs, C.A. & Bunker, A.R., 2017. Seasearch Guide to Seaweeds of Britain and Ireland (Second edition). Plymouth: Wild Nature Press.

  2. Fish, J,D., Fish, S., 2011. A Students Guide to the Seashore (Third edition). Cambridge: University press.

  3. Guiry, M.D. & Guiry, G.M. 2015. AlgaeBase [Online], National University of Ireland, Galway [cited 30/6/2015]. Available from:

  4. Hiscock, S., 1986b. A field key to the British Red Seaweeds. Taunton: Field Studies Council. [Occasional Publication No.13]


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

  2. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-05-21


This review can be cited as:

Mardle, M.J., 2022. Hildenbrandia rubra An encrusting red seaweed. In Tyler-Walters H. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 21-05-2024]. Available from:

Last Updated: 14/01/2022