Black siphon weed (Vertebrata fucoides)

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



A leathery, tufted red seaweed that is brownish red, dark purple or black in colour but that can be bleached to brown in summer. The distinct thallus grows to 3-30 cm in height consisting of dense cylindrical to irregularly rounded tuffs of black leathery fronds. It has many branches with a highly variable pattern from an irregular spiral to a regular feather arrangement with branchlets arranged alternatively in two rows either side. The base of the plant remains free of branches and is tough and flexible in texture. 

Recorded distribution in Britain and Ireland

Widely distributed and common in Britain and Ireland.

Global distribution

Widely distributed in the Baltic Sea and the northwest of Europe from Germany to Portugal. Recorded from Newfoundland to North Carolina, Iceland, the Black Sea and the east coast of Argentina and Uruguay.


It is found in abundance on a wide variety of substrata from maerl beds to pebbles and bedrock to artificial substrata such as marina pontoons. It is found in extremely sheltered to extremely wave exposed sites and sub-tidally at sheltered sites with some current exposure. It is tolerant of sand cover and high levels of silt.  It is a dominant intertidal species in some areas.

Depth range

Mid intertidal to 20 m

Identifying features

  • Dark brownish-red, brownish-purple or black in colour, bleaching to light brown. 
  • Thallus denuded at the base.
  • Much branched laterals in an irregular to regular feather like pattern. 
  • Grows to 3-30 cm in height. 
  • Cortication ranges from dense to absent. 

Additional information

This species was accidentally introduced into the Mediterranean on multiple occasions most likely by fishing baits and shipping. First found in the Étang du Prévost (France) in 1988 it is now widely distributed throughout the Mediterranean (Guiry & Guiry, 2022).

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

  3. Maggs, C.A. & Hommersand, M.H., 1993. Seaweeds of the British Isles: Volume 1 Rhodophycota Part 3A Ceramiales. London: Natural History Museum, Her Majesty's Stationary Office.


  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: 2024-06-15


This review can be cited as:

Mardle, M.J., 2022. Vertebrata fucoides Black siphon weed. 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 15-06-2024]. Available from:

Last Updated: 19/01/2022