Biodiversity & Conservation

A red seaweed - Polyides rotundus

Polyides rotundus

Image Jason Hall-Spencer - Polyides rotundus. Image width ca 7 cm.
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Distribution map

Polyides rotundus recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

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Polyides rotundus is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Rhodophyta Red seaweeds
Class Florideophyceae
Authority (Hudson) Greville (1830)
Recent synonyms Polyides caprinus
Map icon Recorded Distribution in Britain and Ireland Occurs around all coasts of Britain and Ireland. There is a paucity of records from south east England which may reflect a lack of suitable substrata.
Habitat information icon Habitat information Grows attached to rock and stones in pools in the lower intertidal and subtidally to 20 m. The holdfast is often buried by coarse, sandy deposits.
Text page icon Description A dark red or blackish seaweed with smooth, cartilaginous, cylindrical fronds, branching dichotomously in roughly the same plane. The fronds rise from a fleshy, discoid holdfast up to 2 cm in diameter. The reproductive bodies occur as oval shaped swellings along the sides of the branches or occasionally encircling them. The seaweed grows up to 20 cm in length.
Identifying features
  • erect, cylindrical, dichotomously branching fronds.
  • fleshy, discoid holdfast.
  • dull red in colour, blackish when dry.
  • tetrasporangia cruciate or irregular, borne on uppermost branches which become slightly thickened.
  • cystocarps produced in oval, spongy, wart-like growths on one side of, or encircling, branch.
  • spermatangia thin, plate-like and colourless.
Additional information icon Additional information

This review can be cited as follows:

Will Rayment 2003. Polyides rotundus. A red seaweed. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 03/09/2010]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=4168>