Biodiversity & Conservation

Sea oak - Halidrys siliquosa - General information

Halidrys siliquosa

Image Steve Knight - Halidrys siliquosa in rock pool. Image width ca 1m.
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Distribution map

Halidrys siliquosa recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

Sightings Have you seen Halidrys siliquosa?
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Halidrys siliquosa is not listed under any importance categories.

General information

Key Icon Researched by: Dr Harvey Tyler-Walters and Paolo Pizzolla Text page icon Refereed by: Dr Stefan Kraan

Taxonomy icon Taxonomy

Phylum Ochrophyta Brown and yellow-green seaweeds
Class Phaeophyceae
Map icon Recorded distribution in Britain and Ireland Widely distributed and fairly common in the Britain and Ireland.
Habitat information icon Habitat information A distinctive and common rock pool seaweed from the middle to lower shore (may be found in upper eulittoral but only in rock pools). It may also form a zone in the sublittoral below the lower limit of Laminaria digitata. It often supports a range of invertebrate epifauna such as bryozoans, hydroids and ascidians and epiflora such as small red algae, Ulva sp. and other fucoids.
Text page icon Description A large sturdy brown alga 0.3 -1 m in length (occasionally up to 2 m) rising from a strong, flattened cone shaped holdfast. The main stem is flattened and branches alternately to give a distinctly zigzag appearance. The stem bears a few, flattened ribbon-like 'leafy' fronds. The ends of some branches bear characteristic pod-shaped air bladders (about 0.5 cm wide by 1-4 cm long) that are divided by transverse septa into 10 or 12 compartments. The branches also bear reproductive bodies that appear similar to the bladders but lack the septa. Young plants are olive-green in colour while older specimens are dark brown and leathery. This species is perennial.

This review can be cited as follows:

Dr Harvey Tyler-Walters and Paolo Pizzolla 2008. Halidrys siliquosa. Sea oak. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 11/02/2012]. Available from: <http://www.marlin.ac.uk/speciesfullreview.php?speciesID=3447>