Important Plant Areas for algae - Natural History Museum

3.2 UK ALGAL DIVERSITY
Hardy & Guiry (2003) recorded 692 species in The Atlas of Marine Algae of Britain and Ireland (6 only
known from Ireland), which represents approximately 14% of the world’s known marine algae. The
number of species mentioned in The Freshwater Algal Flora of the British Isles (John et al., 2002) is
about 5,000 and these are listed in A Coded List of British Freshwater Algae (Whitton et al., 2003). The
number of seaweeds is almost certainly a more accurate figure since most microscopic algae are poorly
known. A comparison of the number of species in the groups covered in this document is given in Box
4.
BOX 4
Species Diversity in the UK
Numbers for marine algae refer only to ‘seaweeds’ (benthic macroalgae) growing in brackish water
and/or under fully marine conditions. These are compared to the numbers of freshwater species that
occur in each of these phyla. For the species diversity of other freshwater phyla in the UK, see John et
al. (2002).
Freshwater
Marine
Rhodophyta (red algae) 22 339
Phaeophyceae (brown algae) 2 185
Chlorophyta (green algae) c. 1000* 100
Xanthophyta/Tribophyta (Yellow-green algae) 73 16
*includes 30 stoneworts and over 800 desmids
3.3 ALGAL HABITATS AND THEIR CLASSIFICATION
Algae occur not only in a wide range of aquatic habitats but are also common in terrestrial habitats
including soil and soil-free surfaces. Little is known of the status of terrestrial algae or freshwater and
marine algae in many of those habitats recognised in the European Union Nature Information System
(EUNIS) classification of habitat types. (For the most important habitats for the algae under EUNIS, see
Box 5.)
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