section_path: Numbers
section_name: Numbers
paragraph_text: Numbers
  
  The Algal Collection of the US National Herbarium (located in the National Museum of Natural History) consists of approximately 320,500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species (that number remains unknown). Estimates vary widely. For example, according to one standard textbook, in the British Isles the UK Biodiversity Steering Group Report estimated there to be 20,000 algal species in the UK. Another checklist reports only about 5,000 species. Regarding the difference of about 15,000 species, the text concludes: "It will require many detailed field surveys before it is possible to provide a reliable estimate of the total number of species..."
  
  Regional and group estimates have been made, as well:
  
  and so on, but lacking any scientific basis or reliable sources, these numbers have no more credibility than the British ones mentioned above. Most estimates also omit microscopic algae, such as phytoplankton.
  
  The most recent estimate suggests 72,500 algal species worldwide.