Perspective on the `coded list of the freshwater algae of the British Islesʹ

The features are described of a coding system developed for taxa of freshwater algae in the British Isles. The full list, which includes more than 5000 taxa, is published elsewhere as a hard copy and in several computer-accessible forms, is a much expanded version of a list of taxa published 20 years previously. Records made using the earlier six-digit system can be updated automatically, providing there has been no change in the taxonomic limits separating taxa. Searches can be made using current names, synonyms or authorities. The new coded list employs eight digits, rather than the six digits used previously. The eight digits are used as follows: two for major taxonomic group; two for genus; three for species; one for infraspecific taxon. An alternative system of coding can be employed for those filamentous genera where it is especially difficult to identify organisms to the specific level. Here the final digit is used for one of nine filament width categories.