The two desmid posters (measuring 58 × 84 cm) of David Williamson’s superb illustrations of these microscopic green algae as described in the second edition of the Freshwater Algal Flora of the British Isles have been updated by David John and Joanna Wilbraham. Identification of these frequently beautiful, sometimes bizarrely shaped, three-dimensional microalgae is based largely on cell shape, size and wall ornamentation. David always intended the posters to be a ready means for identifying the more common desmids in Britain and Ireland without the need to refer to expensive specialist books. The posters are used worldwide as identification aids since most of the 450 desmid species/subspecies illustrated are cosmopolitan.
In this 2024 revision of the poster set taxonomic names have been updated to reflect currently accepted taxonomy and nomenclature. Indicated are the relative sizes of the desmid species and those belonging to the same genus are grouped so as to assist comparison. David’s artistic talent was recognized by the Linnean Society of London when in 2017 he received the prestigious Jill Smythies Award as an outstanding botanical illustrator.