The first edition (2011) of Atlas of British and Irish Hawkweeds was based on David McCosh's database of c.19,000 Hieracium and Pilosella records, representing over 420 species as defined in Peter Sell and Gina Murrell's Flora of Great Britain and Ireland (2006). Since this edition, various changes have been made to the Hieracium flora of Britain and Ireland. Eleven species have been added to the list and a further eleven, formerly thought to be the same as related Scandinavian species, have been renamed. The names previously used for these species have been included as synonyms in this new edition.
As in the first edition, each species account has Latin and English names, distribution map at hectad resolution (pre and post 1960 records are indicated by different symbols), representative silhouette, brief notes, list of vice-counties from which it has been recorded, and IUCN threat category. There is also a list of species accepted for each vice-county. The new edition has been formatted in a larger size than the original edition making the maps easier to read.
This second edition incorporates a significant number of records from field work and from additional herbaria. The bibliography gives publication details for the new or renamed species. Plants that with present taxonomic knowledge cannot be ascribed to species and share the characteristics of a basal rosette, cauline leaves 0-1(2), phyllaries with numerous to dense glandular hairs and without simple hairs are referred to informally as H.exotericum agg. No attempt has been made to map such plants, which are widespread. Hieracium species thought to no longer occur (extinct native or introduced species with no recent records) are relegated to Appendix 1, together with plants of uncertain occurrence. Appendix 2 is a new addition, with images of selected leaves of all species with blotched or spotted leaves, as this can be a short-cut to identification. Sell & Murrell's (2006) numbering has been retained for ease of cross-referencing, adding a letter for additional species, usually at the end of the relevant section (e.g. 46a Hieracium jonesianum).