The default reference for BSBI's list of taxa is Stace's New Flora of the British Isles, 4th edition (2019), along with the partial inclusion of additional infra-specific taxa documented by Sell & Murrell's Flora of Great Britain and Ireland. The database includes many additional alien taxa not covered by either of those references. In a small minority of cases we've chosen to diverge from Stace's treatment, for example recognizing Dactylorhiza viridis rather than Coeloglossum viride.
The list of taxa included in the database can't be regarded as a definitive plant taxon list for the UK, because there is far too much scope for ambiguity over whether a taxon is 'wild'. We inadvertently include many taxa that are probably only ever found cultivated in gardens and inevitably omit some taxa that are established in wild situations. We add new alien taxa to the database frequently, the main criteria for inclusion being that the taxon has been reported to be growing in a wild situation and that the name is validly published and accepted.
There are numerous instances where Stace's treatment is not in line with the internationally accepted taxonomic consensus. The advantage for us of persisting with a standard Flora rather than attempting to follow recent taxonomic changes closely is the pragmatic need to provide field recorders with a reasonably stable and well described set of names to record against.
The current taxon list can be downloaded from the database using a query such as:
https://database.bsbi.org/search.php#retrievesaved=0.nvte3&query=db3a8656d68f3caaa3047d7cb1e69e37
That query excludes synonyms and covers all ranks at genus level and below. There are various additional columns that can be included by setting options when you download. We would suggest the following:
