L. britannicum subsp. celticum is listed in Stace (1997) as endemic to the coast from Anglesey to Westmorland. Because of this it has been considered rare and important, and was a UK Biodiversity Action Plan (BAP) species. The UKBAP has undergone a lengthy review process, the results of which were recently published. One of the changes was the removal of L. britannicum because of a taxonomic review. It's also on the 'waiting list' of the The Vascular Plant Red Data List for Great Britain for the same reason.
The only trouble is, I've been unable to find out what taxonomic changes to Limonium have occurred, as the review doesn't appear to have actually been published yet. Thanks to BioImages I know that it was discussed at a conference, but can't find any actual details. I've checked everywhere I can think of to find evidence of the review, but even the 2007 BSBI plant list shows the Limonium binervosum agg. unchanged.
As a result, this subspecies seems to be in a bit of a limbo at the moment. Presumably the people who made the decision to remove it from the UKBAP know the results of the review, even if it hasn't been published yet. Those of us who are out of the loop will presumably have to wait until then and hope that the uncertainty doesn't influence the level of threat to these plants.
From my point of view it is an even bigger deal, as it affects my 'list of the rarest plants that I've found'! For the moment I will construct it with the existing Limonium taxonomy, as follows:
- Ophrys aveyronensis (limited to one valley in the Causse du Larsac, France).
- Limonium recurvum subsp. pseudotranswallianum (limited to the coast of Co. Claire, Ireland).
- Limonium britannicum subsp. celticum.
- Ophrys aymoninii (limited to the Causse region in France).