OK, I have made all the changes that I think are necessary. There are others that could be made, to account for Stace3, but I will wait on the BSBI treatment of Stace in their list rather than add extra potentially confusing synonyms.
The summary is that we only have one taxon in the UK - L. grandiflora subsp. hexapetala - we do not have the nominate subspecies. Ludwigia uruguayensis & L. peploides are both 'auct. Brit.' junior synonyms of L. grandiflora hexapetala so I have dropped them under L-g-h but I have chosen not to add 'auct.' to their attributes because these names are used in the Wildlife & Countryside Act and cannot be altered in this context. L. hexapetala is another 'auct.' because it is a valid name but not in the context of the UK flora. It was brought in with Stace 3 and will probably be added - as would L. grandiflora 'auct.' but I will let the BSBI rule on how they would like it to finally be arranged.
So, in summary the changes are:
added "Ludwigia grandiflora subsp. hexapetala (Hook. & Arn.) G.L. Nesom & Kartesz"
tvk NHMSYS0020979164
synonymised Ludwigia peploides (Kunth) Raven NHMSYS0020744905
synonymised Ludwigia uruguayensis (Camb.) Hara NHMSYS0020744911
synonymised Uruguayan Hampshire-purslane
potentially (for the future):
add synonym Ludwigia grandiflora auct.
add synonym Ludwigia hexapetala (Hook. & Arn.) Zardini, H. Gu & P.H. Raven +auct. Brit. (Stace3)
I hope that has simplified the situation adequately and it gives everyone the names they need. If for any reason you need to see "L. hexapetala auct." as a synonym then let me know and I will add it :)
Best wishes,
Chris R.
Chris Raper, Manager of the UK Species Inventory, Angela Marmont Centre for UK Biodiversity,
Natural History Museum, Cromwell Road, London, SW7 5BD. (tel: 020 7942 5894)
also Tachinid Recording Scheme (http://tachinidae.org.uk/)