In article , papa papanix@removen
ospam.btopenworld.com writes
I have what was labelled as Polygonum bistorta 'Superbum' in my garden.
The RHS does not have it listed but does have Persicaria bistorta
'Superba'. Are they the same thing? What is the correct current
taxonmy of this plant? I assume that somewhere along the line the name
has changed but need to know which is the right name. As the 03/04
Plantfinder has it has P. bistorta 'Superna' that that is the right
name. If so then what happened to Polygonum?


Polygonum has been chopped into pieces (as per Cornus and
Chyrsanthemum). The less drastic version - which appears to be what
PlantFinder is using - has Polygonum, Persicaria and Fallopia (the
latter includes Japanese Knotweed). The more drastic version adds
Aconogonum, Koenigia and Bistorta, and perhaps other genera; in this
versions Polygonum bistorta aka Persicaria bistorta becomes Bistorta
officinalis.

The best reference I could find online was from "Contributions to the
Flora of Hawaii". It reads "The genus Polygonum has presented taxonomic
problems since its establishment by Linnaeus in 1753. In the ensuing
years, several authors have attempted to divide the genus into more
natural units, the most recent being Louis-Philippe Ronse Decraene who
chose to investigate the floral morphology of the genus as a research
topic for his Master of Science degree in plant taxonomy. His data
supports the division of Polygonum into two tribes containing ten
genera, a classification that is gaining wide acceptance."

The family boundaries in that area have also been revised - see the
April 2002 issue of Fremontia for an overview (URL:http://www.cnps.org/
publications/Fremontia_Vol30-No2.pdf)
--
Stewart Robert Hinsley