In message , Sacha
writes
Edward Hyams wrote that he had this Berberis here when he owned this place.
I may have tracked a possible source from which to buy it but I'd like to be
certain it's the right thing. I can't get any information on the plant, nor
can I find a picture of it anywhere. Is it one that has changed its name in
the last 40 years? Does anyone grow it or know it? Hyams described it as
rare and unusual but not entirely invisible, surely?!

Hillier's Manual has a short paragraph. The newer 4 volume Bean might
also have something. (The 2nd edn, which is available on the web, was
published before the plant was described.)

It's a plant from Upper Burma (Checklist of the Plants of Myamnar says
Kachin state), and it does seem to be fairly restricted in distribution
- it's absent from the Flora of China, so it would appear not to extend
over the border into Yunnan, and while there isn't a good list of the
Thai flora easily available, nothing comes up when searching in the
Thailand domain.

The citation for the original description is Airy-Shaw, H.K., A new
Berberis from Burma, Kew Bulletin 1930: 208-210. (A German precis on the
web says "Beschreibung von Berberis hypokerina aus dem nordoestlichen
Burma, zu der Sect. Wallichianae gehoerig und naechstverwandt mit der
indischen B. insignis".)

Apart from the 2 (3?) UK suppliers, the plant is grown at the University
of Exeter Streatham campus, Bryans Ground in the Welsh Marches, and
Mount Stewart in Northern Island. Kew have a herbarium specimen, but
it's not one of the ones they've digitised. It does seem to be obscure -
the only location growing it outside the UK that turns up in Google is
San Francisco Botanic Garden.

I've found Frank Kingdom-Ward's description (he introduced it into
cultivation). He writes that, unlike many species, this species is
distinctive, so perhaps it will be possible to confirm the identity of
commercially available plants. See
URL:http://books.google.com/books?id=NZiSH4d05TAC&pg=PA139
--
Stewart Robert Hinsley