In article ,
David Hill wrote:

When we grew blackberries as a crop we would always cut out the old
stems after fruiting and tie in the new growth as the new stems gave the
best crop, but here; in South Wales; I find that most blackberry stems
last for 3 or 4 years if not removed, they are wild and I'm not to happy
either,

Interesting. It could be a variant that is widespread in the south
west and rare elsewhere. Several of the variants are local.

Found this interesting Blackberry a few years ago,
http://s240.photobucket.com/albums/f...berryleafx.jpg
A good medium sized fruit, but a stem grew in an unused polly tunnel and
the flavour was great, you wouldn't have known it was a blackberry.

It might be Rubus laciniatus or a hybrid of it. There is also a
R. fruticosus var. laciniata.

Regards,
Nick Maclaren.