BSBINews - BSBI Archive - Botanical Society of the British Isles

Conference Report - 2009 - BSBI Spring Conference on alien trees and shrubs, Berwick 61
New Naturalists book on ancient woodland.
Most surveyors don't have the taxonomic
skills to identify hybrids or infraspecific taxa,
but this is not a reason to ignore them!! We
should arguably just use better surveyors in
order to comply with our international obligations
on conserving biodiversity - there are
plenty of them freelance these days.
The next group mentioned by Clare was
Crataegus monogyna (Hawthorn), with its
four subspecies and three varieties, which all
grow in Cambridgeshire hedges, but only one
of which is native. Again she asked: 'Does it
matter?' , and pointed out that non-native taxa
often flower much earlier than the native, and
wondered if there was an issue relating to the
Woodland Trust's Phenology Network recording
scheme where the first flowering of
hawthorn will have many erroneous records of
the non-native subspecies. A Phenology
Network statistician argued that, due to the
size of the data set for hawthorn (over 100,000
records) any 'bias' caused by recording the
wrong taxon would not influence the outcome.
It was also mentioned that the need for planting
trees and shrubs of local provenance has
become well-known and that most plantings
are of native origin. While the statistical
argument may hold, the latter claim does not.
Nurseries are claiming, usually in good faith,
to supply native plants, but they often are not
- they simply do not have the identification
skills to know otherwise. Clare emphasised
this point by remarking that when she had
tried to get Prunus serotina and P. virginiana
specimens from nurseries, she found them all
labelled P. padus, because, she was told, 'that
is what people want'!
After the Society'S AGM, posing for a group
photograph (see inside Front Cover), and an
excellent buffet lunch, delegates re-assembled
for the afternoon session, chaired by another
vice-president, John Bailey. He introduced
the first speaker, James Cullen, the Director of
the Stanley Smith (UK) Horticultural Trust,
who gave an intriguing talk on the taxonomy
of Rhododendron ponticum (Rhododendron)
as naturalised in Britain.
Rhododendron ponticum is a curiously
unknown plant, considering its widespread
distribution in the British Isles, and recent
genetic analyses have indicated that our taxon
is a mixture of three, maybe four species.
There are over 1000 species of Rhododendron
recognised today, with two main centres of
population in New Guinea and China. Rhododendron
taxa can be split into two main groups
based on the presence or absence of tiny scales
on the underside of the leaves, and while
'scaly' taxa can hybridise freely with other
'scaly' taxa, and 'non-scaly' with 'non-scaly',
producing hybrids with great hybrid vigour, it
is very difficult to get hybrids between the two
groups.
Rhododendron ponticum is a rather uniform
'non-scaly' species, with leaves completely
hairless beneath. British material is very
vigorous and, unlike true Rhododendron
ponticum, all British material comes from the
Iberian peninsula, with slightly hairy (not
hairless) ovaries.
The British taxon is a hybrid produced in the
second half of the 19 th Century by crossing
R. ponticum with R. catawbiense, R. maximum
and possibly R. macrophyllum, then backcrossing
the resultant progeny with the parents
and growing all of them side by side in plots,
allowing cross-pollination to occur. This
produced a whole range of hybrids with
various characteristics, and it is now impossible
to segregate any taxa within this 'ponticum
soup'. This was the result of nurserymen
wanting a hardy version of R. ponticum. This
ponticum hybrid was also used as rootstock for
better and more desirable taxa as they were
introduced from abroad, and the rootstock
often outlived the graft taxon and can still be
seen today. Rhododendron was also found to
be very good for pheasant cover and was
widely planted for that purpose.
The British hybrid, soon to be given a new
name, is very difficult to eradicate and
involves cutting back the parts above ground,
three years of ploughing and the application of
very nasty chemicals. The moral of this tale is
not to indulge in genetic manipUlation - you
might create a monster!
The next speaker, former BSBI Coordinator
Cameron Crook, gave a masterful introduction
to the identification of conifers in Britain. He