Arum
John Grimshaw (Sun, 08 Apr 2007 00:34:56 PDT)

Quite a few mesages have flown through cyberspace since this question was
asked, but it needs an answer.

Are you using your "horticultural group system" like a grex in the

It's probably easiest to copy out the notes in the RHS Plant Finder that
define a group and a grex:

Grex
Within orchids, hybrids of the same parentage, regardless of how alike they
are, are given a grex name. Individuals can be selected, given cultivar
names and propagated vegetatively. For example Pleione Versailles gx
'Bucklebury', where Versailles is the grex name and 'Bucklebury' a selected
cultivar.

Group
This is a collective name for a group of cultivars within a genus with
similar characteristics. The word Group is always included and, where cited
with a cultivar name, it is enclosed in brackets, for example Actaea simplex
(Atropurpurea Group) 'Brunette', where 'Brunette' is a distinct cultivar in
a group of purple-leaved cultivars.
Another example of a Group is Rhododendron polycladum Scintillans Group.
In this case R. scintillans was a species that is now botanically 'sunk'
within R. polycladum, but it is still recognised horticulturally as a Group.
Group names are also used for swarms of hybrids with the same parentage,
for example Rhododendron Polar Bear Group. these were formerly treated as
grex names, a term now used only for orchids. A single clone from the Group
may be given the same cultivar name, for example, Rhododendron 'Polar Bear'.

....................................

In the case of Arum italicum with strongly white-veined leaves, which have
been variously known as 'Marmoratum' (= marbled) or 'Pictum' (= painted),
there is clearly a vast number of seedlings that bear this characteristic.
They can't all be one cultivar, but they certainly share the defining
character of white veins and as such the Group concept is ideal. Since
'Pictum' is an undesirable name because of the existence of the species Arum
pictum, Marmoratum is the preferred epithet and Marmoratum Group would
therefore be most appropriate. Within the Arum italicum Marmoratum Group are
numerous selected cultivars (some of dubious value, mind you!) e.g. 'Winter
Beauty', 'White Winter' and these would be written Arum italicum (Marmoratum
Group) 'White Winter'. Seedlings from the clone 'White Winter' would then
just blend back into the Group, unless one were sufficiently distinct to
warrant a cultivar name.

My reservation about the Group concept is that in (let's call them)
unparticular hands it could be used to make something seem better than it
is, and can conceal a multitude of inferior plants. For example, the Actaea
(formerly Cimicifuga) 'Brunette' example, the seedlings can be only just
brown over green, but still count as Atropurpurea Group. The wise gardener
will always go for a named selection anyway, but the less experienced might
be seduced into getting something inferior that bears an important-sounding
name - 'full of sound and fury, signifying nothing.'

As always, careful definition of the Group, or cultivar's characteristics is
very important.

John Grimshaw

Dr John M. Grimshaw
Sycamore Cottage
Colesbourne
Nr Cheltenham
Gloucestershire GL53 9NP

Tel. 01242 870567

COLESBOURNE PARK OPEN DAYS 2007
Easter Monday 9 April, Arboretum Weekend 15-16 September
Gates open 1pm, last entry 4 pm
website: http://www.colesbournegardens.org.uk/