Clearing up cultivars
YOU keep using it,’ said my visitor, ‘but what does it mean and is it really necessary?’ He was talking about ‘cultivar’. A portmanteau word combining ‘cultivated’ and ‘variety’, it was introduced in 1923 by the American horticultural botanist Liberty Hyde Bailey, who explained: ‘I now propose another name, cultivar, for a botanical variety, or for a race subordinate to species, that has originated and persisted under cultivation.’
Today, we’d depart from Bailey’s definition in certain respects. For example, although most cultivars originate in cultivation, some are discovered in the field. The golden sedge Carex elata Aurea, the bronze-leaved celandine Ranunculus ficaria Brazen Hussy and the corkscrew hazel
Corylus avellana Contorta were chanced-upon in the English countryside. Mutations of familiar species, they were judged horticulturally desirable in their distinctiveness, taken into gardens, propagated and named, so becoming cultivars.
‘Put simply,’ I told my visitor, ‘a cultivar—cv, for short—is a plant variety that is maintained in cultivation and has one or more distinctive features that it retains when propagated. It may begin as a collection from Nature, but more usually it is selected, raised or bred in nurseries and gardens.’ ‘In that case,’ he replied, ‘why not just call them “varieties”? Why the jargon?’ The problem, I explained, is that ‘variety’ or varietas (var.) is a taxonomic term for a wild population of a species that differs in significant ways from the type, as that species’ norm, its original defining state, is called.
To illustrate, I pointed to my winter border and two kinds of wood spurge, Euphorbia amygdaloides; a variable species found wild from the UK to Western Asia. One, with a native distribution limited to Turkey, and consistently tougher, broader and glossier leaves than the type, is a botanical variety, E. amygdaloides var. robbiae. The other, a random variant close to typical European wood spurge, but flushed purple-red and maintained in gardens on account of this unusual colouring, is a cultivar, E. amygdaloides Purpurea. Obviously, it would be wrong to accord these two plants the same status.
Cultivars aren’t so much substantial and abiding variations as sporadic deviations from the norm: growth that’s dwarf or ramrod-straight instead of tall or bushy; leaves that are variegated, lacily cut or densely crisped; flowers that are atypically large, coloured or doublepetalled; fruit that lacks seeds.
As well as mutations such as these, cultivars can arise through hybridisation. To stay with my winter border, Helleborus Pink Frost was selected from among the varied offspring of a garden cross between H. niger and H. lividus, a hybrid known collectively as H. x ballardiae.
The variations enshrined in cultivars might well prove insignificant and ephemeral in the wild. To us, however, they are great, accounting for the majority of ornamental, edible and other economic plants, and so we seek, contrive and perpetuate them. As ancient and widespread as cultivation itself, cultivars are vivid proofs of human inventiveness and husbandry. And yet it was only as recently as 1953 that science set out how to define and name them, in the first edition of the International Code of Nomenclature for Cultivated Plants (ICNCP).
This revolutionary publication was masterminded by a British botanical great, William T. Stearn. At the time, he was employed by the RHS, and the Society has continued to lead in the Code’s development ever since, chiefly through its luminaries Chris Brickell, Alan Leslie and John David.
In addition to assisting the world to name its cultivars, the RHS keeps registers of them, investigating and amassing past records, making sure that the right name is applied to the right plant and the right breeder, and receiving new applications from growers across the globe.
The Society is currently International Cultivar Registration Authority for nine major plant groups, among them, Clematis (with more than 8,000 cultivar names now in the register), Lilium (more than 15,000), Rhododendron (about 34,000), and orchid hybrids (more than 169,000). As well as having immense horticultural value, this service is likely to grow in importance to business as plant-patenting increases. However, even more crucial for me is this: at a time of anxiety about our place in the world, here is something truly global that a British organisation pioneered and still does supremely well.
‘I see,’ said my visitor, ‘handy term, “cultivar”. I’m going to have to get used to it.’
Next week: Pears for heirs
Cultivars are vivid proofs of human inventiveness