by Norman Todd April 2003
A basic belief, instilled in every Scot of my generation, was that our race could survive in any clime, in any regime, in any soil. Given the slightest opportunity a Scot would put his roots down anywhere.
The Pontica subsection of the Rhododendron genus is a bit like a Scot. More properly, it should perhaps be phrased the other way round. There are members of the Pontica all over the map. Almost anywhere a rhododendron will grow, Pontica will have a settlement. Such a biogeographically sweeping claim will be instantly challenged by those of different national origins, who will point out that no member of the Pontica is known in that great centre of rhododendron diversity – the Sino-Himalayan region. To this, a Scot would reply that the economic incentive – the promise of a bawbee or two – wasn’t very great in that part of the world in the heyday of migration – and if it had only been known that the Gurkhas of Nepal wore kilts, the Scots would have been over there as fast as they could down a dram – or two.
Why there are no Pontica in these high regions (Ted Irving calls them ‘the regions of extreme relief’) is a complex matter. It is a subject that may be addressed by speakers at our upcoming 2005 convention. Dr. Ben Hall from the University of Washington will be talking about the latest studies of DNA in rhododendrons. The analysis of DNA is proving to be a great new tool in helping to solve the mysteries of plant evolution and distribution.
It is not easy for plebs like me, who think in time intervals of hours, days, years or, at most, generations, to grasp intervals of millions of years. When we think of current and past biogeography we have to make the effort to imagine these huge time spans. Rhododendron fossils date back about 55 million years – to just about the time the dinosaurs became extinct. A lot has happened to our planet in 55 million years. Rhododendrons have mutated, moved around, been sexually promiscuous, flourished and perished. They currently inhabit our globe in about the 1000 different sorts. These, we call species. In the last 200 years – not even a blip in this evolutionary time scale – we humans have been presumptuously monkeying around with these 1000, producing a much larger number of hybrids. These we are now growing with wanton abandon.
About 14 of the 1000 species have been grouped together by our taxonomists to form a subsection of the genus Rhododendron called the Pontica. Of all the subsections this one has the widest geographical distribution – western and eastern North America, northeastern Asia, Asia Minor, Siberia, Japan and Taiwan.
The Pontica subsection takes its name from the species ponticum, a name known to everyone who has ever lived or visited Scotland, England, Ireland or Wales. Once when visiting the latter, I noticed an advertisement in a local paper calling for the application of herbicide to Rhododendron ponticum – a pernicious weed. Ponticum was introduced to the British Isles to provide cover for game birds so that the landed gentry could have better shooting. If the gentry had not cut down all the trees that covered the land there would have been no need to try to recover it. Anyway, the immigrant ponticum was so successful in covering up bare land that eradication has to be practiced once again. Readers who questioned the opening analogy of Scots and ponticum may now be in full agreement with its appropriateness.
The provenance of ponticum is the Caucasus and northern Turkey. David Leach wrote a fascinating article entitled “The Two Thousand Year Curse of the Rhododendron”. One section of this article features ponticum as the villain. In 401 B.C. the Greek military commander Xenophone was retreating from Babylon. Near Trebizond, on the coast of the Black Sea, his pursued army came across “great quantities of beehives.” Xenophone wrote, “All the soldiers who ate of the honeycombs lost their senses, and were seized with vomiting and purging, none of them being able to stand on their legs. Those who ate but a little were like men drunk, and those who ate much, like madmen, and some like dying persons. In this condition great numbers lay on the ground, as if there had been a defeat, and the sorrow was general. The next day, none of them died, but recovered their senses about the same hour they were seized; and the third and fourth day they got up as if they had taken a strong potion.” Fortunately for Xenophone, his pursuers did not find him or his horizontally heaving army and he successfully completed his retreat.
Three hundred and thirty five years later, three Roman armies under Pompey camped at almost the precise spot as Xenophone had. This time the antagonist, the King of Pontus, with his army, massacred the prostrated Romans. Caveat ponticum.
R. ponticum has such a bad reputation that it is seldom planted nowadays apart from the variegated leaf forms which are proving to be quite popular. However, in the Victoria area and elsewhere, ponticum (see below for an alert) is ubiquitous. Most of the rhododendrons imported to this area prior to WWII were grafted plants. The understock was usually ponticum. The reasons for choosing ponticum for understock were its ease of rooting as a cutting and its eagerness to grow from seed. This vigour is such that it has subsequently overwhelmed the desired grafted material and ponticum flourishes with its mauve flowers held just as high as the head of the King of Pontus.
Holding ponticum as the ‘mother of evil plants’ has recently taken a bit of a hit. Perhaps the ‘mother’ connotation may be acceptable but there could also be a ‘father’ involved. David Chamberlain of the Royal Botanic Garden, Edinburgh, gave a talk at the 1999 International Rhododendron Species Symposium in which he cited some studies that had been done by a doctoral student at St. Andrews University in Scotland. It had been long known that plants from the Turkish population of ponticum did not do well in the British Isles. The Turkish ponticum is, in fact, quite a tender plant. How then were the introductions that were made in the 1800’s so successful? These earlier introductions had come from what were thought to be populations of ponticum growing on the Iberian Peninsula that reach as far south as Gibraltar. Comparing the DNA of the British weed plants with the DNA of Turkish plants and with the DNA of other members of the subsection showed that the weeds were hybrids with the paternal DNA coming from R. catawbiense – a native of eastern North America! What was thought to be ponticum was the result of the mating of these two closely related species. R. catawbiense is famous for its gift of extreme hardiness to its hybrids. In the early days of hybridization it, and its close cousin caucasicum, gave rise to a group of hybrids known as ‘The Ironclads’, some of which are still popular today. The addition of catawbiense to ponticum gives an outstanding example of what is known as ‘hybrid vigour’. Caveat ponticum x catawbiense.
The species catawbiense in its more compact forms is a much better garden plant than the heretofore-named ponticum. Two forms are not common in cultivation – catawbiense ‘Album’ and catawbiense ‘Boursault’, the latter having lilac-purple flowers. Some suggest these are hybrids but they still go under the specific name. A plant known as ‘Roseum Elegans’ may also be a form of catawbiense. Joseph Gable of Pennsylvania raised ‘Catalga’ from the seed of the wild white form and it is credited with being the most attractive of all. These plants are particularly useful for having a latish blooming time – late May into June. One of the toughest and easiest to grow of all rhododendrons is ‘Cunningham’s White’. This is a cross between caucasicum and ponticum and is now used extensively as the understock for grafting, particularly in Europe. A plant with ‘Cunningham’s White’ roots is claimed to be more cold hardy, less prone to root rot and have more intense colour in the flower.
In North Carolina the hills are a mass of catawbiense. One writer claims that the catawbiense bloom is the finest floral display in all of North America; the entire vista becoming a billowing ocean of mauve rhododendrons.