Proceedings of The Hardy Plant Society's Variegated Plant Study Day, 27-Sep-97
Organized by the Berkshire Group and Variegated Plant Group of the HPS
What a day!
Over eighty people from seventeen counties and as far as Japan found their way to the excellent facilities of the Berkshire College of Agriculture at Hall Place, Burchetts Green near Maidenhead. The friendly and well organized mood was immediately apparent as cheerful guides showed the way from car park to registration desk, where everyone received a raffle ticket with a guarantee of a win. Eager Berkshire members had mustered a veritable nursery of self-propagated plants in carrier bags numbered to match all the raffle tickets. What a good idea; what a good start! Inside there were more plants for sale courtesy of two growers: Monksilver Nursery and Cotswold Garden Flowers. Tables and floorspace were crammed with fascinating displays, and flower arrangements, inside and out, from about thirty members. Posters filled other space… Even if there had been nobody to talk to, there was plenty of interest in all this variegated, and some unvariegated, greenery. But chatter was everywhere. Folks were busying around like bees in a hive, though pausing now and then to partake of the excellent refreshments and cakes, largely the product of yet more effort from the many workers.
10.30am. Informality was suspended as chairs were taken for Beryl Levett's welcome speech, then very soon she introduced us to our first speaker, Ken Burras.
KEN BURRAS - THE NATURE OF PLANT VARIEGATION
After early days in horticulture at Ambleside in The Lake District and Bodnant Gardens in Wales, Ken passed though Kew as a student in the 1950's, before working under Professor C. D. Darlington at the start of 35 years in Oxford Botanic Garden. He was superintendent there for 25 years, and it was there that his curiosity in variegated plants germinated and flourished. The collection of variegated plants were initially rather haphazardly planted, but as Ken started to classify them in terms of variegation, expanding the collection all the while, they were replanted in a more systematic way. At its peak, the collection numbered about 400 types.
As well as being on two RHS committees and working as a horticultural consultant, Ken's interest in variegated plants continues, and has borne fruit in numerous ways, including his 'Streaks and sectors' article in 'The Garden' magazine of the RHS, January 1997 pp.12-15, and his lecture to us today.
Ken set out to show how the different types of variegation had corresponding structural causes, some permanent and inheritable through seed and others more volatile, and based on this categorization, he explained the details using some fine photographs.
Just below the surface of a leaf there may be blisters, which give rise to silvery patches due to light reflecting from the membranes of transparent cells or air pockets. In Pilea cadierei, the aluminium plant, and Pulmonaria this occurs between veins, but in Silybum marianum, the milk thistle, which may be found as escapes along some Sussex roads, it is along veins; and in Cyclamen hederifolium the blisters provide a multitude of variations. To produce these blisters is a natural part of the plants' genetics, and hence such plants come true from seed.
PATTERN-GENE, PIGMENTED, or NATURAL VARIEGATION
Where a plant's genes include instructions for building leaves with multiple pigments, all manner of patterns may result, and these will be permanent features, inheritable through seed. This is the same principle which causes successive generations of butterflies, for example, to have the same patterning. Examples include Euphorbia marginata with its white-edged bracts, the red and green fish-bone pattern of some Maranta; and the iron cross begonia, Begonia masoniana. The Begonia shows nicely how permanent its variegation is, in that adventitious shoots from leaf cuttings give rise to the same leaf patterning as the parent, whether they arise from light or dark areas of leaf. Although most of these plants will produce seedlings similar to their parents, those which are the result of selective breeding, such as Solenostemon (Coleus) blumei, the flame nettle, in all its rainbow variations, will be more unpredictable.
Actinidia kolomikta, with its white-tipped leaves due to pattern-gene variegation, also demonstrates developmental variegation through becoming progressively more pink as the season progresses, the pink simply being more obvious where developed on the white parts of the leaves. Again, such traits are inheritable through seed.
Examples include the marginal chlorosis which can develop in Cotoneaster due to boron deficiency, and interveinal chlorosis in many plants due to magnesium deficiency (which can be rectified in later-formed leaves by watering with Epsom salts).
This has been responsible for giving variegated plants a bad name, though true aficionados will naturally shun such cursory criticism. It is true that some viruses can be debilitating and can spread to many types of plant, but many others are relatively benign and restricted. The mosaic virus which gives Abutilon x milleri and others of the same genus their familiar patterning [which I find very reminiscent of an aerial photograph of a landscape of fields and hedgerows], is largely confined to abutilon (and cotton) plants. It causes partial breakdown of chlorophyll, giving rise to the various colours from green to yellow. In contrast, forms of Vinca major and Ajuga reptans, and possibly even the pretty Pelargonium peltatum 'Sussex Lace' (='Crocodile') get their reticulated (netted) leaf patterning by virtue of a vein-clearing virus. Interestingly, such viruses can be spread to plain forms of susceptible plants by rubbing the leaves lightly between carborundum-dusted finger and thumb. No - sit down - you can try it later!
If genes mutate spontaneously in ways affecting pigmentation, the resulting pattern of variegation depends on where and when the mutations occur: if at the growing point, plain white leaves or shoots may result; if at the leaves, it may cause speckling , spotting, or streaking. Acer pseudoplatanus 'Leopoldii' and Tropaeolum majus 'Alaska' are examples. Such plants usually breed true from seed if they are self-pollinated.
[ Most variegated plants fall into this category, so, although this section is a little complex, stick with me! ]
The preceding mutating variegation involves genes switching on and off at random continuously as the plant grows. However, a one-off mutation affecting the production of green pigment in a growing point can be perpetuated by normal cell division without any further mutations, forming a cell lineage. Such an aberrant cell lineage, mixed with normal cells, may become evident as one of several patterns collectively known as chimeral variegation, the chimera being the mythical Greek creature with a lion's head, goat's body and serpent's tail. Chimeral variegations tend to fall into two groups, either sectorial or periclinal, depending on the way the normal and aberrant cell lineages sort themselves out.
Consider the growing point and stem when cut across and when viewed lengthways. A sectorial chimera has aberrant white cells in divisions arranged like pieces of a cut cake - sectors. These form one or more stripes when viewed along the stem, like stripes in toothpaste, and give rise to corresponding white, green or striped leaves. A periclinal chimera has the aberrant and normal cells in usually three concentric circles. like the structure of a pencil - graphite, wood, paint. This may not be apparent on the outside of the stem, but it becomes more obvious and interesting on the leaves. Peri- means 'around', as in peripheral.
Sectorial chimeras are often unstable, white cell lineages either being outgrown by green ones, or if they manage to produce a wholly white shoot, it will eventually die due to lack of chlorophyll. The stripy-leaved forms of the familiar Tradescantia and the dwarf bamboo Arundinaria auricoma, however, are examples of relatively stable sectorial chimeras.
Concerning periclinal variegation, Ken showed a photograph of a section across the cylindrical leaf of Sedum rubrotinctum 'Aurora', where the circle of reddish-white tissue was obvious. From there it was a simple step to visualize the structure of any leaf like a flattened stem, and, given the eight different combinations of green and white in the three layers, how the two basic familiar patterns of periclinal variegation arise - pale middle and pale margin. The outermost layer, a thin skin with few chloroplasts at the best of times, does not contribute much to the appearance of a leaf, and hence can be largely ignored. This simplifies matters a lot. If the other two layers are the same colour, it will give a green or a white leaf. If the two layers are different: an innermost green layer will give a leaf with a green middle with a pale margin; an innermost white layer, vice versa. The trick is to note that the layer just under the skin is thickest near the edge of the leaf, where it turns over from topside to underside, hence it is only really here that its colour contributes to the overall appearance of the leaf. Ken's diagrams made all this much easier to understand! Hollies and ivies include a range of periclinal chimeras, some with pale middles, some with pale margins.
It should be noted that the asymmetrical striped variegation in plants like irises, may at first glance seem to provide examples of sectorial chimeras, but this has to be interpreted with care because one has to remember their leaves, at the base, are really folded in half along the middle - they may actually be periclinal chimeras.
Occasionally, white and green tissue layers may separate from each other and give rise to separate shoots. When this happens we say the plant has reverted. The green shoot will be too vigorous and should be pruned away so as to preserve the character for which the plant was originally grown. Green shoots also arise through root and leaf cuttings of chimeras, because of the way the new buds form.
[Those people who love to take clocks to bits just to see how they work, may like to note the following.] A plant's characteristics are normally transmitted to seedlings through genes in the nucleus of the cells. But the nuclei of cells in chimeral variegated plants contain normal genes; the variegation is determined by the chloroplasts elsewhere within each cell. However, this variegation can still be inherited by seedlings - if the aberration is in the layer of cells which gives rise to the ovules, which in turn become seeds.
Ken took questions from the audience and afterwards, including one common concern: What about variegations comprising various shades of green, yellow, grey
and other colours ? Ken had kept things simple (relatively speaking) up till now by pretending that the mutations affecting pigments were either on or off, and only affected the pigment chlorophyll. In fact mutations can affect any pigment, and to varying extents, giving rise to all the gradations seen.
Noon, and after deservedly hearty applause, Ann Maine gave a vote of thanks to Ken, then we all mumbled off to lunch, though full already by an hour and a half's ingestion of Ken's teachings.
Lunch, lubricated by copious amounts of tea, saw more rude pointing at plants and associated discussion or purchase. This was also a time to study the interesting posters and "The Enigma of Variegations" leaflets, courtesy of Hadlow College in Kent, which they produced originally for the 1996 Chelsea Flower Show. There were also display boards designed by students at Merrist Wood College for the same Chelsea show. Beryl Levett and others had contributed lovely large photos for display on partitions and walls. The hazy sunshine tempted us to seep into the charming grounds of Hall Place and take some fresh air. But before long it was one o'clock and we were summoned back to our seats, and, but little introduction needed, the well known Joe Sharman whisked us off into his afternoon's lecture.
JOE SHARMAN - VARIEGATED PLANTS IN A GARDEN SETTING
From his immersion in the nursery trade at Hilliers, Hopleys, and Langthorns Nurseries, and among the roses and shrubs at Albrighton, Joe emerged with the idea of starting his own nursery to propagate rare plants, including NCCPG 'pink sheet' plants. Hence Monksilver Nursery in Cambridgeshire was born. It now includes
variegated plants amongst its specialities. He has botanized and gardened in many corners of the world, always on the lookout for new material.
Joe defined variegated plants more widely than many folks do - any colour other than plain green, and including not just leaves, but flowers, seeds, roots, and stems. He showed us a bandy-variegated Equisetum to prove the last point, but I still don't think I want to risk one in my garden!
He explained how big collections of variegated plants have suffered mixed fortunes - for instance, that at Oxford Botanic Garden has been through ups and downs, and that at Chelsea Physic Garden was rejuvenated then done away with. But the National Collection of Variegated Plants at Heythrop Park, as visited by the HPS Berkshire Group, is in the good hands of Roger Boxall and his able gardeners. Roger took over the reins from Douglas Dawson, now retired, who deserves high regard for starting it. Why should interests vary over time ? And interests vary geographically, too…
The UK and Japan are two of just a few countries which seem to appreciate variegated plants, though interest may, hopefully, be expanding nowadays. In Boskoop and elsewhere in The Netherlands and in Germany nurseries with a special interest in variegated plants are coming into existence. On the other hand, Joe and Alan Leslie, his partner at Monksilver Nursery, spent hours scanning all the stock at a large Belgian wholesale nursery and found a trayful of oddities. When they tried to buy them the nurseryman refused to take any money for them. He was glad to be getting rid of what he saw as ill stock! Other countries have a similar attitude. But the picture is confused a little by a sort of snobbery - some plants being 'allowed' to be variegated - that is, variegated ivies, hostas and houseplants are OK. In the mid-west of the USA, variegated ground elder is grown simply because it is one of the few plants which will actually tolerate the extreme conditions of hot dry summers and cold winters.
So, interest varies, but Japan and the UK seem to have a real and more persistent passion for variegated plants - why ? Is it because plants, both wild and cultivated, in these countries produce more variegated sports ? In England there are some hundred or so varieties of Lawson cypress, some variegated, but none in the USA. Most of these originated by mutation here after the green species was introduced; very few variants have been found in the wild. Indeed, while living in the USA for a year, Joe found almost no variegated plants.
At this point discussion opened-up as to why Japan and the UK might be centres for plant variegation… I suggested it might have something to do with tea drinking, but while that raised a laugh, I did not see any heads nodding in consent. Steve Taffler wondered if it might be due to quality of observation, but Joe thought not - Joe had been keeping his eyes peeled wherever he went in the world, and said his impression was based on his personal observations as much as the collective observations of others. Further, Joe had seen non-variegated aberrations, such as doubled flowers, in many parts of Europe - it was just variegated plants that seemed to show the peculiar geographical distribution.
Another thought thrown-up for pondering: Why do some groups of plants produce more variegated sports than others ? For instance, amongst the many species of alder and birch [my examples] the closest we get to variegated forms is the odd "aureum"; whereas maples have many variegated variants. Also, within a groups of plants, such as maples, why are the same patterns of variegation not found amongst all species ? Sycamore, Acer pseudoplatanus, for example, has several mottled or streaky types but none with a pale border like the 'Drummondii' form of its relative the Norway maple, Acer platanoides.
Then Joe gave us a slide show quiz where the audience had to name the plant and say, going on our morning's education from Ken Burras, what sort of variegation it displayed. Good fun, and good photos. This also sparked some debate over which were the correct names for some of the varieties. I can't help feeling that Alan Leslie, who also wears a cap as senior registrar for cultivar names at the RHS, would have chipped-in his pennies-worth if he had been with us. To me, these seemed like dangerous waters I would do well to keep out of!
The spotlight moved to the tabletops in front of the audience, which were crammed with some of Joe's most interesting plants. He, with the help of Steve, held up plants for further identification and discussion, almost as if at an auction, putting the last remnants of his allotted time to good use.
Joe is clearly a keen observer with a questing mind, peering out from a vantage point of solid experience; it was a privilege to see a little way into the way he ticks. His talk was sprinkled with questions. At one point Joe speculated that golden-leaved plants, which become whiter when grown in a sunny spot, may have a type of chlorophyll which is actually destroyed by sunlight. Yes, there could be other mechanisms; that is not the only point. This is not an explicit question, but a thought worthy of sharing because of the questions it may provoke us into asking ourselves.
With never a dull minute, Joe had kept us entertained and had planted some intriguing questions in our minds. What fruit will grow, I wonder ? Ex-chairman Lorna Rutterford, in thanks to Joe, suggested his talk might be called 'Histories and Mysteries of Variegation', which I think sums it up very well.
STEVE TAFFLER - The Icing on the Cake
Steve, the reliably delightfully idiosyncratic co-founder in 1988 and secretary of the Variegated Plant Group of the HPS, lived up to his reputation for entertainment. He, tongue in cheek, as it were, demonstrated the making of a special cake icing from blood fish and bone meal and a good helping of chlorophyll for green colouring! Thankfully, the vision was transformed as his good lady wife, Gill, produced a big square cake, yummy down to the last of the real variegated icing.
That was a nice formal touch to mark the first Variegated Plant Study Day. But it wouldn't have happened unless, amongst many twists and turns of fate, Steve hadn't met Bill Archer forty or so years ago. Thence, a thyme called 'Doone Valley', named after Bill's house in Farnham, Surrey, came into Steve's hands and started his interest in variegated plants. He also became a hunter and collector of ivies, especially variegated ones, leading to his establishing the British Ivy Society in 1977 in collaboration with the American Ivy Society. Since then his fascination with variegation has been sustained by many sources, including an appreciation of the simple fact that leaves last longer than flowers, an educated ability to spot a departure from the norm, and a sense of fun. As if to prove the last point, Steve recounted a joke question from a gardener to a nurseryman: "Do you have any salivas ? No, but we have some spitoonias!"
He pointed out that of over a thousand variegated plants currently recognized, only some of those in about seven genera owed their variegation to a virus. Yet the feeling persists today in many quarters, as expressed by Reverend Berkeley in the 17th century "variegation is evidence of disease". Perhaps to the Reverend, Steve's next quip could be applied: "With fronds like these, who needs anemones ?"
We now also know that it was through the considerable efforts of Steve and Gill that the Plant Finder includes a little (v) after plant names to indicate that they are variegated, a fact by no means always obvious from the name (apart from the likes of 'Taff's Gold', I suppose).
After further amusements, Steve pointed out that our two visitors from Japan were authors of a new book on variegated plants from around the world. This is richly illustrated with 1350 colour photographs, and with four or five chapters on the history and study of variegated plants in Japan. It is due to go on sale in Japan at the end of December 1997, at which time it should be available for about £33. Steve will take orders, and details are in the Winter 1997 edition of ''The Sport'.
Steve expressed his happiness at how well the day had gone, made his own vote of thanks, and then Beryl thanked Steve.
Jane Sterndale-Bennett, chairman of the HPS, summarized the day and thanked Beryl, the committee and others from the groups who had made the day work so well. She was impressed with the range of variegated plants covered during the day, but left us with an implied challenge - to hunt out plants with variegation in both leaves and flowers…
Three O'clock, and there was just an hour left for last bargains from the plant stalls, last snippets of conversation, last nibbles at the cakes and sips of tea - a very pleasant winding down leading to the more introverted and subtle reflections en route home. What a marvellous inauguration of the Variegated Plant Study Day concept it was. I, amongst many, eagerly await the next recurrence. Thanks and praise for today's success must be given to Beryl Levett and the committee of the Berkshire Group, together with Steve and Gill Taffler, and a host of others too numerous, I apologise, to name - what good sports!
© Mike Hardman, 1997
with thanks to Ken Burras, Joe Sharman, and Keith Thompson for their comments