origins of rhododendrons in North America

Discussion in 'Plants: Science and Cultivation' started by Eric La Fountaine, Mar 9, 2004.

  1. Eric La Fountaine

    Eric La Fountaine Contributor UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    Hello - I am trying to find out about the origins of rhododendrons in North America and am getting much conflicting information. The British forestry commission claims that this international invasive is strictly Asian in origin, whereas, two North American states claim the flower as their own, Author Sonja Nelson claims the rhododendron was first discovered in 1792 by Archibald Menzies, botanist (1754-1842), on the shore of Puget Sound; what is the real truth here? Is this an introduced plant brought by early settlers that has run wild across the continent, or is it a North Western and Appalacian long time resident, and if so, what are the current theories on how it got here from Asia and how long ago? Please help me to answer this authoritatively, I recently claimed this plant was a recent invasive, and wish to either confirm or refute with detail this statement.
     
  2. Chris Klapwijk

    Chris Klapwijk Active Member 10 Years

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    We have 22 or 23 native species of rhododendron (see this and this page; some experts no longer consider R. camtschaticum to be a rhododendron)
    Native to Western North America are:
    R. albiflorum
    R. camtschaticum
    R. groenlandicum
    R. lapponicum
    R. macrophyllum
    R. neoglandulosum
    R. occidentale
    R. tomentosum ssp. subarcticum


    Native to Eastern North America are:
    R. vaseyi
    R. canadense
    R. canescens
    R. austrinum
    R. flammeum
    R. periclymenoides
    R. alabamense
    R. atlanticum
    R. calendulaceum
    R. prinophyllum
    R. viscosum
    R. arborescens
    R. cumberlandense
    R. prunifolium
    R. eastmanii


    Which one would you be referring to, R. macrophyllum?
     
  3. dunning

    dunning Member

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    Missed a few

    You missed all the evergreen native rhododendrons of eastern North America:

    R. minus
    R. catawbiense
    R. maximum

    Any others?
     
  4. Chris Klapwijk

    Chris Klapwijk Active Member 10 Years

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    So I did and I'm at a loss to explain how I managed to miss them.

    See here and here for some detailed rhododendron history.
     
  5. dunning

    dunning Member

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    Invasive Rhododendrons

    The British forestry service may have cause to complain since they have an alien ponticum taking over large streches of the moors. I attended a lecture in 1997 where the speaker said the ponticum had genetic affinities with both species in Portugal and species in North America. That sounds rather unlikely since North America and Portugal have not been in touch for some time. Even the helpfulness of British gardeners in reuniting these lines does not seem likely to create the genetically superior alien that is now rampaging across the moors.

    There does not seem to be any similar problem in North America. I have seen R. macrophyllum taking over vacant lots in Florence, Oregon, and in clearcuts in Washington state, but R. macrophyllum is a native in those places.
     
  6. Chris Klapwijk

    Chris Klapwijk Active Member 10 Years

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    R. macrophyllum, R. ponticum, R. catawbiense, and R. maximum all belong to subgenus Hymenanthes, section Ponticum, subsection Pontica and as such are very closely allied.
     
  7. alanShort

    alanShort Member

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    A reply from Offwell Woodland & Wildlife Trust

    I received this informative email from Offwell Woodland & Wildlife Trust, I have deleted the name of the ecologist, as she might not appreciate my posting her name on the internet without permission.
    Email me directly if you would wish to contact her.

    Quote

    I am afraid that I am unable to give you the definitive answer to your question that you are seeking. Indeed, I would not be surprised if there was actually no definitive answer. The delay in replying has been due to my trying to collate my existing knowledge so that I could pass it on to you.

    I will try to give you the short answer first and then to expand it below so that you have a bit of extra information if you want it.

    The answer to your query depends initially on which species of rhododendron you are concerned with. There are literally hundreds of different species of rhododendron. Some of them may be native to America, while others have certainly been introduced and can be reliably classified as aliens.

    In searching the web, I have come across approximately 25 rhododendron species which are quoted as being native to America. I am unable to comment on the truth or otherwise of this. Most rhododendron species are of eastern Asian origin, with comparatively few species in Europe and North America. These latter may either be native, having been derived from the natural spread of rhododendron across historical land bridges, or else have arrived through artificial introduction.

    In order to judge whether a plant species is native or not, it is necessary to look for clues in the following:

    1. Historical records of introductions and discoveries of species.
    2. The fossil and/or pollen record of particular areas.
    3. The number of invertebrates which feed on the plants.
    4. The genetics of individual plants and species in different localities.

    The Trust's experience and knowledge of rhododendron is mostly concerned with that occurring in Britain and specifically with Rhododendron ponticum, which causes most of the invasive problems in the UK. I am therefore not aware of whether such research into the 'nativeness' of the American rhododendron species exists or not. I did not come across it in my internet search, but it may simply be that it has not been published on the internet (or at least not in a form that is easy to find).

    That is the short version!

    Here are a few other points which you might wish to consider or which might help to widen your search.

    1. What is the definition of native?

    Plant introductions have been going on for centuries and probably extend far back into our neolithic origins. Unless reliable records have been kept, it may be next to impossible to know whether a plant is a true native (ie naturally occurring in the area) or whether it was introduced to the area centuries ago and has since become thoroughly naturalised. (A naturalised species being one which has been imported, but which has escaped cultivation and gone on to form self-sustaining populations in the wild.) In Europe, distinctions are sometimes drawn between species which are classified as 'archaeophytes' (imported prior to around 1492, which excludes species from America) and 'neophytes' (imported after this).

    2. The pollen record

    Failing the existence of reliable historical records, other ways to trace the history of plants in a particular area include looking at the fossil pollen record preserved in the soil. This is usually only possible in very boggy soils where preservation of organic remains is good because of the exclusion of air. How useful a clue this is for a particular plant species depends on a number of factors. These include the resistance of its pollen to degradation, how distinctive the pollen is and whether the plant has grown near enough to boggy areas for the pollen to be carried/blown into the bog soils and preserved. Absence of pollen from a particular plant species in the pollen record does not necessarily equate to absence of the species historically.

    3. Associated invertebrates

    Another clue to the length of time a plant has been present in an area is the number and variety of invertebrates (pests in gardening terms) which eat it. It is obviously possible for pests to be imported along with the plant and to be able to survive their relocation together with the plant. However, the greater the number of pest species a plant has, the more likely it is that it has been in an area for a long time, or that it is native.

    This makes the assumption that a sufficient time period must elapse in order for local invertebrates to evolve to eat an unfamiliar plant. However, this may not be true in all cases. Where an imported plant has a very similar chemical composition to other locally occurring plants, adjustment of the local bugs to the new food source may be easy. Nevertheless, it is likely that this is a relevant consideration for rhododendron, because many rhododendron species seem to be particularly toxic to herbivores. It is therefore likely to require a considerable amount of evolutionary adjustment before unfamiliar invertebrates are able to eat it without it being fatal.

    The lack of controlling herbivorous species is one of the factors often contributing to the invasive properties of many such alien plant species.

    4. The origins of rhododendron.

    There are around 1200 species of rhododendron. The great majority of these are Eastern species found in China, Tibet, Burma, Assam, New Guinea, the Himalayas and Japan. Comparatively small numbers of species occur in Europe and North America. To me, this would tend to suggest that rhododendron originated in the East and colonised other areas by spreading outwards both naturally and by introduction. (However, this is my supposition and is not backed up by research. I have been unable to find specific references.) If this is the case, then presumably rhododendron might have colonised North America across the land bridge which existed at one time. I include the following quote for you from:

    Molecular systematics of Rhododendron ponticum (Ericaceae) and its close allies
    by Dr. R. I. Milne; BBSRC CASE studentship in collaboration with the Royal Botanic Gardens - Edinburgh; Supervisor Dr. R. J. Abbott

    "A preliminary cpDNA phylogeny was provided for Rhododendron subsection Pontica (R. ponticum and its 11 closest relatives). The group has a "Tertiary Relict" distribution (Japan, N. America and Turkey) and there was considerable discordance between clade membership and geographical location, indicating that speciation predated migration. Migration to America via the north Atlantic land bridge was hypothesised."

    This would suggest that certain rhododendron species may indeed be native to North America. Dr Milne may be able to give you more information on this.

    Rhododendron in Britain

    There is some debate over whether Rhododendron ponticum in Britain was introduced from Asia or the Mediterranean (this is what you will have read about on our website).

    Some research has recently been carried out (again by Dr Milne, quoted above) which compared the genetic material of R.ponticum in Britain with that of R.ponticum in Turkey, Portugal and Spain. The genetic material was found to be very similar and it has been suggested that this proves the Mediterranean origin of British R.ponticum. However, in order to get a definitive answer, I think that it would be necessary to compare the genetic material of British R. ponticum with that obtained from the same species in Eastern regions. I am not aware that this has actually been done, although I may be wrong. I did correspond with Dr Milne regarding this matter and I include the text of his email reply below.

    "Rhododendron ponticum is native to SW Spain, two small regions of
    Portugal, the are around the S coast of the Black Sea (extending from
    Bulgraia to the Caucasus but most abundant in NE Turkey) and Lebanon. I
    sampled material from Spain, Portugal and three parts of Turkey, and the
    British plants matched cpDNA-types unique to Spain, or in 10% of plants,
    Portugal.
    R ponticum is part of subgenus Hymenanthes of Rhododendron, which
    contains 3 spp in America, 4 in SW Asia (including R ponticum which
    extends into Europe), 3 in Japan and the remaining 215-odd in S china andf
    the Himalayas, leading ot the popular misconception that all Rhododendrons
    come from this region.
    The British R. ponticum certainly contains genetic material from
    the American R. catawbiense, and to a lesser extent R. maximum also from
    the USA. I believe, though I'm still seeking hard evidence, that
    hybridisation with these species has increased the cold-tolerance of R.
    ponticum in the UK and enhanced its invasiveness here. In effect, it is a
    GM plant!
    However, there may also have been hybridization with some of the
    E Asian species, many of which are grown in gardens though none are as
    hardy as R. ponticum. However these can have had little or no effect on
    its ecology."

    It is possible that R.ponticum originated in the east and spread westwards to the Mediterranean either through introduction or naturally. It could also have been separately introduced into Britain from the East. In this scenario, the Mediterranean plants and the British plants would both have come from the same original Eastern genetic stock. It would therefore be logical for them to be very similar genetically, without the necessity for the British rhododendron to be directly derived from the Mediterranean. In the absence of this comparison, I think the question is still open to debate.

    I would suggest that to further your query you need to:

    Find out which species of rhododendron you are concerned with.
    Check to see if there are historical or pollen records to confirm that it is native.
    See if there has been any research on its genetic relationships.
     
  8. dunning

    dunning Member

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    American Native Rhododendrons

    There can be little doubt of the authentic american native birthright of a large number of evergreen and deciduous rhododendrons. If there were a third spot in the world after the himalayas and the malaysian archipelago where one can observe adaptive radiation in rhododendrons, it would be the american southeast. This is especially true of the deciduous azaleas of that region.

    Countless afficionados in the Carolinas would be surprised to hear a british ecologist express uncertainty about that.

    I enjoyed reading about the genetic analysis of the british ponticum. It perfectly captured my state of perplexity on the subject.
     
  9. Daniel Mosquin

    Daniel Mosquin Esteemed Contributor UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    If you live in the Vancouver area and are interested in the subject of the distribution of closely-related Asian and North American plants, please consider attending Dr. Michael Donoghue's Biogeography of the Northern Hemisphere seminar on April 8.
     
  10. Rhebecca

    Rhebecca New Member

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    Glen Magna Farms in Danvers, Massachusetts claims they have the first rhododendron plant to be brought to North America, so you could reach out to them.
     
  11. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Since there are roughly 25 or so native rhodies that predate human introduction, wouldn't it be a little silly to claim to have first brought them to someplace where there were lots already?
     
  12. Rhebecca

    Rhebecca New Member

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    Perhaps; I can only repeat what the groundskeeper told me, but you could contact them and see what they say. You never know what you’ll learn.
     
  13. Margot

    Margot Well-Known Member

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    Here's the way I read it, knowing that at one time, the only rhododendrons in NA were indigenous but now, hundreds originate elsewhere.

    It is quite possible that the first exotic rhodo brought to NA is growning at Magna Farms.
     
  14. Ron B

    Ron B Paragon of Plants 10 Years

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    Dispersal occurred from north‐east Asia to North America throughout the late Eocene and Oligocene

    (Link works for me, despite the title it was given here)

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