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Why Plant Names Change

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Oh, my aching muscles...

...To Keep Gardeners on Their Toes

By Marty Wingate

"One of the liveliest and most predictable subjects of gardeners' conversation is the problem of changes in plant names, instituted for mysterious reasons by interfering botanists."

Brent Elliott, librarian for the Royal Horticultural Society, wrote those words in an article for the March 1994 issue of the journal The New Plantsman.  The article described the 150-year journey the Douglas fir took on its way to becoming Pseudotsuga menziesii.  It was an arduous trip, and full of changes--21 of them, in fact.

Gardeners shake their heads in disbelief at the fact that the botanical name for the Douglas fir was changed 21 times, and had a total of 19 different names.  Why would it take so long to reach a "correct" name?  Why would it be so difficult?  Why would a plant name need to be changed at all--and sometimes more than once?  Those questions are relevant not only to historical nomenclature events, but also to the changes that are occurring today.

Botanical names get changed for one or more of several reasons.  The reasons include the fact that the first name assigned was done so with insufficient knowledge of the plant's characteristics.  This shows the Linnaean classification method:  plant names were assigned according to physical structure, especially flowers.

During Captain Vancouver's 1791-1795 voyage, Archibald Menzies gathered the first sample of the Douglas fir for European botanists.  The tree was named Pinus taxifolia, in part because just about any conifer at that time was considered a Pinus, and also because the cone from the sample had been lost.  Here is a perfect example of lack of information leading to the wrong name.

The Douglas fir's story includes at least one other reason plant names change:  the rule of priority.  Sometimes a plant's botanical name changes back to an earlier name, which is deemed correct by taxonomists. 

Obviously, the name of a species of rose is not going to be changed to Daphne just because someone mistakenly called it that in a published article, no matter when the article appeared.  But if a legitimate name was published prior to a current name, then the switch takes place.  The genus name for the Douglas fir--Pseudotsuga--that was published in 1867 won that race.

You'd think that once all the rules have been followed and a name is applied, that would be the end of it.  But there are and probably always will be ongoing discussions within the taxonomic world over whether a species should retain this name or reject that name.  Looking at just a few titles of articles printed in Taxon, the journal of the International Association of Plant Taxonomy, shows us this. 

"Proposal to conserve the name Adenophyllum (Asteraceae)" by Kanchi M. Gandhi appeared in the May 2006 issue, while in the same issue "Proposal to reject the name Ipomoea glaucifolia (Convolvulaceae)" by George W. Staples was printed.  I'm not sure that we could say controversy rages over the subject of plant name changes--we're such a polite bunch--but it does appear to be a never-ending topic of debate.

You can probably think of some changes on your own.  Hosta used to be Funkia, some Gaultheria species used to be Pernettya, and Hebe used to be Veronica.  Hang on, come to find out Hebe has been put back into Veronica.  It's not a far-fetched decision: we can see the similarities between the spikes of tiny flowers in perennial veronicas and shrubby hebes, but still, it's slightly jarring to try and get used to.

It's possible that moving Hebe into Veronica has something to do with the way taxonomists--those who classify plants--work.  There are generally two camps of taxonomists:  lumpers and splitters.  Taxonomists who are lumpers see many plants in one group, while splitters like to dissect, splitting a genus into several genera.  The lumpers appeared to have won the battle of Hebe/Veronica.

Mahonia is another battleground.  Splitters contend that Mahonia (compound leaves!) and Berberis (leaves in three!  thorns!) belong to separate genera, but lumpers have long held the belief that all Mahonia species should be in Berberis.  You will find it both ways, depending on which catalog or book you read.

Occasionally the discussion of where a plant belongs, taxonomically speaking, takes a surprising turn.  Most gardeners are familiar with the Leyland cypress (x Cupressocyparis leylandii), an intergeneric hybrid of garden origin.

The parents of the Leyland cypress are the Alaskan cedar (Chamaecyparis nootkatensis) and the Monterey cypress (Cupressus macrocarpa).  Among taxonomists, there were always rumblings about this: many were not convinced that the parents were assigned the correct classification.

Then, in 1999, an entirely new plant was found in Vietnam.  It's a conifer, and was given the name Xanthocyparis vietnamensis.  Taxonomists realized the Alaskan cedar should be in the new genus, and moved it there.  Xanthocyparis nootkatensis it is!

Except that in 2004, another botanist pointed out an earlier published, legitimate name for the genus.  Here is the rule of priority again.  He proposes that the genus be Callitropsis nootkatensis, a name published in 1865.

And so it goes.

How long it takes for changes to filter down to the level of plant tags at nurseries is difficult to say.  When Actaea absorbed all the Cimicifuga species, it seemed a fairly short time before we saw the new names at the nursery.  Smilacina was taken into Maianthemum in 1986.  I had no idea that the starry false Solomon's seal in my garden is no longer Smilacina stellata, but Maianthemum stellatum.

Look for more changes, especially with the ability to compare DNA samples from different plants.  The American asters are under fire, and strawberries (Fragaria) may move to Potentilla.  Be assured that any changes in plant names have been discussed thoroughly by taxonomists.  Although that doesn't mean they can't change their minds.  Again.

Do you want to know more?

All the rules for assigning plant names are in The International Code of Botanical Nomenclature (ICBN).  You can find a copy at the Elisabeth C. Miller Library, but I must tell you it's dry reading--rules, rules and more rules.  Information online at: www.bgbm.fu-berlin.de/iapt/nomenclature/code/SaintLouis/0000St.Luistitle.htm

I keep up with the gardener's version of botanical news by reading the Royal Horticultural Society's journal The Garden.  To check on correct names, I pick up The Plant Locator: Western Region by Susan Hill and Susan Narizny (Timber Press, 2004, $19.95) or go online to the RHS Plant Finder site: www.rhs.org.uk and the reverse synonym finder page at: www.rhs.org.uk/rhsplantfinder/reversesynonyms.asp



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