Taxonomy – A Taxing Topic

by Norman Todd  October 2004


As a grower and a small time merchant of rhododendrons, who has had no formal training in subjects to do with plants or indeed anything to do with living things, I am often at a loss to understand why there is so much fuss about what to call a wild plant.  There is no mercy spared, as was by another more famous merchant *, by those concerned with assigning plants names on the users of improper names.  To keep themselves in business and keep the nomenclatural brew boiling they keep changing the plants’ names.


People who give living things names are called taxonomists.  Here are a couple of examples of the writings of a rhododendron taxonomist:  “Inflorescence terminal, 1- or sometimes 2-3 flowered…” and “…with closely or widely scattered dark brown scales.”  The uninitiated might think that whether a plant had one or three flowers would be important.  And the novice might think that describing the spacing of the scales on a leaf, as being ‘close’ or ‘wide’ would cover every possibility that could exist and be of absolutely no help in differentiating one scaly leafed plant from another.  Being a good taxonomist requires the special skill of being accurately vague.


Professor David Rankin of the University of Edinburgh says in an ideal world we would have taxonomy machines.  “Into one end we would feed bits of plants, and at the other end we would be presented with a few Latin words, as well as small amounts of compost.”  However, this Garden of Eden that we live in is not completely ideal. No matter how elegantly discriminating the classification system devised by taxonomists becomes, nature is in flux and there is a continuum in the differences between living things. Darwin famously wrote about the origin of species and brought to our notice the fact that the survival of the fittest relied on changes in living things — an ongoing process — making individual taxons moving targets.


At the 2005 convention, which we will host, we will hear about some of the work being done to make the differences between what we call species (taxons) more precise. It is doubtful, however, if the distinctions will make it any more clear to a gardener why he has to make a new plant tag.


 In the early day of the science of taxonomy, it was thought that the shapes, sexual function and numbers of different parts of a plant would be sufficient to distinguish one kind of plant from another.  For example, if a flower had five petals on one plant, that would make it a different kind from another plant that had seven petals on its flowers.  I would intuitively think the number of lobes or petals on a flower would be an important characteristic.  My plant of rhododendron ririei is an example showing this is not the case. (I know it is rhododendron ririei because that is the name that was on the label when I acquired that plant.)  Some of the flowers have five lobes on each corolla, some have seven.  Consequently, I can accept that the number of lobes is not a good measure.


The classification experts have grouped some species together into Sections and Subsections.  Plants are grouped like this because they have similar features.  R. ririei is placed in Subsection Argyrophylla.  R. ririei has prominent nectaries.  Ririei is the only one in this Subsection that has nectaries.  Intuitively, I would think that would be a significant distinction but evidently it is not.  I am now waiting for some expert to say my plant is not ririei at all; or to be told that its closest relatives are not in Subsection Argyrophylla and it should be slotted into some other part of the genus’s spectrum; or even worse, the experts could decide that it is not a species at all but a hybrid.


I think it’s important to recognize that the main reason for trying to place plants into tidy slots is so we can communicate.  For this same reason, we use a universal Latin-like language.  It’s all about being able to talk to each other.  It’s also important to remember that speciation is one of the fundamental processes in evolution.  A very general definition of what makes a species a species is that the members included are able to breed among themselves but generally not easily with others.  There are well known examples of hybrids, i.e. inter-specific crosses, like the mule — the offspring of a horse and a donkey.  But we all know how easily large numbers of species in the genus rhododendron behave promiscuously and mate with every Tom, Dick, Sally and Sue to produce hybrids.  Unlike the mule, these are most often not sterile. As a result, the majority of the rhododendron plants we grow in our gardens are, in fact, hybrids.


Over 30,000 hybrids are considered by someone, somewhere to be worthy of a birth certificate and be registered with the botanical authorities at Wisley, England. Unlike species, once a hybrid’s name has been entered into the record it cannot be changed.  R. ‘Hoppy’ — one of the Seven Dwarfs —should be R. ‘Happy’ but was incorrectly spelt on registration and no deed poll can change that.


Jane Brown, in a new (2004) book on rhododendrons, ‘Tales of the Rose Tree’ writes that, “Rhododendron taxonomy is a path to lonely sainthood, pursued in chilly garrets and overheated laboratories.”  And, “Taxonomy is a rolling sea of knowledge, entered at great peril; the lists and classifications are the bulk tankers of the rhododendron world, necessary but ugly and best left to go about their business unheeded.”  I’m not quite comfortable with this tanker analogy but it does highlight the facts that only Master Mariners can command them, that classifications keep moving and that they are very unwieldy.


Despite all the difficulties of getting the right name on your plants, the effort involved in trying to determine that correct name is really a worthwhile exercise — better not left unheeded — and can add significantly to the enjoyment of growing a plant.  But don’t take it too seriously.  The late Mrs. Berry of Washington State had a large collection of rhododendrons, many of which were grown from seed.  She would be visited every year by a succession of the world’s plant experts and would ask, label in hand, each expert to identify her plants.  At the end of the year she would have six or eight names on a plant.  Come the New Year she would clear off all the tags and begin again.


*[Ed. Note “The quality of mercy is not

It droppeth as the gentle rain from heaven

Upon the place beneath: it is twice blest;
It blesseth him that gives and him that takes…”

(Act 4, Scene 1, Shakespeare’s Merchant of Venice)

After finding Norman’s 'Merchant' on Google, I had the pleasure of reading half the play again, before locating Portia's fine lines.]