JARS v63n2 - The Word: Taxonomy
The Word: Taxonomy
Have you planted the rhododendrons you picked up at the last conference? If you're like me you haven't. Now would be a good time to get them in the ground. As you're putting on the new labels have you wondered how in the world your species plants got such weird names? Some of the answers lie in this issue of "The Word: Taxonomy."
Taxonomy comes from the Greek "taxis" = arrangement, and "nomos" = law. Taxonomy is generally considered to include the disciplines of classification, identification and nomenclature. What it means to us is a system of artificial rules that attempts to make sense out of what appear to be relationships among organisms. We humans need to make sense of nature on our terms even if our ideas don't fit the real world. This practice in the western world dates to the Greek and Roman philosophers, notably Theophrastus, a student of Aristotle, in about 320 B.C. He classified about five hundred plants by their growth patterns and life spans. As time went on other people "improved" the system of classification until by the middle of the eighteenth century it was a total mess. By that time long, descriptive Latinized names were the norm (Woodland, 1991). Rhododendron maximum , the well-known rhododendron, commonly called Rosebay, growing in Eastern North America from Nova Scotia to Georgia, was called Chamaerhododendros laurifolio, sempervirens, floribus bullatis corymbosis (Leach, 1961). Very roughly translated, this means low-growing rhododendron with bay-like leaves and puckered flowers in an open truss.
In the eighteenth century, building on the work of his predecessors, Carl Linnaeus, a Swede trained as a physician, began to classify everything, living organisms and rocks included, by a more simplified Latinized system of naming. Linnaeus is considered to be the father of modern taxonomy where we use a unique two-part Latin or Latinized name for every organism. We call the name a binomial. Today the two parts of the binomial are referred to as the genus (Greek: genos = race) name and the specific (Latin: = kind) epithet. Linnaeus named our beloved genus Rhododendron . He took the Greek word for oleander, Rhododendron (Greek for rose tree), and applied it to the plants we now know as rhododendrons. He wasn't the first to do so, but he formalized the name. One of the rhododendrons of which Linnaeus had specimens was what we now know as Rhododendron maximum L. Note that the modern system calls for the genus name to be capitalized and the specific epithet to begin with a small case letter and to have a Latinized ending. The binomial name is followed by the name or an abbreviation of the name of the person who assigned the scientific name, thus "L." is used for Linnaeus.
A genus name is unique within a taxonomic Kingdom (more about Kingdoms later) such as the Plantae, and a specific epithet is unique within a genus, but the same genus name can be used in other Kingdoms. For example, the common cabbage butterfly, Pieris rapae (Kingdom Animalia), has the same genus name Pieris (Greek collective name for the muses) as the Japanese Andromeda, Pieris japonica (Kingdom Plantae).
All of this is governed by a set of rules called the "International Code of Botanical Nomenclature" (ICBN)). The code was adopted internationally in the late nineteenth and early twentieth centuries but many of its provisions, for example priority naming rules, derive from Linnaeus' suggestions in 1753. The ICBN is revised periodically, with changes made retroactive to 1 May 1753. Major revisions are named after the cities where they were adopted; thus the most recent version is called the Vienna Code, adopted in Vienna in July, 2005 (McNeill et al., 2006). Originally in biology there were only two codes, one for botany and one for zoology. As more discoveries have come along and it has become clear that there are more than two major groups of organisms, codes have been developed for such groups as bacteria and viruses, among others, as well as a separate code for cultivated plants.
The name Rhododendron maximum has stood the test of time since Linnaeus as the binomial for the rhododendron commonly called Rosebay. That is probably more the exception than the rule. Plant names often go through a series of changes over time (Voss, 2009). The changes, though, are orderly and are governed by priority rules in the ICBN. The genus Rhododendron has by far the largest number of species in the family Ericaceae (the heath family). The genus is so widespread and diverse compared to most other genera that it has been subdivided in varying and ever-changing ways (Cox and Cox, 1997), but this is a topic for another time.
At the taxonomic levels above genus, ideas are, if anything, more in flux. Before improvements in the light microscope, the invention of the electron microscope and advances in genetics and biochemistry, biologists (Greek: bios = life and logos = discourse) recognized two great groups of organisms, plants and animals. This formed the basis for the taxonomic hierarchy based on two Kingdoms, Plantae and Animalia. It also fostered the division of biology into botany and zoology. The separation persists to this day and causes problems in many areas, including taxonomy. The hierarchy constructed early on and in use until quite recently was, starting at the top: Kingdom, Phylum (more usually Division in botany), Class, Order, Family, Genus and Species. Each category could be subdivided into sub- and super- categories with various names. For Rhododendron maximum , until less than a generation ago, this was: Kingdom Plantae, Division Spermatophyta, Class Angiospermae, Sub-class Dicotyledoneae, Order Ericales, Family Ericacae, Genus Rhododendron and Species maximum (Gilkey and Dennis, 1975).
As more information has surfaced about living and fossil organisms, categories at all levels have changed. The top category, Kingdom (now often called Regnum) was obvious before advances in biochemistry and microscopy, but it isn't anymore. It is now clear that there are several more Kingdoms than two or possibly none at all. Major differences are now recognized above the Kingdom level, at what we call Domains. At this level we now differentiate organisms based on their cellular structures (presence or absence of a nucleus) and on their chemistry. There may be two or three Domains, depending upon how the issues are viewed. At the level next below Kingdom (Regnum), there is a semantic issue that puts botanists and zoologists at odds with their separate international codes. Zoologists use the term phylum, but botanists prefer division, though phylum is acceptable. In zoology, the term division has been used below the genus level. At the lowest level, species, we have never been quite sure what we're talking about. Definitions vary, but a species is often defined as a group of similar organisms that interbreed freely but do not usually interbreed with other groups of similar organisms. We biologists tend to assume that we know what this means, but clearly the definition is pretty muddy. One current example of this is R. maddenii . Once R. maddenii , R. polyandrum , R. callophyllum and R. crassum were assigned to separate species. Now, based on new specimens, observations from the wild and reexamination of old specimens, they and some other former species are grouped together under Rhododendron maddenii (see Cox and Cox (1997), p. 287 for a good explanation).
So, why not forget about all this and use common names when the Latinized ones are so hard to pronounce? Although scientific naming is in constant flux, it offers a universal designation system that doesn't change from one place to another, as do common names. If you go to an ARS conference and use the name rosebay, chances are most people won't know what plant you are talking about. If you use Rhododendron maximum , though, they probably will. Besides, when we're out in our gardens enjoying our species rhodies in bloom, it's interesting to know that someone put a lot of effort into naming it properly.
If we're really curious, we can look up the details. For evening reading, I can recommend highly Anna Pavord's (2005) book "The Naming of Names." Here is a book aimed at interested lay people that deals primarily with taxonomy before Linnaeus, beginning with Theophrastus in about 320 B.C. It has 159 illustrations, nearly all full page color plates. It contains a wealth of information and is written in a clear, captivating style. At its original price of $45, it is a real bargain, but it can be obtained on www.abebooks.com for much less.
Cox, P.A. and K.N.E. Cox. 1997. The Encyclopedia of Rhododendron Species . Perth: Glendoic Publishing. 396 pp.
Gilkey, H. and L.R. Dennis. 1975. Handbook of Northwestern Plants . Corvallis: Oregon State University Bookstores. 505 pp.
Leach, D.G. 1961. Rhododendrons of the World . New York: Charles Scribner's Sons. 544 pp.
McvNeill, J., F. R. Barrie, H. M. Burdet, V. DeMoulin, D. L. Hawksworth, K. Marhold, D. H. Nicholson, J. Prado, P. C. Silva, J. E. Skog, J. H. Weirsema and N. J. Turland, Eds. 2006. International Code of Botanical Nomenclature . Vienna: International Association for Plant Taxonomy.
Pavord, Anna. 2005. The Naming of Names , The Search for Order in the World of Plants. New York: Bloomsbury Publishing. 471 pp.
Voss, D. 2009. How plants get too many names. J. Amer. Rhododendron Soc . 63(1): 10-14.
Woodland, D. 1991. Contemporary Plant Systematics . Englewood Cliffs, N.J.: Prentice-Hall. 582 pp.
Bruce Palmer is a member of the Eureka ARS Chapter. He was a teacher of biology at Maui Community College in the University of Hawaii system for 25 years.