Although at times they are a mouthful to say, we can all concede on some level that scientific plant names have their uses.  They provide a systematic way of referring to plants by using unique names that dispel the confusion that common names create.  L.H. Bailey, in his 1933 book How Plants Get Their Names, explains the necessity of scientific names with an enjoyable description of the Jerusalem cherry, which, he points out, is neither a cherry nor from Jerusalem.

As with any other system, there are rules, and the rules come from some governing body, often self-appointed.  Grammar rules come from our eighth grade teacher, or so it seemed, style rules come from Strunk and White, and the rules of order for a meeting come from Roger.  But whence the rules for plant names?

The plant classification system itself comes from the mid-18th-century Species Plantarum by Carl Linneaus.  In that work, Linneaus first published the system for organizing plants and assigning them a binomial, a two-word name for a species.  The International Association for Plant Taxonomy (IAPT) maintains the set of rules for naming; it is called the International Code of Botanical Nomenclature.

Who Makes the Rules?

The ICBN is the set of rules that provides taxonomists the guidelines for assigning names to plants, and checking on existing names if a controversy arises about the correctness of a plant name.  When the IAPT meets, an updated set of rules is published and the update is referred to by the place where the meeting was held.  So, the most recent code is called the St. Louis code, named for the International Botanical Congress held in that city in 1999; before that, the Tokyo code (1993) was enforced.

Unless you are a scientist, reading the code is rather dry work, even for someone who loves to learn and say scientific plant names.  The code deals with such topics as what happens when the specific epithet is in the form of an adjective or a noun, what is a validly published name, and how to form infraspecific epithets.  You may want to read through the code yourself, and so here it is on the Web:  www.biologydaily.com/biology/International_Code_of_Botanical_Nomenclature

But it is more likely that you are interested in plant name topics that hit closer to home.  And one particular topic of interest is why plant names change.  That, too, is described in the code, but let's look at some particular examples that can make sense of the scientific language.

Changing Names

In The New Plantsman, March 1994, Brent Elliott, who is the librarian for the Royal Horticultural Society, expressed the frustration of many gardeners when he wrote:  "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."

This was the introduction into the subject of the many scientific names that have been applied to the Douglas fir, Pseudotsuga menziesii, over the last two hundred or so years.  Elliott's story of the Douglas fir name changes has to do with the rule of priority.  That rule states that the correct name of a plant is the first published correct name.  It must be correct; it must be published; it must be first.

It began when Archibald Menzies collected a specimen of the tree while serving as naturalist on Captain George Vancouver's 1791-1795 voyage.  Unfortunately, the cones had been lost, and that made any identification or classification difficult right from the beginning, because Linneaus's entire system was built around categorizing and naming plants by their sexual parts.

So, the first name applied to the Douglas fir was Pinus taxifolia.  It was a pine, because at that time almost any conifer was considered a pine; the second word easily described the look of the needles, which resemble a yew (Taxus).  This was in 1803.

In 1825, the third name given to the Douglas fir was Abies menziesii, suggesting that the tree be named for the man who first collected the specimen.  From there it's a merry romp through more firs (Abies), more pines, a spruce or two (Picea) and a couple of hemlocks (Tsuga).  All the while, the specific epithet (the second word in the name), also bounced around.  It was not until 1867 that a new genus, Pseudotsuga, was proposed, and the taxifolia was added.  But, in 1950, it was pointed out that the specific epithet taxifolia had been misapplied when the tree was thought to be a pine or a fir.  And so the specific epithet was changed to menziesii, which was the first published correct name.

Got that?  So, in 1950, the Douglas fir's scientific name settled down. 

Your clue to the fact that a plant has had other names can be found when, after a plant name, you see parentheses and the abbreviation "syn."  For example, the California fuchsia, Zauschneria, was formerly listed as an Epilobium, the genus of fireweed.  The listing would appear:  Zauschneria californica (syn. Epilobium canum).

Plant names can change after years of debate-or sometimes, the debate continues and gardeners' heads go back and forth as if we were watching a tennis match.  The two camps held by taxonomists on the Mahonia/Berberis debate (some felt all the species should be Berberis) appears to have decided that their really are two genera there.  On the other hand, there is still a large contingent of taxonomists who include Pernettya in Gaultheria, and so you may see them lumped together in some references. 

Recent Discoveries

At other times, a precipitous event causes something akin to fruit basket mixup.  Case in point:  the Alaska cedar, Monterey cypress and their offspring, the leyland cypress.

The leyland cypress has been known by the botanical name x Cupressocyparis leylandii.  It was a cross between two West coast species, the Alaska cedar (then known as Chamaecyparis nootkatensis) and the Monterey cypress (Cupressus macrocarpa) which occurred in, of all places, Leighton Park, Wales in 1888.  An intergeneric hybrid is noted by the "x" at the beginning of the name; the genus  name for leyland cypress was formed by combining the parents' names.

Even before 2001, taxonomists were uncomfortable with the placement of the Alaska cedar in the genus Chamaecyparis (the genus is sometimes called "false cypress").  Perhaps it was really a Cupressus, in which case the leyland would be an interspecific, not intergeneric, hybrid.  But when a new conifer was discovered in Viet Nam in 2001, it seemed to settle the controversy for all the scientists.

The new genus was given the name Xanthocyparis, and the species found, Xanthocyparis vietnamensis.  Xanthocyparis is described as the link between true cypress (Cupressus) and false cypress.  With what seemed like a huge sigh of relief, Chamaecyparis nootkatensis was moved into the new genus, and renamed Xanthocyparis nootkatensis.

This meant that the leyland cypress was still an intergeneric hybrid, but one parent's name had been changed, and so must the leyland's.  The correct name is now x Cuprocyparis leylandii.

Don't expect the plant name dance to stop.  Now, with the ability (but perhaps not all the funding in the world) to describe the DNA of a plant, more changes are to come.  Just within the last couple of years, gardeners have seen the genus bugbane (Cimicifuga) moved into the baneberry genus (Actaea).  That means that the lovely, dark-foliaged 'Hillside Black Beauty' is now Actaea simplex 'Hillside Black Beauty'.

Our Garden Plants

Next after scientific names, gardeners focus on the cultivar names of plants—that part of a plant name within single quotes.  The rules for cultivar names are the responsibility of an organization related to the ICBN; it is the International Code of Nomenclature for Cultivated Plants. 

The ICNCP keeps a sharp eye on cultivar names, and hopes to clarify the whole subject for gardeners.  For example, one rule passed in the late 1950s stated that cultivar names should not sound like Latin, so that gardeners won't be confused about which part is the scientific name and which part is the horticultural community's name.  Granted, many plants were given cultivar names before that rule was passed, and so we continue to find Viburnum opulus 'Roseum', whereas today that 'Roseum' would be changed to something less latiny.

The ICNCP includes more than 70 International Cultivar Registration Authorities (ICRA) focussing on some of the most popular groups of garden plants; the overseeing organization is the International Society for Horticultural Science.  ICRAs are worldwide and, in most cases, are a particular plant society.  For example, the American Fuchsia Society, the Heather Society and the International Oak Society, both based in the UK, and the Bromeliad Society International in Australia are all ICRAs.

It may seem like a lot of to-do over one little four-inch perennial you see at the nursery.  But in fact, if we did not have all those botanists constantly sifting through research and previously published plant names, we would soon sink into the morass of the quirky world of common names.