The Taxonomic Conundrum UnraveledBy Marie Harrison (can2grow)
October 18, 2011
Most flower arrangement designers never had to think beyond such names as mother-in-law's tongue or cast iron plant. The family name of plants does not have to be used in flower show schedules or for naming exhibits, so even the horticulturists have not been overly concerned with plant families. We do need to know the genus and species, and keeping up with generic name changes is challenging enough.
To begin with, hesitant designers felt comfortable just sticking their toes into the muddy taxonomic pool. They kept their Mono-botanic designs very simple by choosing a single plant. They knew that if the stems, seeds, and flowers of the same plant were used, they couldn't go wrong. Observers saw many designs with sunflower stems, seeds, and blossoms, or with palm spathes, stems, and blossoms or fruit.
Some designers, though, got braver and waded in the muddy water up to their ankles as they experimented with the Mono-botanic design. They learned, for example, that Rosaceae contains not only roses, but over 100 other genera, including apples, plums, and peaches, as well as nuts like almonds and ornamental berries such as those found on Pyracantha. They exhibited a multitude of beautiful designs from the family Rosaceae. Other designers investigated other families, and knowledge and creativity soared.
Then some designers became even more adventurous. They used plants such as Hosta, Aspidistra, Dracaena, and Sansevieria. But when they researched to find the families of these plants, they found themselves in deep water. In the case of Hosta, for instance, various references listed it as belonging to Agavaceae, Liliaceae, and Hostaceae. Aspidistra was found in Liliaceae, Ruscaceae, and Convallariaceae. Designers were in over their heads. "How can we," they wanted to know, "with our very limited knowledge of taxonomy, make a decision about all this?"
The Flower Show School Committee and Horticulture Instructors recognized the problem and took steps to simplify it. Their efforts resulted in a list of "Plant Families Frequently Used in Flower Shows" that can be accessed at http://www.gardenclub.org/. The list is helpful, and users can see at a glance that sometimes a single genus can be placed in different families. However, the list leaves a lot to be desired. There is no way that all the plant families and all the genera placed within them could be listed on a document that could fit inside a flower show exhibitor's Handbook for Flower Shows.
You may be thinking to yourself, "How did all this confusion come about? Aren't there rules governing the naming of plants? What about the International Code of Botanical Nomenclature? And anyway, what exactly is taxonomy, and why on earth is it important to me?
Let me give you an example. Let's say that two designers have used Aspidistra in mono-botanic designs. One lists it as a member of the Liliaceae family and combines it with Asparagus and some beautiful orange lilies. The other designer uses Aspidistra, but adds Dracaena and Sansevieria and identifies all plants as being members of the Ruscaceae, or lily of the valley family. Along comes the classification chairman who exclaims, "Oh, this can't be! Something is wrong! You two designers get over here and straighten out this mess! Aspidistra can't be in both the Liliaceae and the Ruscaceae families!" What do you think? Was one designer right and the other one wrong, or is there some possibility that both were right?
It helps to know a little about taxonomy and how it evolved. Taxonomy, as we know, is a system of classifying plants and other living organisms. Early taxonomists such as Aristotle and his contemporaries began classifying plants about 400 BC. Then Linnaeus, the Swedish scientist with whom we credit the system of binomial nomenclature still in use today, published Species Plantarum in 1753. His classification system was based mostly on the structure of the reproductive parts of a flower.
Linnaeus, as well as many modern taxonomists, base their classification on morphology, or the external features of plants that can be easily observed. With the development of modern research equipment, it has evolved into micro-morphological taxonomy. Equipment continues to be refined and improved, so now scientists can isolate such infinitesimal particles as the DNA of an organism, which contains the genetic instructions used in the development and functioning of all life forms. Still, though, we are speaking of morphological, or observable characteristics of plants.
About a century after Linnaeus, Charles Darwin challenged long-held beliefs about the origins of species. Basically he believed that taxonomic systems should be based on phylogeny, or the evolutionary history of organisms. Many modern systems rely on a combination of morphology and phylogeny. The newest systems classify plants based on their molecular structures, which more accurately reflects their phylogeny, or evolutionary descent.
So you begin to understand the situation. Taxonomists are using different criteria as the bases of their classifications. They are not wrong in their analyses, but we are left in a bit of quandary as we try to navigate among them. An internet search revealed at least 40 different systems of taxonomy, many of which had several revisions. How can we novices navigate among these different systems of taxonomy?
For most of us, it is enough to believe whichever trusted source we're consulting at any given time. We are sure to notice discrepancies, but as long as we know there is more than one correct answer, we're pretty much all right. If consistency is an issue, as is the case with writers and other communicators, it is important to choose one taxonomic system and stick with it.
To meet the need for consistency in this author's work, a system of classification was chosen that many organizations use, and one that is the result of collaboration and consensus among scientists from all over the world. It is called the APG-III System of Taxonomy. APG is an acronym for Angiosperm Phylogeny Group, and it is easily accessed on the GRIN (Germplasm Resources Information Network) website by anyone with a computer.
We know that NGC and Dave's Garden are not in the business of promoting one website over another-or one taxonomic system over another, and there are many that can be accessed. The GRIN website is being suggested in this case because it lists underneath each genus the different families to which plants are assigned by different systems, so one can see at a glance all the different (and correct) answers to the taxonomic conundrum. In addition, links to other databases are provided.
A particularly interesting document is James A. Reveal's "Concordance of Family Names." In this voluminous document, many family names are listed. Following each plant family, the family to which each is assigned by the revered taxonomic systems devised by APG-III, Cronquist, Dahlgren, Reveal, Stevens, and Takhtajan is shown. It is revealing to find that even these modern systems of taxonomy differ in their assignment of plants to families in some instances.
In our situations we are left to assume that all of the modern systems are right--or as right as humans can be in scientific endeavors of such magnitude. Each scientist or group uses the method of classification that is right for them. Remember, too, that independent researchers continue to publish their views about the taxonomy of plants. No classification is ever final. Each one presents a view at a particular time based on a particular state of research. New results appear frequently, and change will always be a factor with which we must contend.
The take-home lesson is this: There are many different systems of taxonomy. These systems use different criteria to classify plants. Consequently, a single plant may be placed in different families by various taxonomists. As casual readers, we can be aware of these differences in classification so that when one reference lists Sansevieria as a member of the Ruscaceae family and another assigns it to the Agavaceae family, we will not be confused. As soon as we are able to internalize this idea, the taxonomic quagmire begins to clear. We enter calm, sparkling waters, and gentle breezes carry us along as we sail confidently into the challenging sea of mono-botanic design and try to understand some of the complexities encountered in plant nomenclature.
In which family does Sansevieria belong? Various references list it in the following families: Asparagaceae, Convallariaceae, Dracaenaceae, Liliaceae, Ruscaceae, and Agavaceae. The APG III Taxonomic System places it in the Asparagaceae family. Similar findings are encountered when researching Dracaena, Hosta, Aspidistra, and other genera.
The taxonomic authority for the author's work is the GRIN (Germplasm Resources Information Network) online database, which is kept up-to-date with emerging taxonomic research and follows the most current system of taxonomy in its family classification, the APG III taxonomic system. The APG III system of taxonomy uses a phylogenetic (based on evolutionary development) and molecular approach to plant classification.
The thumbnail is a mono-botanic design by Barbara Baker of Fort Worth, Texas. In this design she used various members of the Brassicaceae family. The Rosaceae Mono-botanic design was done by Beth Wilson of Valparaiso, Florida.