Orchid Taxonomy

The word “taxonomy” is from Ancient Greek and means “a method of arrangement”. Biological organisms are classified, or arranged, into groups, called taxa, based on shared characteristics. These taxa are organized based on  how closely the organisms are related. Carlolus Linnaeus is credited with the current system of classification with his publication of Systema Naturae in 1758. 

Linnaean taxonomy uses a system known as binomial nomenclature to give names to organisms. All living organisms are assigned a name with two parts: a generic name (genus) and a specific name (species). Based on the genus, the organism is given a taxonomic rank on where it fits into an ancestral hierarchy. From most broad to most specific, the seven taxonomic categories for plants are: domain, kingdom, division, order, family, genus, and species. For example, under this system, Phalaenopsis schilleriana would be classified as: Eukaryota, Plantae, Magnoliophyta/Angiospermae, Asparagales, Orchidaceae, Phalaenopsis, schilleriana

In 1901, a second method of classifying organisms, called cladistics, appeared in a work written by Peter Mitchell. Cladistics proposes that organisms should be classified based on their most recent ancestry. In Ancient Greek, a clade means a “branch” and is defined as a grouping that contains a single common ancestor and all the descendants under that ancestor. With the invention of genetic analysis and its increasingly affordable cost, organisms are being reclassified into their appropriate clades.  So, Phalaenopsis schilleriana is now classified as: Plantae (Kingdom), Tracheophytes (Clade), Angiosperms (Clade), Monocots (Clade), Asparagales (Order), Orchidaceae (Family), Epidendroideae (Sub-family), Phalaenopsis (genus), schilleriana (species). For a discussion on clades, see “What is a Clade Anyway” by Wesley Higgins, published in the September 2020 Orchids magazine.

One of the problems in understanding this topic stems from the fact that the field of Taxonomy itself has evolved over the years. An article entitled, “The Taxonomists’ Dilemma or the Evolution of Taxonomy” appeared in a December 1967 American Orchid Society Bulletin:

“When Linnaeus first devised his system of nomenclature he was trying to put species with common attributes in the same genus, thereby mirroring in the names the similarities in structure. This, of course, resulted in a certain amount of order where little had existed before…. Linnaeus and most other scientists up to 1859 (and a good many for some years after that) thought of each species as being separately created. With Darwin’s publication of The Origin of Species there gradually came a change in this basic concept but its impact on taxonomy was slow to come, having to wait for the development of genetics and its outgrowth – population genetics.” – Henry M. Wallbrunn

Additionally, taxonomy is complicated because the initial Linnaean classification system was based on physical characteristics (morphology), habitat, and behavior and had an inherent flaw in that organisms can share characteristics, but not necessarily be descended from the same ancestor. For example, many orchids use mimicry to attract pollinators or have similar-shaped leaves or flowers.

In recent years, DNA analysis of organisms has allowed scientists to more accurately classify organisms based on their genetic makeup which has supported the cladistic system of classification. This has led to many organisms being “reclassified” into their correct genus and species. However, using genetics to classify organisms is also not perfect and may result in multiple reclassifications. Part of the problem is defining at which point of difference in genes is an organism distinct enough to be considered a separate genus or  species. This is somewhat arbitrarily done. Most scientists consider a 5% difference in selected genes to be enough to declare a new species. However, this is not a universal rule. Further reading on taxonomic changes can be found in "Why Genus Names Change" by Andre Schuiteman, Orchids 92(2):118-123. 

Another pitfall in defining species and relatedness is interbreedability, or the ability of certain plants that are distantly related to successfully breed and produce viable offspring. The Cattleya alliance is a great example of this. Laelia, Cattleya and Brassavola are all interbreedable and produce viable offspring, even though they are not closely related and might be found in totally different environments.

Orchids have not been immune to this reclassification, so much so that regular updates are provided by Plants of the World Online (https://powo.science.kew.org/), an international collaborative program managed by the Royal Botanical Gardens, the authoritative source for changes in plant nomenclature. This is why an orchid you are familiar with may now have a new name. The following is a list of the most recent taxonomic changes to the Orchidaceae Family.

Orchid Nomenclature

Ever wonder what those names and letters on your orchid tag actually mean? This is another area where taxonomic changes can have an effect. Click here to see a simplified explanation of some of the common name and letter combinations you may find on your orchid’s tag.