What Do Those Plant Names Keep Changing?

Many of you may have noticed that some of the plants that you finally learned the botanical name for now have different names than the ones that you spent so much time memorizing.   Why?   Because taxonomists want to keep you guessing?   No.   It is all about understanding the relationships between species.   DNA research has been incredibly helpful to taxonomists in understanding the relatedness of one species to another, and how groups of species are related to other groups.   The basic concept that one species must be derived (descended) from another is know as cladistics.   Cladistics requires that there can be only one line of parenthood, or lineage, for each and every species; that you cannot have two species of the same genus that are not genetically related.   The lineage (genealogy)/family tree must be simple, monophyletic (monophyly).   Conversely, cladistics forbids paraphyletic groups.   Since cladistics is now the model used to determine relationships between species, and higher levels of grouping (genus, family, order, etc.), lots of taxonomic reorganization has resulted as more and more DNA evidence is gathered and analyzed.

Sometimes, long-held beliefs about relatedness of one species to another is thrown out because the DNA of the two are shown to be very different, not as closely related as previously thought, and species 1 gets assigned to a different genus, or even a different family, than species 2.   Sometimes, more recent names are thrown out and older name resurrected based on the newest evidence (an earlier taxonomist had it right after all).

There are rules that govern how a species is named, and which name is considered valid, based on the International Code of Botanical Nomenclature, which is changed and adopted periodically by the International Botanical Congress.   The most recent code rules were adopted by the Eighteenth International Botanical Congress held in Vienna, Switzerland, in 2006, referred to as the Vienna Code.   ALL the rules about naming plants are addressed in this Code.   Like most regulations, they can be very complex and confusing, but the goal is to have a clear method of naming plants so that everyone knows which plant taxon is being discussed by two or more individual persons, like you and me.   The first two sentences of the Codes’ Preamble state this more clearly than I can:

“Botany requires a precise and simple system of nomenclature used by botanists in all countries, dealing on the one hand with the terms which denote the ranks of taxonomic groups or units, and on the other hand with the scientific names which are applied to the individual taxonomic groups of plants.   The purpose of giving a name to a taxonomic group is not to indicate its characters or history, but to supply a means of referring to it and to indicate its taxonomic rank.”

With that said, keeping track of a plant’s name and understanding its relationship to other plants is challenging and can be fun, and frustrating at the same time.   Below are two examples of name changes based on the Code and taxonomic research.

Isomeris arborea (Bladderpod) and Heteromeles arbutifolia (Toyon) are the two examples I wish to use for this illustration.

Isomeris arborea has a new name, Peritoma arborea. It has long been considered a member of the Capperaceae (Capper family); however, recent research has shown that Peritoma belongs in another family, Cleomaceae (Spiderflower family).   The species in the Cleomaceae and Capparaceae have been shown to be different enough, and using cladistic models, evolved separately, from other species typically associated with the Brassicaceae (Mustard family).   Apparently, the Cleomaceae and Brassicaceae are closely related to modern Capparaceae from a common ancestor in the Capperaceae.

Toyon has had a number of names too, but in this case research into the archives of botanical publication has discovered that Abrams published the name Heteromeles salicifolia Abrams using the "New York Code", parts of which were very different from the "European Code".   The New York Code was abandoned in 1930 when it was reconciled with the European Code into the first International Code (adopted in 1930).   For that reason, Abrams' Heteromeles salicifolia was no longer considered valid and Heteromeles arbutifolia (Lindley) Roemer was recognized, and used for several decades now.   The rules state that the first name published in a valid manner has precedent and is the name that should be recognized.   Lindley published the name Photinia arbutifolia in 1820.   Max Joseph Roemer published the name Heteromeles arbutifolia in 1847.   Carl Presl validly published the name Photinia salicifolia for the same plant in 1851 (apparently actually in 1849, which Abrams reclassified to Heteromeles in 1910, and Lindley’s name had precedent over Presl’s name for it, Abrams’ name became a synonym.   (Thanks to Dieter Wilken, this corrects a misunderstanding of what was printed in Volume 21, Issue 1 of the Matilija Copy, published 11 August 2010.)

Figuring this out is a detective’s job; all we need to do is “accept” the correct name.   Then we have to still remember all the other names used for the same plant because all those floras we have in our library still have the old names.   Whew!!!!

Why is it Important to Stay Current With the Taxonomy?

As explained above, the taxonomy tells us how a taxon is related to other taxa, and which ones are "unique".   That uniqueness, at least at the species level (including subspecies and varieties) is how we generally determine species richness and biodiversity in a given area, such as for Ventura or Santa Barbara Counties.   When a taxon is limited in its distribution or population numbers we consider them to be rare, sometimes so rare to have the state or federal government resource agencies formally listed them as Threatened or Endangered.

When a taxon is rare, we try to be mindful of our actions so that we do not impact it so much that we cause it to go extinct.   At least those humans that are mindful of their responsibilities as thinking beings that have the power to significantly alter their environment.   Keeping track of plant taxonomy is important in the studies of floristics and conservation biology, and for impact assessments conducted via the California Environmental Quality Act and the National Environmental Policy Act.   Examples of recent changes in plant taxonomy related to recent or current land development projects include the Newhall Ranch and Tejon Ranch developments, which are proposed to significantly impact newly recognized species, including the newly described species Helianthus inexpectus, Navarettia ojaiensis, and Gnaphalium species nova.   If the consulting botanists where not staying current on plant taxonomy, several very rare plant species would go extinct before we even knew they existed.   That is just plain unacceptable.

How do you keep track of the name changes?   That certainly can be a challenge as the changes are typically published in a scientific, peer-reviewed journal, and some of those journals are very or somewhat obsure.   Those journals are published by a society of professionals, and distributed to its members.   An example is the journal Madrono published by the California Botanical Society (not one of the obscure journals or societies - I am a member).   Regardless, we can't possibly belong to every professional society or recieve and review every journal.   A clearinghouse would certainly be helpful on this front.   While not a clearinghouse, the Jepson Herbarium gets us a long ways down the road to keeping on top of the name changes with its list of name changes since publication of the first edition of The Jepson Manual.   This list has two columns, the first listing the names included in the 1st edition and the second column listing the names to be used in the 2nd edition.   Check it out.   You may be very surprised with what you learn.   Some of the changes return old names, some rearrange taxa within a familar genus or species, and others will be entirely new.