One would think that the concept of a species would be firmly rooted two centuries after Carolus Linnaeus set forth the principles in Species Plantarum.
A lot of rules have been developed over the years for defining a species. Take for instance, the poppy family and the bleeding heart family, both of which contain many species. Using DNA, botanists discovered that several species of poppies were more closely related to the bleeding hearts than they were to other species of poppies. But they don’t resemble the bleeding hearts very much. The solution was to change the whole lot of them to the poppy family, but keep the bleeding hearts as a subfamily.
The people who make these sort of decisions are called taxonomists. They make rules about taxa (species and subspecies). In botany the rules are set forth as the International Code of Botanical Nomenclature, or ICBN.
There are even rules for breaking the rules. For example, the name for a species must follow the ICBN rules. Except plants named by Constantine Samuel Rafinesque-Schmaltz may violate the rules.
Personally, the most vexing rules are ones that allow for ambiguous names. Taxonomists are a conservative lot, and so rather than dispense with the old names, new rules are just glommed on so that both names can be correct.
For example, the second part of a species name is never capitalized. Except the species name may be capitalized if it is named after a person. Picayune. Key word may.
It is important to understand that ambiguity is inherent in Botany. Under the rules of the ICBN, two different names can both refer to the same taxon:
ICBN Article 26.2: The first valid publication of a name of an infraspecific taxon that does not include the type of the adopted, legitimate name of the species automatically establishes the corresponding autonym.
Under another set of ICBN rules, in naming a new subspecific entity, this automatically establishes the subspecies containing the type of the species. This includes cases when the type was originally named as a variety.
But, but, but… if a validly named taxon contains infraspecies, then the names will be a mix of explicit and implicit subspecies, which may or may not also have varieties.
The remainder of this document is filed under the category of “who gives a rat’s ass”, because as it turns out, taxonomists do. Here for your infinite pleasure are the rules for naming species below the rank of species (infraspecies) in botany.
Let’s just start with the concept before invoking the rules. Concept: When a species of plant varies its appearance over relatively short distances, these are referred to as varieties. Where several varieties are recognized within a species, they may be grouped within a subspecies.
This concept depends on what one defines as “relatively short distances”. This concept is not explicit about the rationale for when the use of subspecific rank would be justified, and hence different authors have been inconsistent in its application.
In one view, Eric Hultén (1968) explicitly refers to the use of the subspecies category for, “… populations occupying large and partially or completely isolated geographic areas … .”
Turner and Nesom (2000) summarize a different view of the use of infraspecific botanical names. They refer to the ICBN, noting that, “… usage of these categories [variety vs. subspecies] remains inconsistent and commonly without explicit rationale.” They emphasize that, “Philosophical and interpretive differences regarding use of infra-taxon categories are magnified by this tension in the ICBN: variety and/or forma are the ranks to be used first in describing infraspecific taxa (Article 4.1), but subspecies is the term first in hierarchical rank below species (Article 4.2).”
ICBN Article 4.2 clarifies that use of the “sub” prefix provides added ranks.
ICBN Article 2.1 states: “Every individual plant is treated as belonging to an indefinite number of taxa of consecutively subordinate rank, among which the rank of species (species) is basic.”
ICBN Article 4.1 states: “The secondary ranks of taxa in descending sequence are tribe (tribus) between Family and genus, section (sectio) and series (series) beween genus and species, and variety (varietas) and form (forma) below species.”
Turner and Nesom (2000) set forth a set of new varietal name combinations for Styrax platanifolius that overturned prior subspecific taxonomies, even going so far as to do away with the subspecific categories. Notably, these new names were not accepted by the Flora of North America, the Integrated Taxonomic Information System or theplantlist.org (Kew, Missouri Botanical Garden). Nice try, guys.
Other unsuccessful interpretations of infraspecific taxa have attempted to relegate variety as second in naming preference to subspecies, for instance that of Raven (1974), who proposed equating the term subspecies with variety.
In summary, while the concept of variety remains well established, we are left with a hodge-podge of different interpretations for the designation of a subspecies, somewhat akin the first example from the poppy family, except in that case, there was DNA evidence to override outward appearances, assuming one can trust DNA.
About all that can be said is that the use of geographic separation tends to be more widely accepted qualifier for subspecific designation than it does for varietal differentiation. Or, Hultén rules.
One of the fields of botany is determining the constituents of a flora, i.e., the names of all taxa that occur in a given area. Given the ambiguity in naming conventions, how does one go about composing a flora where each name refers to a unique taxon?
Even though tedious, the making of a checklist of unique taxa can be simplified because the rules of the ICBN allow a unique determination of equivalent names to be made as follows:
(1) tetranomial names having both a subspecies and variety are superfluous and can be eliminated.
(2) taxa having mixed infraspecific ranks with the same epithet can all be relegated to varieties, or all to subspecies, provided the publication of those taxa considered all of the possible infraspecies and not just some of them.
(3) autonyms (infraspecies with the same epithet as the species name) having no other sister varieties within a flora can be eliminated with the understanding that the species refers to the variety of the same name in the strict sense (sensu stricto).
(4) Taxa with more than one infraspecies can be listed only under their infraspecific names, eliminating the need to list the parent binomial name.
Perhaps the most straightforward approach is to just ignore the infraspecific taxa and simply list the species. But for some reason, this approach is seldom practiced. Possibly this is because we are descended from vain, egotistical ape-like creatures, but without fail, every list of plants always has at least one exception where the variety or cultivar or form (Eglantine Rose!) is part of the name.
In conclusion, it is safe to say that complexity and confusion are inherent to botanical nomenclature, and those who claim to have a clear understanding are probably not very well understood. But with the growth of online floras and downloadable databases, it is possible to add to the confusion and join the ranks of the taxonomists.
Hultén, Eric. 1968. Flora of Alaska and neighboring territories: A manual of the vascular plants. Stanford Univ. Press.
Turner, B.L.; G. Nesom. 2000. Use of variety and subspecies and new varietal combinations for Styrax platanifolius (Styracaceae). Sida 19(2):257-262.
Raven, P.H. 1974. Proposal for the simplification of infraspecific terminology. Taxon 23: 828-831.