Why some plants have multiple scientific names

Carolus Linnaeus (1707-1778), originated scientific names as we use them today. Earlier naturalists used Latin descriptions of species: Linnaeus assigned each species a two word name. The first word in the name is the genus, the second the species within the genus. After over two centuries we continue to use Linnaeus' system. And in Systema Naturae, first published in 1735 and revised and expanded until 1770, Linnaeus originated the now familiar hierarchy with kingdom at the top and species at the bottom. In recognition of this work, Linnaeus is sometimes called the "Father of Taxonomy." Taxonomy is the science of classification.

Linnaeus also began the practice of placing the name of the first scientist to describe the plant after the species name. For example, the common Pokeweed is Phytolacca americana L. In this case the L means that Linnaeus himself classified and named the plant. As the progenitor of the system, Linnaeus described, classified amd named thousands of plants. So you will see the L. many times. Sometimes a second botanist would also describe and name the same plant, unaware of the earlier name. Or perhaps the plant has a variable growth habit, and the second botanist thought it was a new species. So then there were two names for the same species. Then a third botanist could decide that he had found a new species and give the same species a third name. Some very common plants have been given several scientific names over the past two centuries.

The common Pokeweed, found across most of North America, is a good example. More than a century after Linnaeus named Phytolacca americana, J. S. Small decided that he had identified a second species: Phytolacca rigida. So there was a new species which was refered to as Phytolacca rigida Small. Currently the two are considered one species, Phytolacca americana; rigida is considered a variety of the species. Today it would probably be referred to as Phytolacca americana var rigida Small. The "var" indicates a variety (what we used to call a subspecies): "Small" is the scientist who described it.

When looking at a plant with more than one scientific name, taxonomists try to maintain order in the system by following a set of rules. One rule is that the earliest valid name is the name that will be conserved, or kept. This is a reasonable idea, but sometimes confusing in practice. A scientific name may have been accepted and appeared in books for decades. Then someone finds that there was actually and older name which had never been used, perhaps because it was in an obscure publication. In that case the older and unfamiliar name may be conserved, and the newer but better known name discarded. Field guides and reference books suddenly have an obsolete scientific name for the plant.

This hints at another issue. Often it is not at all clear where the line between different species should be drawn. One scientist may see two distinct species of a plant while another may see two varieties of the same species. The first is called a "splitter" and the second a "lumper." And even if a consensus is reached about a particular plant, its status may be reconsidered when new lines of research (DNA, for example) are available.

Common Blue Violet is example. It is as abundant as the name suggests. But determining the scientific name of such a common and well known plant is not so easy as one would suppose. Field Guides may list it as Viola floridana, or as Viola papilionacea, or as Viola palmata. However, if you consult the ITIS (Integrated Taxonomic Information System) site for North America, you will find it listed as Viola sororia: you will also find thirteen other scientific names which have been superceded, including the names I have listed.

The Roundleaf Bluet is another plant with multiple names still in current books. Depending on which field guide you use, it may be listed as Houstonia procumbens or as Hedyotis procumbens. And should you delve into older texts you may encounter Anotis rotundifolia, Oldenlandia rotundifolia , Panetos rotundifolius , Hedyotis rotundifolia, or Houstonia rotundifolia: all referring to the the same tiny plant. In particular, as older books are digitized and made available online, the obsolete names can be confusing to the unwary.

As a matter of fact, we are in the middle of a vigorous reshuffling not only of species but of entire genera. Joe-pye Weed is found across most of Eastern North America. For well over a century it has been known as Eupatorium fistulosum. In recent years there has been an effort to move it to a new genus Eupatoriadelphus and name it Eupatoriadelphus fistulosus. At this time (2009) a visitor at the USDA (United States Department of Agriculture) site will find it listed as Eupatoriadelphus fistulosus: however the ITIS lists it as Eupatorium fistulosum.

This stuff is not especially important to most wildflower lovers, but if multiple field guides or web sites are consulted, it helps to know that a given species may have had multiple scientific names. Botanists use the word "synonym" for another scientific name, outdated or questionable, for a species in addition to the accepted name. A visit to the ITIS site will often turn up several synonyms for a common species.

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