The Plant List: The First Comprehensive Inventory of Most Known Plant Species

“If the names are unknown, knowledge of the things also perishes.”¹ –Carl Linnaeus

A single plant can be given multiple scientific names over time.² More than 3,000 scientific names exist for only 19 species of Mentha, for example, and thousands of additional plants have multiple names (A. Tucker, e-mail, September 25, 2010). This is the result of plant systematists disagreeing with the original author’s naming, an unawareness that particular plants have already been named, or changing plant names to reflect evolving knowledge of relationships among plant species. Based on the widely used “principle of priority,” the “correct” name of a species should be the first name published according to guidelines set out in the International Code of Botanical Nomenclature.³ Often, the oldest plant names are found in the 1753 book Species Plantarum written by Carl Linnaeus, a Swedish botanist who is referred to as the father of taxonomy.

Still, these numerous names continue to cause confusion and problems, especially in the case of geographically widespread plants and commercially used plants like medicinal herbs. “We need clear, definitive names to facilitate communication among plant scientists and those in the commercial world, to be sure that we are all using the same name in the same way,” said John Wiersema, a botanist at the US National Germplasm Resources Laboratory and director of the GRIN (Germplasm Resources Information Network) database (e-mail, October 28, 1010). “Any piece of information on a particular taxon is largely meaningless if the name to which it is associated cannot be accurately represented.”

Seeking to solve this problem, the Royal Botanic Gardens, Kew, and the Missouri Botanical Garden (MOBOT) are currently creating a more definitive and comprehensive list of plant names that indicates which names are accepted as correct and which are synonyms.⁴ “The Plant List,” as the project is called, was started by Kew and MOBOT in 2008 as an initiative addressing the Global Strategy for Plant Conservation’s (GSPC) first target goal, which calls for “a working list of all known plant species” by 2010. According to GSPC’s website, such a list “is considered to be a fundamental requirement for plant conservation.”⁵ The GSPC was enacted in 2002 by the Convention on Biological Diversity, an international treaty that aims to stop the “continuing loss” of the earth’s plant diversity, as well as to encourage sustainable use and benefit sharing of plants.⁶

Botanists and other scientists, as well as information technology specialists at Kew and MOBOT have been developing and testing a new process to generate the list, which consists of merging existing resources through an automated, rules-based approach.⁴ The heuristic informatics method captures taxonomic knowledge into a rulebase, and computers are then used to aid in sorting out the millions of plant name records from Tropicos, Kew’s World Checklist of Selected Plant Families, The International Compositae [daisy family] Alliance, International Legume [Fabaceae] Database and Information Service (ILDIS), and plant name information from the International Plant Name Index (IPNI).

Several media sources have reported that the project will eventually cut the global list of plant names by 600,000, making the number of plant species names about 400,000.⁷ The project is not exactly cutting plant names from existence, however. “The significance of the Plant List,” said a Kew spokesperson, “is not to provide a few names and delete the non-current ones, but rather to identify the names which are used and have been used in the past, and as far as possible link the names which refer to the same species to facilitate information retrieval and study” (B. Friedlander, e-mail, October 29, 2010).

“There are around 1,000,000 Latin names for plant species,” said the spokesperson. “The estimates for the number of [actual] plant species vary from around 250,000 to 440,000. Our work on the Plant List to date suggests that the number of species is likely to be nearer the high end of that range. Thus plants have on average between 2 and 3 names; plants which are widespread and used tend to have several synonyms. This obviously is a problem. Some work we have done at Kew suggests that if you search online resources for a medicinal or nutritional plant using just one of the alternative names of a species, you might only find 20% of the information about the species. The point of the Plant List is to alert people that more than one name for a species might exist and if they are interested in finding out about that species, they need to search using the alternative names (synonyms).”

According to the Kew spokesperson, who noted that the project is still a work in progress, the list currently contains 301,000 accepted species names, 480,000 synonym names, and 240,000 remain un-assessed as being either accepted or synonyms. Remaining work includes the adding of important data sets to the resource, such as key names resources on legumes, composites, and grasses, so that the working list is as comprehensive as possible.⁴ Kew recognizes that the list has its limitations, including a lack of coverage of ferns and fern allies (pteridophytes, about 10,000 species) and algae (about 30,000 known species), variable completeness and accuracy in synonymy information for flowering plants other than monocots, and weak coverage of Southeast Asia and genera that start with letters in the latter half of the alphabet.

“It will not be perfect, but for the first time we will concentrate the available information in one place,” said the spokesperson. “One of the reasons this has not been done before is that different sources of synonymy information sometimes conflict and these differences need to be resolved.” The final list is set to be published online sometime between the 2010 winter holidays and New Year.

Though Kew and MOBOT did not work with the American Herbal Products Association (AHPA), which publishes the smaller subset of common and Latin names of most herbs used in commerce in the United States, Herbs of Commerce, 2^nd edition, this will not affect the quality of the final product, said Michael McGuffin, AHPA’s president (e-mail, October 25, 2010). “The institutions involved are highly authoritative,” he said, “and there is every reason to believe that they will produce an excellent and comprehensive final product.” Still, Herbs of Commerce will remain as is. “The KEW/MOBOT project appears to be of a very broad scope,” he continued. “The purpose of Herbs of Commerce seeks to provide a unified nomenclature for just over 2,000 herbs used in dietary supplements. These decisions were made on a case-by-case basis, usually deciding in favor of names that reflected or facilitated common use.”

Likewise, GRIN will continue to base its plant classifications on primary sources, such as taxonomic articles published in scientific literature, and will use secondary sources, such as The Plant List, “only when more primary sources of information are lacking, or perhaps to alert us to the need to further evaluate a particular taxon,” said Wiersema. Though there has been no organized effort similar to The Plant List between GRIN and its partners, taxonomic experts from these organizations continuously try to indicate and employ the most “correct” and current taxonomic acceptance of any name, he continued. According to Wiersema, the resources being used for The Plant List, which have been critically reviewed by taxonomic specialists for certain groups, will be adequate for some plant families. “For many other families this remains to be seen,” he added. A reviewer of this article noted that, while The Plant List will be imperfect, a list with errors and omissions is a better starting place than no list at all and that the manpower and funding to create a totally complete list of all names do not exist.

Before Linnaeus published Species Plantarum, biologists used various naming practices, which often included long series of Latin names, such as one of the pre-Linnaean names for the common briar—Rosa sylvestris alba cum rubore, folio glabro.⁸ Additionally, these names could be altered whenever a biologist wanted to do so. About this time, many new botanical and animal specimens were being brought back to Europe from the New World, further increasing the need for a more definitive and organized nomenclature system.

In Species Plantarum, Linnaeus introduced the binomial system of scientific naming by combining the genus name and the specific, descriptive epithet designating the species. For example, the scientific binomial of garlic is written as Allium sativum, Allium being the genus, sativum being the epithet, and Allium sativum being the species. Thus his name for common briar became Rosa canina. Though this system has been used throughout much of history, it was not until 1930 that international representatives officially agreed upon using it and Species Plantarum as the source for oldest botanical names.⁹ Among additional requirements laid out in this agreement—the International Code of Botanical Nomenclature—is the rule that to be official, botanical names must be published in a normal botanical publication that is delivered to at least 2 botanical organizations.

—Lindsay Stafford

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