Navigating the Herbarium

Plant Names

We thank Carl Linnaeus, a Swedish botanist working in the mid 18th century—just about the time of the American Revolutionary War—for our ingenious system for naming organisms. "Binomial nomenclature" provides every species with a unique two-part name that we often refer to as a "binomial" or "scientific name."

The first part of a scientific name is the genus (plural: genera), which means "kind" in the sense of "category" in Latin. Our best-known genera have names derived from Latin words: Rosa means "rose," Canis means "dog," and Quercus means "oak" in Latin.

The second part, the specific epithet, often acts as an adjective that describes the genus. Quercus rubra, the scientific name for the red oak means "red oak;" rubra means "red" in Latin. Quercus alba, is the scientific name for white oak, and yes, alba means "white" in Latin.

Because many plants were (and still are!) discovered independently by more than one person and given different names, botanists keep track of the "author" of each name. The "true" or "legitimate" name is awarded to the botanist who first named and published a description of the species, following a strict set of rules. This system is known as priority. The first time a plant binomial appears in a document, the author must be included. The names of important botanists have official abbreviations. "L." stands for Linnaeus.

The International Plant Names Index (IPNI) is an online database that lists all the plant binomials, their authors, and publication information. The site is a collaborative effort among the Royal Botanic Gardens, Kew, the Harvard University Herbaria, and the Australian National Herbarium.

Type Specimens

When botanists name a plant they use a concept that dates back to Plato called typification. Plato felt that for everything in the universe, there is, somewhere, an ideal form of that thing. Each binomial has its own unique, ideal "type specimen." Today, when a botanist names a plant, he or she must also prepare a type specimen (the holotype) and a series of isotypes, which are specimens collected at the same time and place as the holotype. Isotypes serve as back-ups and each one is stored at a different herbarium. If the holotype is destroyed, an isotype can take its place. 

This may seem like a lot of work…and it is. But botanists learned a hard lesson during World War II when bombing raids destroyed the herbarium that housed many of Linneaus's unique and irreplaceable type specimens.

Here's the one-and-only type specimen for the name Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg. (Note that more than one author was involved in the naming of this plant.) This is the South American rubber tree that provides you with your steel-belted radials. This type is stored at the Fielding-Druce Herbarium in Oxford, England.

Voucher Specimens

Whenever anyone performs any kind of botanical work including ecological studies, DNA analyses, a floristic survey, assays for plant chemicals with medicinal properties, etc., a voucher specimen of the plants in question should be prepared and submitted to a herbarium. The location of the specimens and their numbers should be published with the results of the studies.

This very important step is often neglected. Why is it important? Voucher specimens serve as guarantees that the plants in the study were correctly identified. Without vouchers there is no way to know whether researchers really studied the plants they said they did.

Sometimes, years after an investigation, taxonomists decide to "split" a species (that is, recognize two or more new species where we once considered only one) or "lump" two or more species (that is, decide that two or more species really should be recognized as one). A voucher specimen is invaluable, especially in cases of splitting, because taxonomists will know exactly which of the two (or more) new species was under investigation.

Classification System

After a plant is named, it must also be classified. This means organizing it into a hierarchy of related groups. People use hierarchical classification systems every day. Here’s an example: You live at an address on a particular street; that street is in a town or city; that city is in a county; that county is in a state; the state is in a nation; the nation is on a continent, and the continent is on planet Earth. Moving through the "levels" from address number to planet, one passes through ever more-inclusive categories.

At any given level, members of that level are "more closely-related" to each other than they are to members of another group at the same level. For instance: all the streets in Mankato can be considered "more closely related" to each other than they are to any street in New Ulm. However, if we step up to the state level, we could say that streets in Mankato and streets in New Ulm are more closely related to each other than they are to any street in Allentown, Pennsylvania.

Our biological classification system makes the same assumption. At any level within the classification system, members of that group are more closely-related to each other – just like you’re more closely-related to members of your family. We refer to these levels as taxa (singular: taxon). From most inclusive (includes the most species) to least inclusive (includes the fewest species) the taxa in our classification system are: Domain, Kingdom, Phylum (plural: phyla), Class, Order, Family, Genus (plural: genera), and Species (same for plural as singular).

Taxonomic Keys

A taxonomic key, also known as a dichotomous key, allows people to identify species. At each step the user is given a choice between two alternative descriptions. Paired descriptions are given the same number and indentation on the page; they are referred to as couplets. Like following paths through the woods, one comes upon a fork and must choose to follow one branch or the other based on which description in the couplet most closely-resembles your species. Eventually, you will be led to its name.

Practice using a taxonomic key: Click here to download a [PDF] key to common vegetables (16 KiB).

Botanical terminology can be challenging. Search an on-line glossary developed by the authors of the Flora of North America project.

Systematics

"Systematics" and "taxonomy" are disciplines within biology. Historically the terms have been used interchangeably. Today we define Systematics as a broad discipline that contains three components: taxonomy, the study of the process of evolution, and the study of phylogeny.

Taxonomy includes identifying, naming and classifying species. The study of the process of evolution looks at how species develop. The study of phylogeny includes determining the evolutionary relationships among species—creating a family tree of ancestor and descendent species. Visit the Tree of Life for more information on this fascinating endeavor.

MNSU offers a course in systematics called Flora of Minnesota (BIOL 442). Students learn to use taxonomic keys to identify plants. The course is taught in alternate Fall semesters and is open to anyone (no prerequisites).