Why Classify Plants?

In the last post, we discussed the classification of life and how it's not as simple as it seems. Since it's so difficult and confusing, why bother classifying life at all? I hope to explore in this post some of the reasons why, specifically related to plants.

First, classification is an integral part of an organized and practical naming system, which Linnaeus recognized; he closely linked classification and naming. The official names for creatures prior to his work served two functions: to identify and describe. The names were in Latin (the universal "educated" language) and could be two or more words long. The first word was the generic name for the creature and the rest of the words formed a specific description. Sounds like a pretty good idea, but since you had no limit on the number of words in the specific description, you ended up with names like: Plantago foliis ovato-lanceolatus pubescentibus, spica cylindrica, scapo tereti. Understandably, Linnaeus recognized things were getting out of hand and that no one would be able to remember these ridiculously long names. He decided that each name should still be two parts, generic and specific, but that the specific name should be limited to only one word, while the lengthier descriptions should be listed elsewhere. And so, the lengthy Latin name listed above became Plantago media. Much better. This "binomial" (two name) system of naming is still used today, and we still use Latin since it is the classical universal scientific language; each Latin name is held in common around the world, so scientists in different countries can be on the same page when it comes to names and descriptions of life forms, which would otherwise be impossible because of language differences.

Plantago media (Photo credit: Sten Porse via Wikimedia Commons)

This binomial naming system inherently incorporates classification. Plants of the same species are able to reproduce with one another "naturally" (i.e. no human intervention) in the wild and produce viable offspring (seeds that will grow). Plants with the same generic name (aka "genus") are closely related, sharing many characteristics, but they do not reproduce with one another naturally in the wild. The next broader stage of relationship is at the "family" level, which usually includes a number of different related genera (plural of "genus") that share even broader characteristics. So, a plant not only has a name as an identity; its name is an indicator of relationships with the thousands of other plants and organisms in the web of life.

A simplified taxonomic family tree I drew to show how relationship and naming go hand in hand.

These relationships are important to know because plants that are related share similar characteristics. This one fact has a number of very useful practical implications like finding sources for medicinal compounds. If you found an especially effective medicinal compound in a rare plant, you would want to see if other more common species with this same compound exist to serve as sources for the medicine until a synthetic method for production is developed (which can take many years). It is often the case that closely related plants will produce similar compounds, so classification comes in handy here. A good example of this situation is Taxol, a powerful anticancer drug. The active compound in this drug, paclitaxel, was discovered in the bark of the Pacific yew (Taxus brevifolia), which was harvested from wild trees to produce the drug from 1967 to 1993, thereby killing each tree used for this purpose.  Since the tree itself did not have a large range, the cancer-fighting drug was not widely available and the Pacific yew's future was in danger. So, scientists began to look elsewhere and discovered that the compound was also found in other species of yew trees and that needles from a common cultivated species (Taxus baccata) could be harvested and used in a semi-synthetic method of drug production, which made the medicine much more widely available and saved the Pacific yew from being harvested to extinction. Hooray for taxonomy!

A branch of Taxus brevifolia, the Pacific Yew (Photo credit: Jason Hollinger via Wikimedia Commons)

Harvesting the bark for Taxol. (Photo credit: NCI via Wikimedia Commons)

The finished product. (photo credit: drugdiscovery.com)

Another example regards avoiding poisonous plants. If you grew up with poison ivy (Toxicodendron radicans) in the north and know it is in the family Anicardiaceae, you could save yourself a lot of miserable itching by knowing which other plants are in the same family, like poisonwood (Metopium toxiferum) here in the Keys. Another plant family to learn to identify and avoid is Urticaceae, which contains many species of plants with stinging hairs. Lest you think "stinging hairs" don't sound so bad, check out the following video, which might motivate you to learn a little botany before your next trip through the woods:

Click here to watch the video on YouTube if the one above does not load.

Classification also helps with conservation efforts, as it gives us an inventory of the world's plant species and tells us how related they are to one another. This information can, for example, help us prioritize which plants to conserve. While no species should be treated as expendable, classification comes in handy if we have to choose between spending our resources to preserve, say, one of the 1,200 species of orchids in the genus Dendrobium or the species Ginkgo biloba, which is not only the only species in the genus Ginkgo, it is the only genus in the family Ginkgoaceae (compared to 880 genera of orchids in the orchid family, Orchidaceae), and is even alone in its own DIVISION (to put that into perspective, another example of a plant division is "flowering plants," which includes about 250,000 species); in short, there is nothing else like it on earth. Conservation efforts don't have unlimited funds, so if we have a good classification of plants, we can try and conserve the most diversity with the limited resources available for these efforts.

A nice specimen of Ginkgo biloba. Photo credit (from Wikimedia Commons)

The very distinctive leaves of Ginkgo biloba. (Photo credit: James Field via Wikimedia Commons)

Classification also helps when it comes to developing desired traits in plants such as higher fruit yield, disease resistance, or stress tolerance through breeding. While different species in the same genus do not reproduce naturally in the wild due to a number of factors, they will often produce viable seed if pollen from one is introduced to another by a human. To make a hybrid, you would find out which plants are closely related, then select from that group the species that have the qualities you want for breeding. For instance, if you wanted an especially tasty and disease-tolerant citrus tree, you would try to find a species of citrus with great fruit yield / taste and a related species of citrus noted for its disease resistance. Thanks to classification efforts, you can find a list of all the known citrus species in the world, and from there, you can find out which ones are tastiest and which ones have the least disease problems, then try and make some magic happen. This process has recently become very important for Florida farmers with the spread of citrus canker and citrus greening disease; hybridizations are made to produce trees with the best disease resistance and fruit quality.

Not exactly what you want to see on the grocery store shelves.

I hope this post has given you a better idea about some of the practical uses and benefits of plant classification in areas like drug discovery and development, food security, conservation, and the avoidance of painful and/or poisonous plants, which I hope will motivate you to take a closer look at those curious Latin names on our plant labels during your next visit!


Rick Hederstrom
Associate Director

Classifying Life

Humans, by nature, seem to like order: distinct entities with names that fit neatly together in relationships that make sense, like in filing cabinets and family trees. It makes sense that if humans classify everything in their own lives, they would want to do something similar with the life that surrounds them. We are a "botanic garden" and that very name involves a classification of life ("plants"). When you explore a botanic garden, you find that initial classification broken down further into more specific groups (family, genus, species) that are often indicated on display labels in front of individual plants. So how did this classification come about and how exactly does one go about classifying life, starting at the most general level?

I suspect if we were asked to organize and classify living creatures, most of us would do what was done prior to the 18th century: divide all life up first into "vegetative life" and "animal life" based on mobility and how organisms look overall. Vegetative life would include creatures like plants, algae, and fungi, while animal life would include mammals, humans, birds, fish, reptiles, insects, etc.

So where do we put this guy?  #classificationconundrums (Seriously, this is real: photo from keralitesblog.blogspot.ro)

This first division of life into Vegetative and Animal was used by Carl Linnaeus in the early 1700s when he set out to create a comprehensive classification and naming system for life on earth. One might say the classification of life first became a science at this time. He developed a hierarchical system for classification in which Vegetative and Animal were "kingdoms" with subcategories that started out general and became more and more specific (i.e. phylum, class, order, family, genus, species). His system was based mostly on reproductive characteristics, which were more reliable and accurate than using overall physical appearance and mobility as main considerations.

Carl Linnaeus' landmark work on the classification of life, Systema Naturae.

Linnaeus did a lot for the science of classification (known as "taxonomy"), but a huge amount of life, which for the most part cannot be seen with the naked eye, went unclassified in his work, even though Antonie van Leeuwenhoek discovered microorganisms in the mid- to late-1600s with the help of the advanced (at the time) microscopes he developed. Finally in 1866, a man named Ernst Haeckel took these creatures into consideration by classifying life first into three kingdoms as either Plants, Animals, or Protists (single-celled organisms and simple multicellular organisms that did not seem to fit well as either a Plant or an Animal). This was another step in the right direction, but there was still much to learn about these tiniest of life forms, which were to make a disproportionately large splash in taxonomy.

Amoebas are single-celled organisms that wound up classified as protists...you can understand the dilemma of trying to decide how to classify this sort of creature.

In the 1800s, taxonomists began to arrange life into "family trees" to reflect relationships, based on the view that all life shares a single ancestor and differentiated over time into separate species, which was not really something considered prior to 1859, when Darwin's "Origin of Species" was published.

Here's an early "tree of life" done by Haeckel. Note the three main divisions of life.

When creating these "trees," the first division of life reflected the earliest presumed differentiations, which were usually determined to be the most fundamental differences. As we mentioned earlier, the most fundamental differences in life were thought to be between plants and animals (and later, protists), but in the late 20th century, classification systems experienced dramatic restructuring based on cellular and genetic analysis of life, which was previously impossible due to technological limitations. Scientists began realizing that the differences between plants and animals were much less fundamental than originally thought, relative to other life forms on earth. Plants and animals are actually quite similar on the fundamental levels of cell makeup and genetic structure / coding:

Taxonomists today think that the difference between life with cells having DNA in a nucleus and membrane-bound organelles (specialized structures found in cells of plants, animals, and fungi) and life with free-floating DNA and no membrane-bound organelles are the most fundamental meaningful differences in life, also thought to have occurred very far back in time. We call these two forms of life prokaryotic life and eukaryotic life. Because of this, notable taxonomists like Carl Woese now think that the first division of life should be made into domains like Bacteria, Archaea, and Eukarya, which would be a level above kingdoms (plants, animals, protists, fungi, etc.), which were previously considered to be the most general classifications of life.

A diagram of Woese's three-domain classification, showing how plants, animals, and fungi are actually "close relatives" when compared to some of the other life found on earth, most of which is not readily visible.

Bacteria and Archaea do not reproduce sexually and are both single-celled prokaryotes, but they have enough significant differences in very fundamental areas (membrane structure and genetic structure, makeup, and coding) to warrant splitting into two domains. Prokaryotic life is believed to have begun on earth from 3.5 to 2.7 billion years ago, developing in the earth's early inhospitable conditions. Since the conditions of early earth are hypothesized to have been quite extreme, it is likely that organisms much like today's Archaea, which live in extreme environments such as underwater hydrothermal vents, oil deposits, and volcanic hot springs, were first to exist. Bacteria are also ancient; Cyanobacteria are the first life forms we have evidence for in the fossil record. It is the only prokaryote that uses photosynthesis to produce food and it forms the basis of most of the aquatic food chain along with algae. While it is generally agreed that prokaryotic life was the first life on earth, it is not certain if Bacteria or Archaea came first.

Archaea form the basis of deep sea hydrothermal vents, using the chemical compounds from the vents for energy.

Cyanobacteria can also tolerate some extreme conditions; they are responsible for the psychedelic colors (except the blue) of the Grand Prismatic Spring in Yellowstone National Park.

Eukaryotes appeared 2.1 to 1.6 billion years ago and may have developed when certain prokaryotic cells were "eaten" by others and rather than being digested, were put to use by the cell. These became the membrane-bound organelles like chloroplasts and mitochondria found in eukaryotic cells. Somewhere along the line, single-celled eukaryotes began to work together as groups to make multicellular organisms, eventually becoming many of the easily visible organisms we are most familiar with. It's amazing to think that "I" am actually trillions of specialized cells working together. It's not until we progress very far up the "tree of life" that we encounter humans, who are out on the tip of a far branch as relative newcomers to the planet and only a single species among thousands. Here's a beautiful diagram called the Hillis Plot, which is basically a modern "tree of life" in circle form, with humanity's position indicated in the upper-left-hand corner:

It's incredible to think that only a single species among so many thousands has had such a disproportionate impact on the planet...

...and in such a small span of time: in the "hour" of the earth's existence, humans have been around for 0.1 seconds.

I hope you've gained an appreciation of just how difficult it is to classify life, and we've only been considering the most general categories, which should be the easiest! Now just imagine making the thousands of further distinctions and categorizations in the "tree of life" on the levels of phylum, class, order, family, genus, and species that you see in the Hillis Plot... I can assure you it doesn't get easier. Classification and naming of life is certainly not cut and dry, and as much as we humans dislike disorder and chaos, life seems to resist the organized classification we would like to make for it. All that I've brought up in this post is really only the tip of the iceberg and there's good reason to believe the classification of life we currently have will look quite different a hundred years from now. Indeed, taxonomists are starting to transition from the idea of life and its history as a "tree," seeing it now more as a chronological "web" for reasons such as horizontal gene transfer.

Who knew life could be so complicated and that those two apparently innocuous questions posed in the first paragraph would require such an explanation... Go grab some ice for your brain, as I'm sure it's pretty sore after reading this post!

Sometime later, after you've recovered, I hope to discuss the classification of plants in particular and why it's so important, now that we've seen where they fit into the larger framework of natural life.


Rick Hederstrom (domain: Eukarya, kingdom: Animalia, phylum: Chordata, class: Mammalia, order: Primates, family: Hominidae, genus: Homo, species: sapiens)
Associate Director