Saturday, February 22, 2014

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 mediaMuch 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:

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:

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

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