tree-logo.gif (7741 bytes) Plant Taxonomy (BIOL308)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321;;


I. What is a Plant? A Traditional View

A.  Plants are characterized by their features or characters & character states

B.  Plant character states 

C.  Diversity - There are many kinds of plants including mosses, liverworts, hornworts and the tracheophytes.  Tracheophytes are vascular plants, such as ferns, horsetails, flowering plants (= angiosperms) and conifers (=gymnosperms). 

II. Taxonomy & Systematics

A.  Taxonomy
    The study of plant classification.  Classification is putting objects into groups (such as the Linnean hierarchy below).  Classification involves/requires naming (nomenclature), describing (assigning features to a taxon), and identifying (determining that an unknown element is identical to a known one) species. Another definition of taxonomy that I like is that taxonomy is the science of documenting biodiversity (Keogh, 1995).  The term taxonomy was originally coined by Augustin Pyramus de Candolle in 1813 (Stuessy; 1990, 1994).

B.   Linnaeus - "founder of plant taxonomy."  Credited with binomial system and classification hierarchy.  You likely remember the scheme (in descending order with an example).  Note:  (a) each level or unit is called a taxon (pl - taxa); (b) standardized endings; (c) kingdom is most inclusive group, species is least inclusive; (d) rank refers to level in hierarchy; (e) mnemonic device - King David Cried Oh for Goodness Sake; (f) Division = Phylum.  Caveat - in the future, the Linnaean hierarchy may vanish as new data make these groupings obsolete.

Kingdom   Division  Class  Order  Family  Genus species
Plantae Magnoliophyta (angiosperms) Magnoliopsida (eudicots) Asterales Asteraceae Taraxacum T. officinale

C.  Domains - recent work suggests that there are three major "life forms" - prokaryotes, Archaea bacteria, and eukaryotes - and these should be classified as a domain.

D.  Systematics
    The study of the diversity and the history of organisms and the evolutionary relationships between them. This term can be traced to at least Linnaeus in 1737 (see Stuessy, 1990). Our text succinctly defines systematics as the "science of organismal diversity." Note that the underlying assumption is that evolution occurred in the past and it is continuing today. Thus, the two primary goals of a systematist are: (i) to discover the nature of the evolutionary tree of life. Or to put it another way, systematics strives to uncover the "phylogeny", or evolutionary history, of a particular group of species; and then (ii) to convey this information in a classification. 

E.  Taxonomy vs. Systematics
    A fine line of distinction. These terms are often used interchangeably (as I do). However, others (purists) use "taxonomy" to refer specifically to the methods and the principles of classification (including naming & describing). Systematics (also called "biosystematics") is then used in a broader sense to include (1) taxonomy (naming, describing, identifying, classifying); (2) studies of evolutionary processes (such as hybridization, sources of variability, degree of variation in populations, reproductive isolation, origin of species); and (3) studies of phylogeny (the evolutionary relationships between groups).   

    As an aside, the first portion of the semester will focus on the activities that are traditionally considered "taxonomy" when we learn: (1) techniques to collect plants; (2) how to describe a plant using technical terminology; (3) methods to identify plants; (4) how plants are named, and (5) characteristics of plant families. During the second portion of the semester we will focus on systematics when we learn about methods of classification and how evolutionary relationships between plants are deduced.

    How well you can distinguish between taxonomy and systematics?  Click here

F. Alpha vs. beta
    alpha taxonomy refers to the more traditional methods of classification while beta taxonomy refers to more recent experimental methods.

G.  Some examples
    (a) Stuessy (1990) is a good overall reference, and he has prepared a good diagram to represent the relationship of taxonomy and systematics. (b) Walters and Keil (1996) use a silverware example to demonstrate identification, nomenclature, classification, and even evolution and phylogeny (for example, it is easy to imagine the evolutionary processes by which, say a cocktail fork, "evolved" from a dinner fork).

H.  Take-home-lesson
    This course, Plant Taxonomy, could also be called "Plant Systematics" or "Systematic Botany."  Which title do you prefer?

III.  What is a Plant? The Evolutionary View - plants are characterized by their shared ancestors, shared common ancestry.  As a result, some photosynthetic organisms are no longer considered plants.

  1. Phylogeny - represented with cladogram
  2. Overview - node, speciation event, roots, clade, sister groups, apopmorphy, pleisiomorphy, monophyletic, polyphyletic
  3. Cladogram of plants

IV. So, what does a taxonomist do? Or, in other words, what kinds of questions do plant taxonomists study? They study questions such as:

V. Is taxonomy/systematics important?  You betcha, because taxonomic information:

A.  enhances our understanding about other species and provides a method for cataloging this information
    This is especially critical for species threatened with extinction. Who better than taxonomists should speak out for the preservation of biodiversity?  In fact, taxonomists offer our greatest defense against the loss of global biodiversity (Savage, 1995; Simpson & Cracraft, 1995);

B.  enhances our understanding of evolution, evolutionary processes and biology (in general)
    Two examples from Judd et al.:  (a) Silverswords (Asteraceae) in Hawaii - incredible diversity of form & habitat, adaptive radiation of ancestor from mainland, studies show that the transition from wet
dry occurred several times; (b) Southern beech (Notofagus) - are distributed in New Zealand and southern South America.  taxonomic studies can help explain this distribution (biogeography) and the date of divergences (ca. 80 mya);

C.  has predictive value
    For example, if two plants are related (i.e., in the same genus) and one of the plants is a source of food or drug, there is a reasonable chance the other will, too. Here are a few examples of the predictive value of taxonomy:

  1. Consider taxol, an alkaloid that was first isolated from the bark of the Pacific yew (Taxus brevifolia) that is being used to treat breast cancer. It received FDA approval for this purpose in April '94 (the FDA approved the drug for the treatment of  ovarian cancer in December '92).  Unfortunately, the bark of about 3 trees is required to treat a single patient. In fact, 16,000 pounds of bark is used to produce 2.2 pounds of taxol. It is administered in a 5% saline solution. Until relatively recently, taxol was thought to only occur in this one species. A thorough search has shown that taxol also occurs in other species (which from a practical perspective will make this potential medicine more readily available). Not surprisingly, taxol was found in related species of Taxus, and in some cases, in even higher concentration than the original species. As an interesting aside, a fungus (Taxomyces andryanae) that uses yew as a host seems to be an even better source of taxol than the yew itself (isn't nature grand?). The toxicity of yew has been known since at least the time of Julius Caesar.  The plants produce a series of alkaloids including taxines and taxanines.  Taxol acts by promoting microtubule assembly and causes tubulin to polymerize.  For more information about the taxol story, read some of the references cited.
  2. Consider the anticancer drug that was extracted from a small population of Maytenus buchananii growing in Kenya. Further studies on the compound couldn’t be done because the population was too small to collect any more, but based on its phylogeny a taxonomist predicted that Maytenus rothiana in India would have the desired compound. It did (Miller and Rossman, 1995).
  3. Consider cortisone that was original found in Dioscorea.   Subsequent studies have found it in other species.

D.  has practical value (= what's edible, poisonous, medicinal)
     Useful to develop economic resources. How about some examples?  In addition to the examples cited above, 

  1. Consider, in 1987 a species of Calophyllum was collected in northern Borneo. In tests at the National Cancer Institute an extract blocked replication of HIV-1. A team returned to Borneo to collect more but found the tree had been cut down. Other individuals in the area were collected and tested by NCI but showed little activity. A taxonomist was called in and after studying the specimens showed that the original specimen was C. lanigerum var. austrocoriaceum but the recent inactive collections were C. teysmannii var. inophylloide. With this information in hand C. lanigerum was obtained from the Singapore Botanical Garden, the active compound isolated, synthesized and the drug has begun clinical trials (ASPT Newsletter 11: 2 (1997)).
  2. Consider the mealy bug (Phenococcus manihoti) that was destroying West African cassava plantations to the tune of $1.4 billion. Presumed parasites of the mealy bug were located in South America and released in Africa with no effect. A taxonomist studied the mealy bugs realized that the introduced parasites were from a different species. Specific parasites to P. manihoti were successfully introduced (Miller and Rossman, 1995).
  3. Consider the unsuccessful malaria control campaign in Trinidad in 1940. Swamps were sprayed and drained to kill the presumed vector, Anopheles albimanus, the primary mosquito vector in Latin America. But, the real vector in Trinidad was A. bellator that breeds in bromeliads growing on palms (Davis, 1995).

E.  human social impact
Believe it or not, taxonomy has implications for human societal interactions by showing "...that each species is uniquely different from every other species and thus irreplaceable, the student of evolution has taught us a reverence for every single product of evolution, one of the of the important components of conservation thinking. By stressing the importance of the individual, by developing and applying population thinking, by giving us a reverence for the diversity of nature, systematic and evolutionary biology have supplied a dimension to human conceptualization which had been largely ignored, if not denied, by the physical sciences. And yet it is a component which is crucial for the well being of human society and for any planning of the future of mankind."  And, systematics can even help us to formulate questions and answers about our own origins (i.e., "Hey Mom, where did I come from?") (Stuessy,1990).

VI. Taxonomic revival?
    During the last decade or so, the "gene jockeys" have become the scientific "power brokers" while taxonomists have been viewed as archaic "postage stamp collectors."  Many academic departments have essentially ignored the taxonomic sciences. As evidence, an analysis of papers published from 1969 to 1996 showed that taxonomy was growing through 1988 but is now static or gradually declining (Winston & Metzger, 1998).

    This is especially problematic considering the acknowledged biological crises (i.e., extinction, habitat loss) we are facing (Keogh, 1995; Fussey, 1995; Salopek, 1996). Fortunately, there has been a resurgence of interest in systematic botany (see references).  As we all know so well, "money talks."  This is also true in science. The recent funding programs (i.e., NSF program in Systematic Botany; Systematics Agenda 2000 that recognize the need to catalog biodiversity) are further evidence of the renewed interest in taxonomy.

     Recognizing the need to document diversity before it's too late, there have been several recent "all-taxa biological inventories" have been conducted (e.g., Costa Rica, Smoky Mountains National Park, Biological Diversity in National Parks, Point Reyes National Seashore) and recently a "Species Day" or "BioBlitz" was held here in Minnesota.

VII. Systematics as a Science

  1. Systematics is a descriptive science - traditional approach, similar to astronomy and anatomy.
  2. Systematics is also an experimental science - newest paradigm; hypotheses about the relatedness of plants are developed and then tested by analyzing data.
  3. Systematics is the First Science! Our ancestors were great taxonomists - they had to be in order to survive. They collected foods, medicines, etc. from the wild. In the not too distant past, botany was one of the major subjects in school. Sadly, the more "civilized" we've become, the further from our roots that we've grown.

Further Reading:

Further Study:  Check out the "quiz" and "study guide" questions

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Last updated:  08/29/2008 / � Copyright by SG Saupe