Plant Taxonomy (BIOL308) - Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe/ |
AN INTRODUCTION TO PLANT TAXONOMY
I. What is a Plant? A Traditional View
A.
Plants are characterized by their features or characters & character statesB. 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.
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:
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,
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
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