Integrative Biology 335 — Taxonomic Hierarchy

Page 21 in Class Notes

There is an incredible diversity of life on the planet earth; see the pie chart. It is estimated that there are 280,000 or more species of flowering plants. [A recent article estimated that there are about 422,000 species of flowering plants.] No one person could possibly remember all of these. It is necessary to organize this diversity into a classification scheme to communicate with others about plants. The classification system that has been most useful to biologists is one that groups related plants together into a series of hierarchical categories, so that very closely allied plants are placed together, plants somewhat related are grouped near each other, and plants that have very little in common with each other are placed far apart. Below are estimates of the number of species described thus far (which represent only a small fraction of the actual numbers).

"The first indispensable requisite is a thorough knowledge of the natural order – an intelligently conducted natural history survey. Without the general knowledge which such a survey would give us, all our measures must be empirical, temporary, uncertain, and often dangerous." — Stephen A. Forbes, Founder of the Illinois Natural History Survey

[Here is an example of a hierarchical system - the way files are stored on a computer.]

Here is an example of a hierarchial system for the group of animals that includes humans.

Chordates (vertebrates + animals with notocords)

Now that you know what a “Great Ape” is, click here .

Here is this example with the names of the categories.

Phylum – Chordata

In this class, we will be only concerned with Flowering Plants

<Diagram of Plant Phylogeny>

<Hierarchial Classification for Aster tenuifolius>

Division – Magnoliophyta [Anthophyta] – flowering plants

Division – Magnoliophyta [Anthophyta] – flowering plants

    Class – Magnoliopsida – [Dicotyledonae]
      Subclass – Rosidae
        Order – Fabales
          Family – Fabaceae
            Genus – Glycine
              Species – Glycine max

Division – Magnoliophyta [Anthophyta] – flowering plants

    Class–Liliopsida – [Monocotyledonae]
      Subclass – Commelinidae
        Order – Cyperales
          Family – Poaceae
            Genus – Zea
              Species – Zea mays

In the system of classification that we use in IB335,

Division Magnoliophyta = Flowering Plants

Class Magnoliopsida = Dicotyledons

Class Liliopsida = Monocotyledons

The plural of “genus” is “genera”

“Species” is both singular and plural.

“Specie” means gold or silver rather than paper money.

This is a HIERARCHICAL SYSTEM of classification. Names above the rank of GENUS are single words and are based upon the name of an included genus. Each rank has a distinctive ending (suffix) that is attached to the stem of the name of the genus.

The word TAXON is used to refer to a taxonomic category of any rank. The plural is TAXA.

This semester we will use subclasses to organize the lectures, since this category is used extensively in the system of classification developed by Arthur Cronquist.

A major part of this course is learning the features of a selected number of plant families. Cronquist recognizes 318 families of flowering plants; in this class, we will cover 40–50 of the most common, widespread, and important families.

There is more information on the taxonomic hierarchy at this site at Texas A&M University

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