Why classify?

When you have a lot of things to keep track of, it is helpful to have an organizing scheme.

Where do you look for cookies at the grocery store? 

How do you tell your friend where you live? 

How do you find your favorite CD at the music store?


With as many living things as there are in the world, we need a good way to keep track.


History of Plant Classification

The development of western plant taxonomy has at least five distinct periods:




·natural affinities




•People have been using plants and naming and classifying them forever, even if not written.

•Sometimes called “folk taxonomy”

•food, beverages


•building materials

•poisons (on arrows for fishing or hunting)


•narcotic, hallucinatory (spiritual practices)


Others returned later to “functional” classification schemes


First written classification scheme from ancient Greeks

Theophrastos ca. 300 BC, studied under Plato and Aristotle, considered father of botany.

Described 500 plant species, including cotton, pepper, cinnamon, bananas and named many modern genera including Asparagus and Narcissus.

Classified all plants as trees, shrubs, subshrubs, herbs (different forms)


Functional (again)

Roman era

Pliny the Elder 23-79 AD

•wrote 37 volume Natural History encyclopedia

•9 volumes on medicinal plants

Dioscorides (first century AD)

•Roman military surgeon

•Wrote Materia medica

•Described 600 medicinal plants


Middle Ages

•Islamic Scholars preserved botanical works when Europe was in the Dark Ages




•Academic work began again in Europe

•Printing press invented in 1440 AD

•Herbals – books of flora (description of plants in a given area), focus on medicinal use (functional)

•Time of wide exploration

•Now instead of hundreds of plant species, 15,000 species to be classified

•In need of a new system to keep track


•Carl Linnaeus (1707-1778)

•Swedish botanist

•Attempted an artificial classification scheme

•A sexual system based on number  & arrangement of stamens

•Grouped unlike plants together (grouped cacti and cherries together)

•Linnaeus was much more successful in proposing a new system for naming plant species – Binomial nomenclature


Natural or Phentic Systems

Looks for “natural affinities” among species

No explicit methodology; largely intuitive

de Jussieu and de Candolle important early works (1700s, early 1800s)

Bentham and Hooker (mid-1800s)

•British botanists

•Accepted Darwin’s theory of evolutionary change (1859)

•But grouped plants just by similar features, not recognizing potential for change



Group plants by evolutionary relationships

Engler (1844-1930)

Compiled a very detailed flora of all known vascular plants, with extensive illustrations and keys, arranging plant families according to contemporary theory of phylogeny

We currently recognize a different sequence of phylogeny, but Engler’s work remains valid in its exhaustive detail.


Current classification schemes remain based on our understanding of phylogenetic relationships among plants.

Important 20thC botanists in this effort include:

•Charles Bessey

•John Hutchinson

•Arthur Cronquist

Each has built upon the works of earlier botanists.

Classification is still a work in progress.


The Taxonomic Hierarchy

•Each category is called a “taxon” (plural = taxa)

•Higher taxa are more inclusive

•Names of most taxa (except Kingdom and above genus) are of a genus name with a suffix indicating taxonomic level

            phylum (or division) -ophyta 

            class                               -opsida          

                            order                                    -ales                

                                      family                              -aceae

•Taxa may be formed in between these groups (subclass, tribe, etc.) but we won’t use them.



Species names

Linnaeus was much more successful in proposing a new system for naming plants

Old system used Latin phrase names

For example, spearmint was known as:

“Mentha floribus spicatis, foliis oblingis serratis”

(Means mint, flowers in spike, leaves oblong and serrate)

Linnaeus proposed a binomial nomenclature

Spearmint becomes Mentha spicata


Species names

Carolus Linnaeus 


Species Plantarum

Publ. 1753

7,300 species


Proposed naming system called

Binomial Nomenclature




Species names

All species names have two basic words: genus plus specific epithet.  Genus is a noun, specific epithet is an adjective (or possessive noun) that modifies it.

Species names

                                    Linnaea borealis L.


            a. genus name

            b. specific epithet

            c. authority may be added

                        = who described (named) the plant 

                        often abbreviated, e.g. Linnaeus = L. or Linn.


Species names

Linnaea borealis L.


authority  required:

•First usage in a scientific publication

•On formal herbarium labels

•In Taxonomic literature


Species names

Rules for scientific names

•Underlined or italicized

•Use Latin words or words that have been Latinized

•First letter of genus name is always capitalized.  Rest of letters all lowercase. 

•Pseudotsuga menziesii




1. Every vowel (or pair of vowels) pronounced             Tolmiea

2. No silent letters at end                                              Cardamine

3. First letter silent when: pt, mn, cn, gn                        Pteridium

4. ll is l not y                                                                 Potentilla



Species names

Why use scientific and not common names?


Some species have more than one common name:

•Oregon myrtle in OR

•California bay in CA

•Umbellularia californica

•Plantago major has over 100 common names in several languages

Some common names are used for more than one species

•Cedar is used for species in at least 4 different general and two families

•Cedrus, Thuja, Chamaecyparis, Juniperus