SYSTEMS OF CLASSIFICATION

Lecture Schedule

Lecture

Three ways of classifying plants

Artificial classifications
Natural classifications
Phylogenetic classifications

Folk Systematics: indigenous or ethnobiological classifications - how do humans classify?

5 (or 6) ethnobiological categories in all folk taxonomies

arranged hierarchically
unique beginner or kingdom (eg. plant, animal)
life form (tree, vine, grass)
generic taxa
specific and varietal usually rare

indigenous classifications - how do they compare to “scientific” systems?

correspondence of folk and systematic classifications?
monotypic vs. polytypic genera in folk vs. systematic classifications

History of classification: taxonomists and how they approached classification of plants

Ancients (2000 B.C. - A.D. 1500)

Theophrastes and “essentialism”
Classification by habitat
Emphasis on genus
“ladder of life” or “great chain of being” or “Scalae Naturae”

Herbalists (A.D. 1500 - 1580)

Pedanius Dioscorides (c. 40-90 A.D.) -— De Materia Medica and connection of Greek medicine, plants and classification
German herbalists and their “herbals” — classification by medicinal properties

The pivotal period — beginnings of natural thought (A.D. 1580 - 1800)

Andrea Caesalpino
John Ray — the concept of “class” [=orders]
Pierre Magnol — the concept of “family”
Carolus Linnaeus (Carl Linnaea) — Sexual System of classification in Species Plantarum: the ultimate mechanical (artificial) system

Period of natural systems (A.D. 1760 - 1880)

Antoine de Jussieau

Period of phylogenetic systems (A.D. 1859 - present)

Charles Darwin — impact of On the Origin of Species (1859) for classification

George Bentham & Joseph Hooker (KEW Royal Botanic Garden)

Adolph Engler & Karl Prantl

Die Naturlichen Pflanzenfamilien
“Salix = primitive”

Charles Bessey& his dicta or rules and “cactus” classification scheme

“Magnolia = primitive”

Contemporary taxonomists - see comparison of these and other classification systems

Arthur Cronquist, Armen Takhtajan, Robert Thorne, Rolf Dahlgren

Phylogenetics and molecular systematics (1993 – present)

its ongoing role in redefining classification

1993 — the first major classification based on DNA (rbcL of cpDNA) - see the 1993 rbcL sequencing study called Treezilla that redefined angiosperm systematics

the 1998 & 2003 APG classification systems — the Angiosperm Phylogeny Group

see APG system vs. Cronquist's system for dicots

 

Issues in phylogenetic classifications — grouping in hierarchial (“Linnaean”) systems

1. Problem of character convergences in defining higher taxonomic groupings and subjective choice of characters

2. Name of species remains the same; but name conveys knowledge of natural affinities and evolutionary relationships

3. Named groups are monophyletic (ancestors and all descendants); or at least paraphyletic but certainly not polyphyletic

4. Not all groups are named

5. Ranks are arbitrary and not of same age

 

“rankless” classification systems — the PhyloCode system (July 2004: 1st convention)

Replace “Linnaean” hierarchical system with “phylogenetic” classification system (and nomenclature)

1. groups given unranked names

2. groups defined by ancestry — i.e. phylogenetic tree

3. groups described/diagnosed by a character(s) on the branch of the monophyletic group

4. No types but specifiers for nodes on trees