Ch18 Classification

Chapter 18

CLASSIFICATION AND SYSTEMAT SY STEMATICS ICS

We have grouped organisms for easier study by comparing similarities and differences. SYSTEMATICS : the study of the diversity of organisms and their comparative and evolutionary relationships. It includes comparative anatomy, comparative biochemistry, biochemistry, comparative physiology, etc. CLASSIFICATION OR TAXONOMY  is the ordering of organisms into groups. It includes the principles and procedures used in classification. PHYLOGENY : refers to the evolutionary history of a species or group of species in terms of their derivations through evolutionary processes; which species share a common ancestor, which species share a more distant ancestor, etc.

ev olutionary history of organisms. Systematics  is the study of biological diversity and evolutionary ystematics includes... •

Taxonomy, the science of identifying and classifying organisms.

•

Phyo!enetics , the study of the evolutionary history of organisms.

•

Nomencat"#e$  the system used in naming organisms.

 !atural selection has shown that all organisms are related related to each other genetically. "ll are part of a large phylogeny. cientifically valid system of naming plants #nomenclature$ should reflect phylogeny, ph ylogeny, that is, evolutionary relationship. "t the end of the %I% Century, scientists scientists began to develop a natural system of classification in which closely related organisms are classified together, and began to assign plant names on the basis of phylogenetic relationship.

LE%ELS OF TAXONOMIC TAXONOMIC CATEGORIES &he present system of nomenclature was devised by Carolus 'innaeus #Carl von 'inne$, a wedish botanist who lived in the 18th. Century. 'innaeus published in 1()* a boo+ called pecies lantarum, -the +inds of plants-. •

•

inomial system of nomenclature: /enus 0 species epithet  scientific name of the  plant. 2ierarchical classification: groups within groups.

• •

" ta3onomic grouping is called a taxon. &a3onomy &a3onomy is hierarchical: ta3a are grouped into broader ta3a.

S&ecies  are grouped into !ene#a #sing. /enus$. •

•

/enera into 'amiies ; families into o#(e#s; orders into casses ; classes into (i)isions ; divisions into *in!(oms . &here are intermediate ta3onomic categories, e.g. superfamily or subspecies.

43cept for the +ingdom, genus and species level, the ta3on must have a certain ending to indicate the classification level: 5 5 5 5

 phyta for  phyta for 6ivision, e.g. Chlorophyta opsida for opsida for Class, e.g. 'iliopsida ales for ales for 7rder, e.g. abales aceae for aceae for amily, e.g. abaceae

4ach family name is named after one of its genera, e.g. 9osaceae after the genus Rosa genus Rosa.. ome old names used before the adoption of the new rules of nomenclature have been conserved by convention. &hese are named nomina conservanda, conservanda, conserved names. •

or e3ample: the daisies and asters family have two names, a conserved old name, Compositae, and a new name according to the modern rules of nomenclature, "steraceae. oth are eually valid.

CLADISTICS " species evolves into two species, as populations accumulate distinct alleles. &he two new species usually strongly resemble one another. 9eproductive isolation prevents the sharing of new alleles caused by mutations. lants may resemble one another because 1. &hey &hey evolv evolved ed from from a comm common on ances ancestor  tor