Chapter 18
Chapter 18
CLASSIFICATION AND SY
CLASSIFICATION AND SYSTEMAT
STEMATICS
ICS
We have grouped organisms for easier study byWe have grouped organisms for easier study by comparing similarities and differences.comparing similarities and differences.
SYSTEMATICS
SYSTEMATICS: the study of the diversity of organisms and their comparative and: the study of the diversity of organisms and their comparative and evolutionary relationships. It
evolutionary relationships. It includes comparative includes comparative anatomy, comparative biochemistryanatomy, comparative biochemistry,, comparative physiology, etc.
comparative physiology, etc.
CLASSIFICATION OR TAXONOMY
CLASSIFICATION OR TAXONOMY is the ordering of organisms into groups. It is the ordering of organisms into groups. It includes the principles and procedures used in classification.
includes the principles and procedures used in classification.
PHYLOGENY
PHYLOGENY: refers to the evolutionary history of a species or group of species in: refers to the evolutionary history of a species or group of species in terms of their derivations through evolutionary processes; which species share a
terms of their derivations through evolutionary processes; which species share a commoncommon ancestor, which species share a
ancestor, which species share a more distant ancestor, etc.more distant ancestor, etc.
Systematics
Systematics is the study of biological diversity and ev is the study of biological diversity and evolutionary history of organisms.olutionary history of organisms. ystematics includes...
ystematics includes...
•
• TaxonomyTaxonomy, the science of identifying and classifying organisms., the science of identifying and classifying organisms. •
• Phyo!eneticsPhyo!enetics, the study of the evolutionary , the study of the evolutionary history of organisms.history of organisms. •
• Nomencat"#e$Nomencat"#e$ the system used in naming organisms. the system used in naming organisms.
!atural selection has shown that all organisms are r
!atural selection has shown that all organisms are related to each other genetically. elated to each other genetically. "ll"ll are part of a large phylogeny.
are part of a large phylogeny.
cientifically valid system of naming
cientifically valid system of naming plants #nomenclature$ should reflect phplants #nomenclature$ should reflect phylogeny,ylogeny, that is, evolutionary relationship.
that is, evolutionary relationship. "t the end of the
"t the end of the %I% Century, sci%I% Century, scientists began to develop a entists began to develop a natural system ofnatural system of
classification in which closely related organisms are classified together, and began to classification in which closely related organisms are classified together, and began to assign plant names on the basis of
assign plant names on the basis of phylogenetic relationship.phylogenetic relationship.
LE%ELS
LE%ELS OF T
OF TAXONOMIC CATEGORIES
AXONOMIC CATEGORIES
&he present system of nomenclature was devised
&he present system of nomenclature was devised by Carolus 'innaeus #Carl von 'inne$,by Carolus 'innaeus #Carl von 'inne$, a wedish botanist who lived in
a wedish botanist who lived in the 18th. Century.the 18th. Century.
'innaeus published in 1()* a boo+ called pecies lantarum, -the +inds of plants-. 'innaeus published in 1()* a boo+ called pecies lantarum, -the +inds of plants-.
•
• inomial system of nomenclature: /enus 0 species epithet scientific name inomial system of nomenclature: /enus 0 species epithet scientific name of theof the
plant. plant.
•
•
• " ta3onomic grouping is called a" ta3onomic grouping is called ataxontaxon.. •
• &a&a3onomy is hierarchical: ta3a are grouped 3onomy is hierarchical: ta3a are grouped into broader ta3a.into broader ta3a.
S&ecies
S&ecies are grouped into are grouped into!ene#a!ene#a #sing. /enus$. #sing. /enus$.
•
• /enera into/enera into'amiies'amiies; families into; families into o#(e#so#(e#s; orders into; orders intocassescasses; classes into; classes into(i)isions(i)isions;;
divisions into
divisions into *in!(oms*in!(oms..
•
• &here are intermediate ta3onomic categories, e.g. &here are intermediate ta3onomic categories, e.g. superfamily or subspecies.superfamily or subspecies.
43cept for the +ingdom, genus and species level, the ta3on must have a certain ending to 43cept for the +ingdom, genus and species level, the ta3on must have a certain ending to indicate the classification level:
indicate the classification level:
55 phyta phyta for 6ivision, e.g. Chlorophyta for 6ivision, e.g. Chlorophyta 55 opsidaopsida for Class, e.g. 'iliopsida for Class, e.g. 'iliopsida 55 alesales for 7rder, e.g. abales for 7rder, e.g. abales 55 aceaeaceae for amily, e.g. abaceae for amily, e.g. abaceae
4ach family name is named after one of its genera, e.g. 9osaceae after the genus
4ach family name is named after one of its genera, e.g. 9osaceae after the genus Rosa Rosa.. ome old names used before the adoption of the new rules of nomenclature have been ome old names used before the adoption of the new rules of nomenclature have been conserved by convention. &hese are named
conserved by convention. &hese are named nomina conservandanomina conservanda, conserved names., conserved names.
•
• or e3ample: the daisies and asters family have two names, a conserved old name,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, Compositae, and a new name according to the modern rules of nomenclature, "steraceae. oth are eually valid.
"steraceae. oth are eually valid.
CLADISTICS
CLADISTICS
" species evolves into two species, as populations accumulate distinct alleles. " species evolves into two species, as populations accumulate distinct alleles. &he two new species usually strongly resemble one another.
&he two new species usually strongly resemble one another. 9eproductive isolation prevents the sharing of new
9eproductive isolation prevents the sharing of new alleles caused by mutations.alleles caused by mutations. lants may resemble one another because
lants may resemble one another because 1.
1. &he&hey evy evolvolved fed from rom a coa commmmon anon ancescestor tor <.
<. &he&hey have uy have undendergrgone coone convernvergengent evolt evolutiutionon " feature or a trait is called a
" feature or a trait is called a cha#acte#+cha#acte#+
•
• " character may be a morphological characteristic, e.g. presence of hairs, shape of " character may be a morphological characteristic, e.g. presence of hairs, shape of
shell, etc. shell, etc.
•
• " character may also be a trait at the cellular, biochemical or molecular level, e.g." character may also be a trait at the cellular, biochemical or molecular level, e.g.
a particular nucleotide seuence. a particular nucleotide seuence.
" character may have several
" character may have severalcha#acte# statescha#acte# states, e.g. white or purple flowers, hairs long or , e.g. white or purple flowers, hairs long or short, "
short, " base or C base or C base in particular nucleotide base in particular nucleotide seuence.seuence.
•
• Ancest#a o# &esiomo#&hic cha#acte#sAncest#a o# &esiomo#&hic cha#acte#s are found in the common ancestor of are found in the common ancestor of
daughter species. daughter species.
o
o Sym&esiomo#&hic cha#acte#sSym&esiomo#&hic cha#acte#s are ancestral characters shared by modern are ancestral characters shared by modern
clades. clades.
•
• De#i)e( o# a&omo#&hic cha#acte#sDe#i)e( o# a&omo#&hic cha#acte#s have evolved from the have evolved from the ancestral character.ancestral character.
o
o Syna&omo#&hicSyna&omo#&hic characters are derived characters found in two or more characters are derived characters found in two or more
species and suggest a close common ancestor. species and suggest a close common ancestor. hared derived characters are evidence
hared derived characters are evidence of evolutionary relationship.of evolutionary relationship. &he resemblance of plants that result when two
&he resemblance of plants that result when two distinct evolutionary lines respond todistinct evolutionary lines respond to similar environments and selection pressures is called
similar environments and selection pressures is called con)e#!ent e)o"tioncon)e#!ent e)o"tion.. &a3a may be similar because they share ancestral
&a3a may be similar because they share ancestralcha#acte# statescha#acte# states or derived character or derived character states, but only the derived character states that are shared among ta3a indicate
states, but only the derived character states that are shared among ta3a indicate monophyletic groups and enable
monophyletic groups and enable us to infer phylogeny successfully.us to infer phylogeny successfully.See the example onSee the example on page 416, cacti and succulent euphorbs.
page 416, cacti and succulent euphorbs.
Character states that are restricted to a single lineage are sometimes called Character states that are restricted to a single lineage are sometimes called
a"ta&omo#&hies a"ta&omo#&hies..
•
• Homoo!yHomoo!y: same feature in different species is derived from a common ancestor, e.g.: same feature in different species is derived from a common ancestor, e.g.
the forelimb of vertebrates. the forelimb of vertebrates.
•
• Homo&asyHomo&asy: a feature that has evolved : a feature that has evolved two or more time independently of the two or more time independently of the otherother
and thus does not have a common origin. 2omoplasies are also called
and thus does not have a common origin. 2omoplasies are also calledanao!o"sanao!o"s 'eat"#es
'eat"#es or characters. or characters.
Study the vocabulary on Table 18.3, page 41. Study the vocabulary on Table 18.3, page 41.
Study !"acti as #xamples o$ #volutionary %iversi$ication&, pages 4 ' 4(. Study !"acti as #xamples o$ #volutionary %iversi$ication&, pages 4 ' 4(. 6issimilariti
6issimilarities between es between plants can be plants can be difficult to assess.difficult to assess.
=utations that affect production, distribution, and sensitivity to hormones result in large =utations that affect production, distribution, and sensitivity to hormones result in large changes of the phenotype between two closely related species.
changes of the phenotype between two closely related species.
=utations that affect early stages of development such as the embryo or bud meristems =utations that affect early stages of development such as the embryo or bud meristems can cause closely related species to
Certain features are considered more significant in evaluating e
Certain features are considered more significant in evaluating e volutionary relationship.volutionary relationship.
•
• eatures that are the result of comple3 metabolic interactions and the influence ofeatures that are the result of comple3 metabolic interactions and the influence of
many genes tend to evolve
many genes tend to evolve more slowly than those with simple metabolic controlsmore slowly than those with simple metabolic controls by one or two genes.
by one or two genes.
6!" seuencing is a new tool for analy>ing evolutionary relationships. 6!" seuencing is a new tool for analy>ing evolutionary relationships.
6!" seuencing has its own limitations and ambiguities, e.g. how many nucleotide 6!" seuencing has its own limitations and ambiguities, e.g. how many nucleotide differences are needed to conclude
differences are needed to conclude that two genomes represent two distinct species?that two genomes represent two distinct species? @!649&"
@!649&"!6I!/ !6I!/ C'"67/9"=C'"67/9"= "
"ca(o!#amca(o!#am is a diagram that shows evolutionary patterns by means is a diagram that shows evolutionary patterns by means of a series ofof a series of branches.
branches.
4ach point at which a cladogram branches is called a node and represents the divergence 4ach point at which a cladogram branches is called a node and represents the divergence of one ta3on into two ta3a.
of one ta3on into two ta3a.
"ll branches that e3tend from any
"ll branches that e3tend from any particular point represent the descendants of theparticular point represent the descendants of the original group, their
original group, their common ancesto#common ancesto#..
&he ancestor and all the branches derived from it represent a
&he ancestor and all the branches derived from it represent a ca(eca(e.. " node represents a detectable change that created the
" node represents a detectable change that created the two new groups.two new groups. See )ig. 18.4.See )ig. 18.4. hared derived characters are evidence
hared derived characters are evidence of evolutionary relationship.of evolutionary relationship. hylogenetic classification should be
hylogenetic classification should be mono&hyeticmono&hyetic.. =onophyletic means that all the members of a
=onophyletic means that all the members of a ta3on regardless of ran+, are descendantsta3on regardless of ran+, are descendants of a common ancestor.
of a common ancestor.
When a clade does not include all the descendants of the most recent common ancestors, When a clade does not include all the descendants of the most recent common ancestors, it forms a
it forms a &a#a&hyetic !#o"&&a#a&hyetic !#o"&.. 7rganisms in a
7rganisms in a&oy&hyetic !#o"&&oy&hyetic !#o"& evolved from evolved from different ancestors.different ancestors.
•
• &he&he in!#o"&in!#o"& refers to the monophyletic group of species whose phylogeny we refers to the monophyletic group of species whose phylogeny we
want to want to infer.infer.
•
• &he&he o"t!#o"&o"t!#o"& is made of more distantly related ta3a. is made of more distantly related ta3a. •
• Siste# !#o"&sSiste# !#o"&s are groups species derived from a c are groups species derived from a common ancestor that is notommon ancestor that is not
shared with any other group. shared with any other group.
Pa#simony
Pa#simony refers to the principle that states that the simplest e3planation reuiring the refers to the principle that states that the simplest e3planation reuiring the least number of undocumented assumptions, should be
least number of undocumented assumptions, should be preferred over more complicatedpreferred over more complicated hypotheses that reuire more assumptions for which evidence is lac+ing.
hypotheses that reuire more assumptions for which evidence is lac+ing.
•
• &he best estimate of true phylogeny reuires the &he best estimate of true phylogeny reuires the fewest number of evolutionaryfewest number of evolutionary
changes. changes.
If the data indicates that the simplest e3planation is no
If the data indicates that the simplest e3planation is no t accurate, then the scientist movest accurate, then the scientist moves on to the ne3t
on to the ne3t simplest hypothesis.simplest hypothesis.
Computers and statistical analysis are used to construct cladograms. Computers and statistical analysis are used to construct cladograms.
7ften computers come up with several cladograms that are eually simple but have the 7ften computers come up with several cladograms that are eually simple but have the ta3a arranged d
ta3a arranged differentlyifferently. &his situation is called. &his situation is called,e-"ay &a#simonio"s+.,e-"ay &a#simonio"s+.
When several species or clades are shown to arise from the same node, an
When several species or clades are shown to arise from the same node, an "n#eso)e("n#eso)e( &oychotomy
&oychotomy results. results.
C'"67/9"= "!6 &"%7!7=IC C"&4/79I4 C'"67/9"= "!6 &"%7!7=IC C"&4/79I4 &he only ta3onomic category
&he only ta3onomic category with an obAective definition is the species. &here is no with an obAective definition is the species. &here is no suchsuch an obAective definition
an obAective definition for genus, family, etc.for genus, family, etc. =ost cladograms are not stable. &hey change
=ost cladograms are not stable. &hey change as new data becomes available.as new data becomes available. =any systematists continue to use the old names for
=any systematists continue to use the old names for genera, families and orders untilgenera, families and orders until they are shown to be paraphyletic or polyphyletic.
they are shown to be paraphyletic or polyphyletic.
&his results into several well5+nown families being divided into two or combined &his results into several well5+nown families being divided into two or combined intointo one.
one.
•
• or e3ample. &he old name Bdicots has been abandoned because it has beenor e3ample. &he old name Bdicots has been abandoned because it has been
shown to be paraphyletic. It included the Bbasal angiosperms and Beudicots but shown to be paraphyletic. It included the Bbasal angiosperms and Beudicots but left the monocots out, which share a
left the monocots out, which share a common ancestor with the Beudicots.common ancestor with the Beudicots. SeeSee )ig. 18.6.
)ig. 18.6.
•
• Basal angiosperms and Beudicots are informal names.Basal angiosperms and Beudicots are informal names.
OTHER TYPES OF CLASSIFICATION SYSTEMS OTHER TYPES OF CLASSIFICATION SYSTEMS A#ti'icia cassi'ication systems
A#ti'icia cassi'ication systems are based on easy to observe characters, e.g. guides to are based on easy to observe characters, e.g. guides to wild flowers based on
wild flowers based on flower color.flower color.
&heir goal is easy plant identification and
&heir goal is easy plant identification and not to show evolutionary relationship.not to show evolutionary relationship.
Cassi'ication systems 'o# 'ossis
&he goal is to understand to
&he goal is to understand to evolution of the fossil and to indentify both evolution of the fossil and to indentify both its ancestors andits ancestors and its relatives that might have later evolved into
its relatives that might have later evolved into other species.other species.
ecause data about fossils is usually very poor, fossils have been grouped
ecause data about fossils is usually very poor, fossils have been grouped based onbased on superficial similarities. &hese groupings are called
superficial similarities. &hese groupings are called ,'o#m !ene#a+.,'o#m !ene#a+.
"ll fossils with the same
"ll fossils with the same basic form or structure are basic form or structure are classified together.classified together.
NE/ SPECIES NE/ SPECIES
When a new species is found, it must be described and given a new name that has not When a new species is found, it must be described and given a new name that has not been used before.
been used before.
" specimen that fi3es the name of the species must be designated. &his is called the " specimen that fi3es the name of the species must be designated. &his is called thety&ety&e s&ecimen o# hooty&e+
s&ecimen o# hooty&e+
&he naming of a new species must be done according to the rules of nomenclature &he naming of a new species must be done according to the rules of nomenclature published in
published in *nternational "ode o$ +otanical omenclature *nternational "ode o$ +otanical omenclature.. 6uplicates of the type are called
6uplicates of the type are calledisoty&esisoty&es. Isotypes are usually distributed to other. Isotypes are usually distributed to other herbaria to facilitate the study of the species and to prevent the accidental destruction of herbaria to facilitate the study of the species and to prevent the accidental destruction of the holotype
the holotype
MA0OR LINES OF E%OL1TION MA0OR LINES OF E%OL1TION
'ife probably originated about *.) billion years ago 'ife probably originated about *.) billion years ago
&he first cells were very simple, consisting of a cell membrane,
&he first cells were very simple, consisting of a cell membrane, protoplasm, and someprotoplasm, and some means of inheritance, probably 9!". &hey lac+ nucleus and membrane bound organelles means of inheritance, probably 9!". &hey lac+ nucleus and membrane bound organelles in all
in all probabilityprobability..
7rganisms without membrane bound organelles are called
7rganisms without membrane bound organelles are called&#o*a#yotes&#o*a#yotes. ro+aryotes may. ro+aryotes may be e3tinct or living.
be e3tinct or living.
E"*a#yotes
E"*a#yotes possess membrane bound organelles. &hey evolved from pro+aryotes. possess membrane bound organelles. &hey evolved from pro+aryotes. &he
&he en(osym2iosis theo#yen(osym2iosis theo#y attempts to e3plain the origin of attempts to e3plain the origin of eu+aryotes.eu+aryotes. &here are three 6omains: acteria, "rchaea and 4u+arya.
