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Diversity of & Phylogeny of Plants
Classification: Assigning to categories.
Goal of classification: designate logical and
“natural” groups.
Carl Linnaeus (Sweden, 1707-1778) an
early pioneer in plant classification. First
to use Binomial (2 word) system of
naming species.
Carl Linnaeus
Classification & Phylogeny
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Since Darwin’s time, prevailing idea: Classification should
reflect evolutionary relationships.
Phylogeny = Evolutionary lineage
Classification should reflect phylogeny:
Phylogenetic relationships can be expressed by Phylogenetic
trees.
Ideally, all named groups should be one complete branch of a
phylogenetic tree.
A Phylogenetic tree
Modern Methods to Uncover
Phylogeny
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Cladistics: Modern method for comparing organisms to determine
relationships.
Relationships based on “shared derived characters”.
Shared ancestral characters don’t give evolutionary info:
• It’s expected that they could occur in any group in the lineage.
Goal: recover branching pattern of evolution.
Product: cladogram -branching tree (p. 1378)
Clubmosses
Ferns Pines Oaks
Cladogram
Classification Groups & Phylogeny
p. (1373):
Monophyletic group: One complete evolutionary lineageancestor & all descendants.
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Ideally all named groups should be monophyletic.
Polyphyletic group: Several lineages- members don’t share a
single ancestor.
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All taxonomists seek to identify & eliminate these.
Paraphyletic group: One ancestor but not all descendants.
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Examples: Reptiles, dicotyledons. (See pp. 1373-1378).
Cladists: These groups should not be recognized.
Monophyletic
Paraphyletic
Polyphyletic
Modern Trends in Plant Classification:
p. 1169-1192; (FNCT: 1373-1378, in part).
Increased emphasis on phylogeny.
New sources of taxonomic information
(DNA, etc.)
Emphasis on quantitative methods.
Debate between Cladistic & traditional
(Phenetic) schools.
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Phenetics: Use all available characters to
compare taxa. “Total distance” of prime
inportance.
Cladistics Use only known shared derived
characters; Only they have evolutionary
meaning.
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Branching pattern of evolution of
prime importance.
Recently: use of cladisitcs more common.
Recent Approaches to Classification
(p. 1163):
Angiosperm Phylogeny Group (APG)
Bremer, Chase, & Stevens (1988)
Attempts to reclassify flowering plants into monophyletic
groups (Family & Order-level) based on new Cladistic &
molecular research.
Basal
families
Magnoliids
Monocotyledons
Eudicotyledons
Classification of Organisms:
3 Domains
Archaea: (Non-bacterial
prokaryotes)
Bacteria: (true
bacteria)
Eukarya:
4 Traditional Kingdoms of Eukarya
“Protista”: (Eukaryotic cells, often single-celled
organisms.
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Euglenoids, Red Algae, Dinoflagelates, Diatoms,
Brown algae, Green algae…
“Catch-all” group: not monophyletic.
Includes green algae (=base of plant tree)!
Fungi: (Heterotrophic, external digestion).
Plantae: (multicellular autotrophs)
='embyophytes = 'higher
plants'.
Animalia: (Heterotrophs, internal digestion).
Bacteria
Archaea
“Protista”
Phylogeny of
Living things
Plants
Fungi
Animals
Phylogeny of Green Plants
Lycophytes
Mosses &
Ferns
Hornworts
Seed plants
Charophytes
Liverworts
Other
Green algae
Chlorophytes
Pteridophytes
Bryophytes
Gymnosperms
& Angiosperms
Green Algae
“Protista”
Green Algae
Share numerous cell characters with higher plants
Green algae + higher plants form a monophyletic clade.
Variable habit: Unicellular, colonial, multicellular.
Primarily fresh water.
Two main lineages:
Chlorophyte clade*.
Charophyte, other green algae, & higher plant clade.
Other
Green algae
Chlorophytes
Higher Plants
*Clade = monophyletic group e.g. 'CLADistics'
Green Algae
Chara: Member of a sister group to land plants
Chara at Lake Tombigbee, Alabama-Coushatta Indian
Reservation near Lvingston, TX
Bryophytes: Mosses, Liverworts & Hornworts:
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First land plants: Ordovician (510-439) M.Y.A. had some
bryophyte-like characteristics.
Said to be “transitional from green algae to vascular plants”.
3 distinct lineages (see title)
But: diverse, successful modern plants; NOT 'throwbacks'!
 occur worldwide in most habitats.
 2nd (mosses:15,000 sp.) & 4th (liverworts: 9,000 sp.)
largest plant groups!
Evolutionary strategies: different than vascular plants.
 Stay small & remain close to water source.
 Survive (rather than avoid) dehydration.
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Hornworts: Anthocerophyta
Sporophyte
Gametophyte
An East Texas Hornwort!
Sporophytes
Gametophyte
Liverworts: Hepatophyta (P. 352, 408)
A leafy liverwort
Gemma cups for
asexual propagation
A thallose liverwort
Liverworts: Hepatophyta (P. 352)
Sporophytes
Gametophyte
Mosses: Bryophyta
Capsule
(Sporangium)
Sporophyte
Gametophyte
Rhizoids
Mosses & other Bryophytes on Ravine Wall:
Sabine National Forest, East Texas
Vascular Plants
3 major clades:
Ferns
Lycophytes
Seed plants
The End!
Version 16.10