Transcript What is Systematics, and Why is it Important?

The Science of Plant Systematics
Plant Systematics (PBIO 309/509)
Harvey Ballard
Traditional Meaning of “Plant”
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Autotrophs by
photosynthesis
Chlorophyll A, B
Storage of carbohydrates
(mostly starch)
Includes green algae
(Chlorophyta) and land
plants
Previously included fungi
and related groups, these
now removed as lineages
nearer to animals
Plant Groups Covered in This
Course
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Extant land plants =
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liverworts
hornworts
mosses
vascular plants
(tracheophytes)
Course touches briefly on
ferns & allies and
gymnosperms
Focuses on
angiosperms
Judd et al. (2002)
What is Systematics?
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Aims to recognize, describe, name, distinguish,
relate and classify earth’s organisms
Borrows from other fields--very much a
multidisciplinary, or “hybrid”, discipline
Supplies evidence to evolutionary biology,
ecology and other fields
Fundamental to all other scientific endeavors (and
many non-scientific human concerns)
Why is “Systematics” Fundamental?
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Why do we give names to entities?
Who cares if different labs studying mutations in
“Arabidopsis thaliana”, or investigating genetic
disease in “chimpanzees”, work with the same
organism across labs? How do we know?
How do we access information in libraries and
museums, in computer or cabinet files, or on the
internet?
What is Systematics?
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Uses diverse
approaches:
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Morphology
Anatomy
Palynology
Microscopy
Biochemistry
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Molecular
Biology
Genetics
Physiology
Ecology
Evolution
Bioinformatics
Why is Systematics Important?
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Detailed information at all hierarchical
levels is key to most scientific fields,
medicine and numerous aspects of human
society
Names of taxa (e.g., species), or even
individuals, are “tags” for information
retrieval and knowledge synthesis
Why is Systematics Important?
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Modern systematic studies provide
biological context to evolutionary and
ecological studies
Modern classifications are predictive, can
guide bioprospecting for medicines, foods,
etc.
Species-level information can guide
conservation
The Practice of Systematics
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Systematics sensu stricto
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Determination of distinct taxa using diverse
evidence
Inference of relationships using phenotypic or
genetic data
Classification of taxa into larger groups
Production of systematic revisions,
phylogenies, classification systems
The Practice of Systematics
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Systematics sensu stricto
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Name increasingly restricted to molecular
systematics (more sexy, generally more
fundable than unadulterated traditional
studies), commonly focused at or above
family level
Species-level systematics uncommon
Extras—evolutionary or biogeographic
hypotheses can be addressed empirically
Common at larger universities, largest
museums (few doing it)
The Practice of Systematics
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Taxonomy
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Nomenclature—application of names
(follows international rules)
Characterization and distinction of taxa from
field and herbarium studies
Production of monographs, floristic
treatments, checklists
Common in herbaria and museums, small
universities
The Practice of Systematics
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Above two subdisciplines fall along a continuum
Many botanists fall into one or other “category”
Determined partly by resources of individuals and
institutions—training, institutional aims, time,
money
Collaboration spans chasms between molecular
systematists who are not “experts” in a group and
“experts” lacking resources to do molecular
systematics
Phylogenetic Approach in This
Course
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Course uses current APG (Angiosperm
Phylogeny Group) classification as framework to
survey angiosperm families
Based heavily on Judd, et al.’s “Plant
systematics—A phylogenetic approach”, 2nd ed.
(2002), supplemented by Angiosperm Phylogeny
Website, etc.
Facilitates understanding of evolutionary change
“going up the tree”
Covers families in southeastern Ohio
The Phylogenetic Approach
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Phylogeny--branching
“tree” revealing
relationships of taxa
(species, genera, etc.)
Known taxa at branch
tips, connected by
hypothetical ancestors
Generated from diversity
of data, commonly DNA
sequences
More on algorithms later
Judd et al. (2002)
The Phylogenetic Approach
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Three types of relationship possible
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Monophyletic—common ancestor + all descendants
(“natural”)
Paraphyletic—common ancestor + some descendants
(“artificial”, generally rejected)
Polyphyletic--some descendants – ancestor
(“artificial”, rejected)
Monophyletic groups the only “natural” taxa
Para- and polyphyletic groups demand shifting
taxa around, or merging groups to achieve
acceptable classification
The Phylogenetic Approach
A: monophyletic
B: paraphyletic
A+B: polyphyletic
Judd et al. (2002)
The Phylogenetic Approach
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Genetic (DNA-based) data ideally used for
phylogeny reconstruction where available
Molecular data (in form of As, Cs, Gs and Ts)
provide numerous characters for evaluation of
relationships
Molecular phylogeny provides non-circular basis
for reexamining other evidence (e.g., phenotypic
traits)
More on this later
The Phylogenetic Approach in
Practice
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Monophyletic groups
retained
Others recircumscribed
Alternative “endpoints”
along continuum
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Lump all taxa in
broader group
Subdivide more finely
Judd et al. (2002)
The Phylogenetic Approach in
Practice
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Example #1:
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Monocots
monophyletic
Monocots nested
within dicots
Dicots
paraphyletic with
respect to
monocots
Judd et al. (2002)
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Solution to
Example #1:
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Retain Monocots
Recognize “Basal
Monocot”
lineages
Recognize
“Eudicots”
Judd et al. (2002)
Magnoliids
Monocots
Basal Dicots
The Phylogenetic Approach in
Practice
Eudicots
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Solution to
Example #1:
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Higher-level
groupings also
supported by:
Embryology
 Major
biochemical
compounds
 Pollen types
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Judd et al. (2002)
Magnoliids
Monocots
Basal Dicots
The Phylogenetic Approach in
Practice
Eudicots
The Phylogenetic Approach in
Practice
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Example #2
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Genus Hybanthus is 3rd largest in the Violaceae—up
to 125 spp.
Similar in gross floral features, herb to shrub habit
H. concolor
(Barnes, photo)
H. communis
H. monopetalus
(Gordon, photo)
The Phylogenetic Approach in
Practice
•92-112 species worldwide
•Diversity hotspots in N. Mexico, West Indies,
S.E. Brazil/Paraguay, E. Africa and S. Australia
The Phylogenetic Approach in
Practice
Pombalia (55-60 spp., Latin America)
Isodendrion
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Hybanthus is highly
polyphyletic
Merger across
family would lump
extensive
phenotypic
diversity
Investigation of
Hybanthus initiated
Hybanthus, s.str. (4 spp., Mesoamerica)
Hybanthus fruticulosus complex
(2 spp., Mexico)
Hybanthus thiemei complex
(2 spp., Mesoamerica)
Agatea
Corynostylis
Anchietea
Melicytus, s.l.
Hybanthus enneaspermus complex
(ca. 15-30 spp., Africa to N. Australia)
Viola
Noisettia
Allexis
Amphirrhox longifolia
Leonia
Gloeospermum
Orthion
Mayanaea
Cubelium (Hybanthus concolor,
E. North America)
Pigea (13 spp., S. Australia &
New Caledonia)
Paypayrola
Hekkingia
Rinorea crenata
Rinorea (other spp.)
Fusispermum
Passiflora (OUTGROUP)
The Phylogenetic Approach in
Practice
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Hybanthus groups differ
dramatically in:
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Flower symmetry
Stamen morphology
Seed morphology
Chromosome number
Pollen morphology
Xylem morphology
Similar only in
expanded bottom
petal
Pombalia (Latin America)
Isodendrion
16
8
[12]
Hybanthus, s.str. (Mesoamerica)
Hybanthus fruticulosus complex
(Mexico)
Hybanthus thiemei complex
(Mesoamerica)
Agatea
Corynostylis
Anchietea
Melicytus, s.l.
8
Viola
Noisettia
Allexis
Amphirrhox longifolia
Leonia
Gloeospermum
Orthion
Mayanaea
[4]6120
Cubelium (E.North America)
Pigea (S. Australia &
New Caledonia)
24
[4]6, 12,
24
X=8
16, 32
Hybanthus enneaspermus complex
8
(Africa to N. Australia)
Paypayrola
Hekkingia
Rinorea crenata
Rinorea (other spp.)
Fusispermum
Passiflora (OUTGROUP)
24, 48
X = 24
(6?)
The Phylogenetic Approach in
Practice
Trait: Corolla zygomorphy (lateral:bottom petal length
ratio)
Pombalia
0.33-0.71 [0.8-1.00]
Hybanthus
0.90-1.00
H. fruticulosus complex
0.89-0.95
H. thiemei complex
0.50-0.55
H. enneaspermus comp.
0.38-0.66
Cubelium
0.75-0.80
Pigea
0.30-0.66
The Phylogenetic Approach in
Practice
Trait: Attachment of staminal glands on filament
medial
attachment
basal
attachment
Red line is
Base of
filament
H. fruticulosus
complex
H. enneaspermus
complex
Pigea
The Phylogenetic Approach in
Practice
Trait: Seeds, in relative size proportion
Pombalia
H. thiemei
complex
H. enneaspermus
complex
Hybanthus
Pigea
H. fruticulosus
complex
Cubelium
The Phylogenetic Approach in
Practice
Summary of 12 Traits at a Glance
Pombalia
Hybanthus
0
H. fruticulosus comp.
H. thiemei comp.
H. enneasp. comp.
Cubelium
Pigea
0
The Phylogenetic Approach in
Practice
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“Cryptic” genera lumped earlier based on
gross flower similarities
Clades are distinct biogeographic units
“Hybanthus” = 4 New World genera, 3 Old
World ones
Each molecular clade = distinct genus
4 have earlier names, 3 require new ones
References
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Judd, W. S., C. S. Campbell, E. A. Kellogg,
P. F. Stevens, and M. J.
Donoghue. 2002. Plant systematics—A
phylogenetic approach, 2nd ed. Sinauer
Associates, Sunderland, MA. pp. 1-11.