the science of plant systematics plant systematics (pbio 309/509) harvey ballard
TRANSCRIPT
The Science of Plant Systematics
Plant Systematics (PBIO 309/509)
Harvey Ballard
Traditional Meaning of “Plant” 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 Extant land plants =
liverworts hornworts mosses vascular plants
(tracheophytes) Course touches briefly on
ferns & allies and gymnosperms
Focuses on angiosperms
Judd et al. (2002)
What is Systematics? 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? 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? Uses diverse
approaches: Morphology Anatomy Palynology Microscopy Biochemistry
Molecular Biology
Genetics Physiology Ecology Evolution Bioinformatics
Why is Systematics Important? 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? 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 Systematics sensu stricto
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 Systematics sensu stricto
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 Taxonomy
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 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 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 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 Three types of relationship possible
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 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)
The Phylogenetic Approach in Practice
Monophyletic groups retained
Others recircumscribed Alternative “endpoints”
along continuum Lump all taxa in
broader group Subdivide more finely
Judd et al. (2002)
The Phylogenetic Approach in Practice Example #1:
Monocots monophyletic
Monocots nested within dicots
Dicots paraphyletic with respect to monocots
Judd et al. (2002)
The Phylogenetic Approach in Practice Solution to
Example #1: Retain Monocots Recognize “Basal
Monocot” lineages
Recognize “Eudicots”
Judd et al. (2002)
Basal D
icots Magnoliids
Monocots
Eudicots
The Phylogenetic Approach in Practice Solution to
Example #1: Higher-level
groupings also supported by: Embryology Major
biochemical compounds
Pollen types
Basal D
icots Magnoliids
Monocots
Eudicots
Judd et al. (2002)
The Phylogenetic Approach in Practice Example #2
Genus Hybanthus is 3rd largest in the Violaceae—up to 125 spp.
Similar in gross floral features, herb to shrub habit
H. monopetalus(Gordon, photo)
H. communisH. concolor(Barnes, 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
Hybanthus is highly polyphyletic
Merger across family would lump extensive phenotypic diversity
Investigation of Hybanthus initiated
Pombalia (55-60 spp., Latin America)Isodendrion
Hybanthus, s.str. (4 spp., Mesoamerica)Hybanthus fruticulosus complex
Hybanthus thiemei complex
AgateaCorynostylis
Anchietea
Melicytus, s.l.Hybanthus enneaspermus complex
Viola
Noisettia
Allexis
Amphirrhox longifolia
Leonia
Gloeospermum
OrthionMayanaeaCubelium (Hybanthus concolor,
Pigea (13 spp., S. Australia &
Paypayrola
Hekkingia
Rinorea crenataRinorea (other spp.)
Fusispermum
Passiflora (OUTGROUP)
(2 spp., Mexico)
(2 spp., Mesoamerica)
(ca. 15-30 spp., Africa to N. Australia)
New Caledonia)
E. North America)
The Phylogenetic Approach in Practice
Hybanthus groups differ dramatically in: Flower symmetry Stamen morphology Seed morphology Chromosome number Pollen morphology Xylem morphology
Similar only in expanded bottom petal
Pombalia (Latin America)IsodendrionHybanthus, s.str. (Mesoamerica)Hybanthus fruticulosus complex
Hybanthus thiemei complex
AgateaCorynostylis
Anchietea
Melicytus, s.l.Hybanthus enneaspermus complex
Viola
NoisettiaAllexis
Amphirrhox longifoliaLeonia
GloeospermumOrthionMayanaea
Cubelium (E.North America)Pigea (S. Australia &
PaypayrolaHekkingia
Rinorea crenataRinorea (other spp.)FusispermumPassiflora (OUTGROUP)
(Mexico)
(Mesoamerica)
(Africa to N. Australia)
New Caledonia)
16 [12]8
8
16, 328[4]6-120
[4]6, 12, 24
24
24, 48
X = 8
X = 24(6?)
The Phylogenetic Approach in PracticeTrait: Corolla zygomorphy (lateral:bottom petal length
ratio)Pombalia 0.33-0.71 [0.8-1.00]Hybanthus 0.90-1.00H. fruticulosus complex 0.89-0.95H. thiemei complex 0.50-0.55H. enneaspermus comp. 0.38-0.66Cubelium 0.75-0.80Pigea 0.30-0.66
The Phylogenetic Approach in Practice
Trait: Attachment of staminal glands on filament
H. fruticulosus H. enneaspermus Pigea complex complex
medialattachment
basalattachment
Red line isBase offilament
The Phylogenetic Approach in Practice
Trait: Seeds, in relative size proportion
Pombalia Hybanthus H. fruticulosuscomplex
H. thiemei H. enneaspermus Pigea Cubelium complex complex
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 0
Pigea
The Phylogenetic Approach in Practice “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 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.