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)

More on this later

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.