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: Molecular Biology 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 Basal Dicots Solution to Example #1: Retain Monocots Recognize “Basal Monocot” lineages Recognize “Eudicots” Magnoliids Monocots Eudicots Judd et al. (2002)

The Phylogenetic Approach in Practice Basal Dicots Solution to Example #1: Higher-level groupings also supported by: Embryology Major biochemical compounds Pollen types 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. 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 Hybanthus, s.str. (4 spp., Mesoamerica) Hybanthus fruticulosus complex Hybanthus thiemei complex Agatea Corynostylis Anchietea Melicytus, s.l. Hybanthus enneaspermus complex Viola Noisettia Allexis Amphirrhox longifolia Leonia Gloeospermum Orthion Mayanaea Cubelium (Hybanthus concolor, Pigea (13 spp., S. Australia & Paypayrola Hekkingia Rinorea crenata Rinorea (other spp.) Fusispermum Passiflora (OUTGROUP) (2 spp., Mexico) (2 spp., Mesoamerica) (ca. 15-30 spp., Africa to N. Australia) New Caledonia) E. North America) Hybanthus is highly polyphyletic Merger across family would lump extensive phenotypic diversity Investigation of Hybanthus initiated

The Phylogenetic Approach in Practice Pombalia (Latin America) Isodendrion Hybanthus, s.str. (Mesoamerica) Hybanthus fruticulosus complex Hybanthus thiemei complex Agatea Corynostylis Anchietea Melicytus, s.l. Hybanthus enneaspermus complex Viola Noisettia Allexis Amphirrhox longifolia Leonia Gloeospermum Orthion Mayanaea Cubelium (E.North America) Pigea (S. Australia & Paypayrola Hekkingia Rinorea crenata Rinorea (other spp.) Fusispermum Passiflora (OUTGROUP) (Mexico) (Mesoamerica) (Africa to N. Australia) New Caledonia) 16 [12] 8 16, 32 [4]6-120 [4]6, 12, 24 24 24, 48 X = 8 X = 24 (6?) Hybanthus groups differ dramatically in: Flower symmetry Stamen morphology Seed morphology Chromosome number Pollen morphology Xylem morphology Similar only in expanded bottom petal

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 H. enneaspermus Pigea complex complex

The Phylogenetic Approach in Practice Trait: Seeds, in relative size proportion Pombalia Hybanthus H. fruticulosus complex H. thiemei H. enneaspermus Pigea Cubelium complex complex

The Phylogenetic Approach in Practice Summary of 12 Traits at a Glance Pombalia Hybanthus H. fruticulosus comp. H. thiemei comp. H. enneasp. comp. Cubelium 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.