The Science of Plant Systematics

1. The Science of Plant Systematics Plant Systematics (PBIO 309/509) Harvey Ballard

2. 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

3. 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)

4. 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)

5. 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?

6. Uses diverse approaches: Morphology Anatomy Palynology Microscopy Biochemistry Molecular Biology Genetics Physiology Ecology Evolution Bioinformatics What is Systematics?

7. 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

8. 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

9. 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

10. 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)

11. 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

12. 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

13. 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

14. 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)

15. 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

16. The Phylogenetic Approach A: monophyletic B: paraphyletic A+B: polyphyletic Judd et al. (2002)

17. 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

18. 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)

19. The Phylogenetic Approach in Practice • Example #1: • Monocots monophyletic • Monocots nested within dicots • Dicots paraphyletic with respect to monocots Judd et al. (2002)

20. 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)

21. 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)

22. 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)

23. 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

24. Pombalia (55-60 spp., Latin America) Isodendrion 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 • Hybanthus is highly polyphyletic • Merger across family would lump extensive phenotypic diversity • Investigation of Hybanthus initiated

25. 16 [12] Pombalia (Latin America) 8 Isodendrion Hybanthus, s.str. (Mesoamerica) Hybanthus fruticulosus complex (Mexico) Hybanthus thiemei complex (Mesoamerica) X = 8 8 Agatea Corynostylis Anchietea 16, 32 Melicytus, s.l. Hybanthus enneaspermus complex 8 (Africa to N. Australia) [4]6-120 Viola Noisettia Allexis Amphirrhox longifolia Leonia Gloeospermum X = 24 (6?) Orthion Mayanaea 24 Cubelium (E.North America) Pigea (S. Australia & [4]6, 12, 24 New Caledonia) Paypayrola Hekkingia Rinorea crenata 24, 48 Rinorea (other spp.) Fusispermum Passiflora (OUTGROUP) 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

26. 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 complex0.89-0.95 H. thiemei complex 0.50-0.55 H. enneaspermus comp. 0.38-0.66 Cubelium 0.75-0.80 Pigea 0.30-0.66

27. The Phylogenetic Approach in Practice Trait: Attachment of staminal glands on filament medial attachment basal attachment Red line is Base of filament H. fruticulosusH. enneaspermusPigea complex complex

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

29. The Phylogenetic Approach in Practice Summary of 12 Traits at a Glance

30. 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

31. 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.