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Angiosperm Classification From Linnaeus to the Angiosperm Phylogeny Group and beyond

Angiosperm Classification From Linnaeus to the Angiosperm Phylogeny Group and beyond. Historical concepts of relationships Linnaeus’ artificial classifications Natural classifications Molecular and Phylogenetic Revolution. Premolecular classification Artificial Natural Phylogenetic.

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Angiosperm Classification From Linnaeus to the Angiosperm Phylogeny Group and beyond

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  1. Angiosperm ClassificationFrom Linnaeus to the Angiosperm Phylogeny Group and beyond

  2. Historical concepts of relationships • Linnaeus’ artificial classifications • Natural classifications • Molecular and Phylogenetic Revolution

  3. Premolecular classification Artificial Natural Phylogenetic Molecular classifications Phylogenetic The building up of a natural classification: APG versus earlier classifications • Postmolecular classifications • Phylogenetic based on a wide array of characters including the molecular and micromorphological level

  4. Artificial classifications Perception of plant form has to be seen in a philosophical context as the encounter of man with plants Either as a man-centered approach… or as a perception of the real nature of things…

  5. The Scala naturae - concept attributed to Aristotle ranked things from the inorganic to humans and angels Early natural history work was motivated by the need to contemplate and understand ‘Gods work’

  6. Carolus Linnaeus (Carl von Linne) 1706-1778 • Linnaeus took it upon himself to classify the entire natural world His merit is that he showed that the basic unit of natural classification is not the individual but the species- a species is hold together by sex Artificial sexual system (based entirely on reproductive structures) Systema Naturae - the Linnean hierarchy

  7. Linnean hierarchy Phylum Spermatophyta (seed plants) Division Magnoliophyta (flowering plants) Class Magnoliopsida (Dicotyledons) Order Rosales Family Rosaceae Genus Prunus Species Prunus avium L. Each entity within the hierarchy is called a taxon (plur. taxa)

  8. The natural classifications These classifications were termed natural because they rejected Linnaeus artificial system, but used combinations of a limited number of characters Concept of “natural classification” in pre-Darwinian very different from ours - non evolutionary • J. B. Lamarck (1744-1829) Species could change through time by passing on traits acquired by individuals - a scala naturae in motion • A.-L. de Jussieu Genera plantarum - description of genera, families and classes • G. Bentham and J. Hooker (1862-1883) - Species plantarum

  9. Phylogenetic classifications

  10. Understanding relationships as an event of continuous evolution linked with ancestral forms - intuitive systems • German school - A.W. Eichler (1875); A. Engler and K. Prantl (1892) - Die natürlichen Pflanzenfamilien Woody apetalous plants are primitive (Amentiferae) - advanced = increase in complexity • Anglo-Saxon school - C. Bessey (1915) Woody Magnolia-like plants are primitive (Ranales) - advanced = increase in simplicity Abundant use of phylogenetic trees: Bessey 1915, Cronquist 1981, Takhtajan 1997, Thorne 1992 Dahlgrenogram: Dahlgren 1975

  11. The cactus-tree of C. Bessey (1915) • Dogmas of evolution • Woody herbaceous • Simple compound leaves • Perfect unisexual flowers • Many few floral parts • Hypo- epigyny Ranales most primitive Asteridae most derived His ideas are greatly influential for twentieth century evolutionary thought

  12. Relationships of Dicotyledons suggested by Cronquist (1968) - Subclasses are connected to each other by level of primitiveness and derivation Good didactic system and well documented: Families and genera of Flowering plants (1981)

  13. Dahlgren used a wide variety of chemical characters that he mapped on ‘Dahlgrenograms’ (a horizontal section of a tree in time.

  14. Classification of Thorne (1992) Even if the number of characters used in the systems increased considerably over the years, the lack of a well-defined methodology for analysing data made the system more intuitive than synthetical. The introduction of the cladistic methodology helped to solve this dilemma.

  15. Angiosperm Phylogeny Group • APG I (1998), APG II (2003),… • Textbook: Judd et al. (2002) Plant systematics. A phylogenetic approach • Contrary to intuitive premolecular systems “owned” by individuals and based on few characters, molecular phylogenetics are based on a high number of characters that have been analysed in statistical programs leading to hypotheses of relationships • Phylogenetic trees are produced by cladistic methods expressing relationships of sister groups in a phylogenetic context • The great challenge is to understand and interpret morphological characters in the framework of relationships presented by the molecular phylogenies

  16. A summary of the major groups that occurred in greater than 50% of the 1000 jackknife replicates (from Soltis et al. 2000).

  17. Asterids Rosids Core Eudicots Tricolpate pollen Saxifragales Caryophyllids Dilleniales Basal Eudicot grade Monocots Monosulcate pollen Magnoliids Basal Angiosperms ANITA grade Amborellaceae Simplified phylogenetic tree of APG II

  18. Flowering Plant Gateway Gatekeeper: Hugh D. Wilson The selection options on this page, and the menu bar below, provide various paths for exploration or comparison of four systems of flowering plant classification.  Selection of a Family name will query an index of web links relating to that Family or included taxa.  This 'gateway' system - eventually to include all vascular plants - is under constant revision.  Current options (menu bar at the base of this page) include: Cronquist A 'top down' view of the Cronquist System, starting with the Class/Subclass array and links to Cronquist Subclass pages.  This system is used by our course text and the lab herbarium. Takhtajan An entry to the Takhtajan System, starting with the Class/Subclass array that links to Takhtajan Subclass pages. Thorne A similar starting view of the Thorne System, with the Subclass, Superorder selection and resolution to Subfamily on Superorder pages. APG Informal elements of the Angiosperm Phylogeny Group system, with family listings in ordinal sequence where possible and full linkage to family placements of the other systems. Select Family An alphabetical selection menu that leads to listings of family names with links to either Cronquist or Thorne classification systems or, for non-flowering vascular plants, direct access to internet data for the family via queries to a full text index of URLs. Home Open this page. Handy if pursuit of family-level links (generated by selection of linked Family names) should lead far afield. http://www.csdl.tamu.edu/FLORA/newgate/cronang.htm

  19. Conclusions • Although the molecular phylogeny is a great improvement compared to earlier systems it is not the definite answer as it is a continuously evolving system. • Molecular systematics has its limitations with recurring convergent evolution. The cladistic methodology is also based on a priori assumptions that are not always accurate • In the future there is a need to combine of molecular data with new morphological data for understanding the evolution of angiosperm biodiversity.

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