Plant Taxonomy

1. Plant Taxonomy

2. Definitions • Taxonomy (systematics) - the study and description of the variation of organisms, the investigation of the causes and consequences of this variation, and the manipulation of the data obtained to produce a system of classification • Classification (as process) - the production of a logical system of categories, each containing any number of organisms, which allows easier reference to its components, the kinds of organisms • Classification (as object) - is that logical system itself

3. Definitions cont’d • Identification - naming of an organism by reference to an already existing classification system • Taxon - any taxonomic grouping - phylum, class, family, genus, etc. • Description - statement of the characteristics of a taxon • Characters that contribute to a taxonomic description are known as taxonomic or systematic characters

4. Definitions cont’d • flora (lower case) - plant life of a given area • Flora (upper case) is a book or other work describing the flora of a given area

5. Need for Classification • need for some system of classification is absolute, because it is only by first naming organisms and then grouping them in recognizable categories that we can begin to sort out and understand the vast array of diversity which exists • Our current estimate is that there are about 280,000 total plant species; with 263,000 species of higher vascular plants that have been described and named - ferns, gymnosperms, flowering plants - about 2,000 new species of flowering plant are described every year

6. Southern magnolia – Magnolia grandifolia

8. Hierarchies of plant taxonomy – from Stace

9. Taxonomic Systems • Predictivity - Ideally our systems of classification should allow us to place similar species of plants together in the same category

11. Two Types of Classification Schemes • Artificial classification schemes - these systems allow one to quickly categorize a particular organism, usually so that it can be quickly found in a book or a herbarium • Natural classification scheme - organize together related groups of plants and have a high degree of predictive power

12. Artificial Classification Scheme

13. Artificial Classification Scheme Red Trillium White Trillium

14. Natural Classification Scheme – For Seed Plants

15. Ancient Classifications

16. Oaks - Fagaceae

17. Maples - Aceraceae

18. Pennisetum – a grass - Poaceae

19. Carex – sedge meadow - Cyperaceae

20. Juncus – rushes - Juncacaea

21. Vegetables from Brassica oleracea Brassicaceae

22. Theophrastus 370-285 BCE

23. Dioscorides – 1st Century AD

24. Page from 15th century Arabic edition of Dioscorides herbal

25. Leonhart Fuchs - 1542

26. Fuchs’s History of Plants - 1542

27. Gerard’s Herbal 1597

28. Gaspar Bauhin - 1623

29. 1623 – first use of binomial names

30. Carolus Linneaus

31. Systema Naturae – first published 1735

32. Classification After Darwin

33. Evolutionary Classification Schemes • Botanists have tried to develop classification systems that are natural and also show evolutionary relationships - this has been surprisingly hard to do • In developing classification systems, we attempt to group plants which share advanced or derived characteristics - presumably these characters have only arisen once or at most a few times - it is not always easy to tell what is an advanced character though

34. Natural Classification Scheme – For Seed Plants

35. Basics of Characters • A taxonomic character is any expressed attribute of an organism that can be evaluated and that has two or more discontinuous states or conditions - for example the number of petals on a flower - can be in 3's, 4's or 5's - thus distinct states and they are discontinuous • The taxonomic value of a characteristic is increased if the biological significance of the characteristic has been determined

36. Goat Dandelion - Asteraceae

37. Buttercup - Ranunculaceae

38. Morphology • Plants are highly plastic in their growth forms - how tall they grow, their shape will vary depending upon environment and growing conditions • However reproductive structures tend not to differ in form from plant to plant of the same species - they may differ in number, but form is conservative - flowers, cones tend to be similar within all members of a species - thus much plant classification and identification is based upon reproductive structures

40. Umbel – flower head in Apiaceae

41. Brassicaceae – The mustards

42. Oak acorns - Fagaceae

43. Birch catkin Betulaceae

44. Other important characteristics • Internal anatomy – mostly important for studies of evolutionary relationships – not often used in identification guides  • Physiology – mostly for classifying parasites and saprobes (plants that decompose dead matter)  • Chemistry – can be important because some groups have distinct chemical compounds – the mints are aromatic with distinct odor • DNA –there is interest in developing easy methods to differentiate species based on short sequences of DNA – much work done with the DNA for RuBisCO – an important enzyme in photosynthesis • Ecology and geography can also be important – some plant species or families are restricted to particular environments or geographic areas

45. Mint

47. Cactus