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BIOB 518 Presentation_Part_I.pdf

  1. 1. SURVEY OF ANGIOSPERM FAMILIES (BIOB 518) Belay Melese (Assist. Professor)
  2. 2. Module Contents 1. The Angiosperms, objectives of angiosperm taxonomy and the development of taxonomic thoughts 2. Principles and practice of angiosperm taxonomy, hierarchical categories of angiosperms, nomenclature, taxonomic characters (vegetative and reproductive), Flora, field and herbarium techniques in angiosperm taxonomy, keys and the use of keys. 3. Classification of angiosperms into orders and families. 4. Description of selected angiosperm families
  3. 3. Learning outcomes: • Upon successful completion of the module, the learners will be able to: • Classify angiosperm plants into orders, families and lower categories of the hierarchical system. • Identify unknown angiosperm plant family by making use of keys, illustrations and descriptions of plants treated in Flora of Ethiopia and Eritrea as well as other sources of botanical literature. • Identify unknown flowering plants by comparing them with authenticated plant species housed at the National Herbarium and other herbaria.
  4. 4. • Make use of scientific names of angiosperm plants and discuss issues relating to angiosperms plant resources and knowledge of angiosperm plants, and • Understand the importance of flowering plants as sources of food, medicine, timber, fuel wood, conservation and management of plant resources. • Using angiosperm taxonomic methods and applying the knowledge in the areas of conservation, biodiversity studies, as well as agriculture and traditional medicine.
  5. 5. PART 1 1. THE ANGIOSPERMS Introduction What is the position that Angiosperms occupy in the Plant Kingdom and how are they distinguished from the other major divisions?
  6. 6. 1.1.3. Classification of the Tracheophyta The Division Tracheophyta is subdivided into the following subdivisions. • S.d. Psilophytina (Psilopsida) - Psilopods • S.d. Lycophytina (Lycopsida) - Lycopods, Selaginella, Isoetes • S.d. Sphenophytina (Sphenopsida) – Equisetum • S.d. Filicophytina - Ferns • S.d. Spermatophytina - Angiosperms, Gymnosperms
  7. 7. 1.1.2. Characteristics of the Division Tracheophyta Habitat: Predominantly terrestrial or epiphytic Pigments: Chlorophylls a and b, carotenoids Food reserves: Starch to a lesser extent fats, insulin and other polysaccharides, proteins Cell wall components: cellulose, hemicellulose, lignin Reproduction: Heteromorphic life cycle; sporophyte the conspicuous phase - Sex organs with or without a jacket of sterile cells - Spores with well-defined wall (exine) impregnated with sporopollenin. - Spores often two sizes, the larger (mega spores) female and smaller (microspores) male - heterospory Growth forms: Predominantly axial
  8. 8. The Angiosperms The angiosperms with over 300,000 living species are the larger component of the earth's vegetation. They are nevertheless recent in their evolution and their dominance is comparatively recent.
  9. 9. I. Class Gymnospermopsida - Gymnosperms - Ovules naked, not enclosed by an ovary, receiving pollen grains (microspores) directly on the micropyle mainly by wind. - Pollen grains with bladder like extension of the outer coat. - Cotyledons two or several, rarely one by supression. - Wood (except Gnetaceae) with no true vessels. Trees and shrubs, mainly with needle like leaves. - Flowers unisexual & pollination mainly by wind e.g Podocarpus, Juniperus, Cuppressus
  10. 10. II. Class Angiospermopsida: Angiosperms - Ovules enclosed in an ovary usually crowned by a style and stigma, the style receiving the pollen grains (microspores) mainly by insects, or wind when much reduced. - Wood consisting true vessels. Trees, shrubs and herbs, more recent than gymnosperms. - Flowers bisexual or unisexual. - The Class Angiospermopsida is further subdivided into two classes: • Dicotyledonaeae and Monocotyledonae.
  11. 11. Subclass Dicotyledonae A. Dicotyledones - Embryonic plants with 2 cotyledons (seed leaves). - Vascular bundles of the stem usually arranged in a circle (except few genera in herbaceous families with scattered vascular bundles e.g. Piper in Piperaceae). - Leaves typically net veined, opposite or alternate. - Flowers usually 5 or 4 merous
  12. 12. i. Archichlamydeae: Groups of plants with -petals free from each other Polypetalae -petals absent Apetalae -rarely united at the base ii. Metachlamydeae: a group of Dicotyledoneae comprising plants in which the petals of the flowers are united. -petals united into a tube Gamopetalae/Sympetalae iii. Monochlamydeae: Groups of plants where -petals are not differentiated into petals and sepals.
  13. 13. i. Subclass Monocotyledonae - Monocotyledones: - Flowers usually trimerous. - Embryonic plant with 1 cotyledone (seed leaf). - Vascular bundles of the stem closed or scattered. - Leaves typically parallel nerved (veined) and alternate.
  14. 14. 1. 2. Objectives of Angiosperm Taxonomy The purpose of angiosperm taxonomy, thus, is to develop a system of classifying the angiospermous plants in a way that all their differences and similarities are set out in an ordered manner.
  15. 15. Taxonomic practise includes: Classification is the ordering of organisms into groups or sets on the basis of their relationships i.e of their association, configurity, similarity or all of these. It is also defined as the process of establishing and defining systematic groups known as taxa. Nomenclature is the system of naming organisms. - the allocaton of names to the taxa produced. Classification precedes naming. Identification is a process of placing individual organisms into classes that have been establised a priori.
  16. 16. 1.3. THE DEVELOPMENT OF TAXONOMIC THOUGHT 1.3.1. FOLK TAXONOMY Such practices is being done by nearly all cultures in which the community puts some order into the plant life. Some of the systems of naming plants are based on the perceived relationships among the plants. e.g. ‘Sar’ in amharic refers to most species of grasses; ‘Grar’ in amharic, ‘lafto’ in oromo refers to many Acacia sp. ‘Ret’ in amharic, ‘ere’ in tigray, ‘ourgessa’ in oromo, ‘egedel’ in guragigna refers to almost all species of Aloe occurring in that area . ‘Atat’ (amharic, tigrigna, & guragigna), ‘kombolcha’ in oromo laguages refers to the genusMaytenus.
  17. 17. In general, in folk taxonomy, recognition of taxonomic relationships are demonstrated at the generic and infra-generic levels. Infact as demonstrated above, folk taxonomy is almost in close correspondence at the generic level. Some times, there is a close correspondence at the species level. This is mainly when the species is economically important. For example: -Eragrostis teff is known as Tef (Am; Tig) ;Tafi (Oromo; Gur) -Guizotia abyssinica Nug (Am.) -Ensete ventricosum Enset (Am); Eset (Gu.); Kocho (Or.); Outa (Wel.); Weise (Kembatta)
  18. 18. 1.3.2. FROM ARISTOTLE TO NEW SYSTEMATICS The study of plant classification is believed to have had its roots among the Greeks, particularly Aristotle (384 -322 B.C.) and some of his students such as Alexander the Great and Theophrastus (370 287 B.C.). - From the time of Aristotle to the present, three lines of thought can be discerned in plant classification: -essentialism (Artificial) - empiricism (Natural) - Evolutionism
  19. 19. Basically, essentialism and empricism are pre- Darwinian concepts (i.e occuring before the publication of the origin of species by Charles Darwin in 1959). - While evolutionism is post-Darwinian. The three thoughts were not in clear-cut compartments. As seen in practice, there were some evolutionist ideas before Darwin and a considerable of essentialist and empiricist thoughts in today's taxonomy.
  20. 20. ESSENTIALISM (= ARTIFICIAL CLASSIFICATION) Essentialism in taxonomic practice and the thought is derived from Aristotelian logic which is based on the belief that “an object or a thing has certain attributes (its essence) that make it what it is”. Were basically intuitive concepts and made taxonomy largely a subjective science- full of a priori considerations i.e. certain attributes have more importance or are given more weight than other attributes. Thus, this approach gives more weight to certain morphological characters (features) than others. Theophrastus, Caesalpinus, Linnaeus and De Candolle were well known essentialists.
  21. 21. Theophrastus (c.370 - 287 B.C.) -He classified plants primarily based on their habit (trees, shrubs or herbs) or whether they were cultivated or wild. -He also had recognized certain diagnostic criteria such as the fusion or separation of parts, types of inflorescences and position of the ovary in relation to the other floral parts. Caesalpinus (1519-1603): -He also classified plants based on their habit. He also recognized the importance of seeds and fruits in classification. -He recognized groups that correspond to families su as the Cruciferea (Brassicaceae), compositea and Leguminosea.
  22. 22. Carl Linnaeus (1707-1778) He based his classification on sexual character. - Linnaeus divided seed plants into 23 classes based on the number and arrangement of the stamens. -The classes were subdivided into orders on the basis of the number of their styles. -He published the Genera Plantarum in 1737 and the Species Plantarum in 1753.
  23. 23. Candolle (1778-1841) • His classification was based on certain important characters only; thus, essentialists. • He also emphasized the importance of constant characters in taxonomic practice.
  24. 24. EMPIRICISM ( = NATURAL CLASSIFICATION) • The system is a „natural system‟ which uses as many characters as possible in classification without assuming, a priori considerations, importance of certain characters. The best known empiricists before Darwinian period were John Ray and Michael Adanson. John Ray (1628 - 1705) established the concept that “all parts of a plant are used in classification”.
  25. 25. • He recognized • Michael Adanson (1727 - 1806) Devised a natural system using as many characters as possible without giving weight to any of them a priori
  26. 26. 1.3.3. Post Darwinian Taxonomy (Phylogenetic Systems) Charles Darwin (1809 - 1882) - Published „The Origin of Species‟ in 1859. - Based on his observation, - Organisms competing for limiting factors in the environment Some of the organisms will survive the competition - Survival of the fittest. - The constant struggle for survival leads to evolution, i.e gradual and cumulative adaptive changes.
  27. 27. • In phylogenetic systems plant families are arranged according to presumed relationships by descent. • There are two major schools of thought on phylogenetic systems. • The two schools differ because of their concept of nature of presumed primitive angiosperm flower. • The two schools were: -the Englerian school -the Ranalian school.
  28. 28. The Englerian School The Englerian school was started by Adolf Engler (1844 - 1930) (after whom the system was based) and Karl Prantl (1849 - 1893). The system was a modification of Eichler (1839 - 1887). According to this system: Primitive flowers are: unisexual wind pollinated Monochlamydeous (with perianth not differentiated into petals & sepals) Examples of families with these attributes are: Urticaceaae Casuarinaceae Piperaceae
  29. 29. The Ranalian School of Thought - This school was originated by C.E. Bessey (1847 1915) [The Phylogenetic taxonomy & Flowering Plants] who based his work on G. Bentham (1800 1884) & J. D. Hooker (1817 1911). The primitive (ancestoral) flowering plants are - hermaphroditic (bisexual) - entomophilous (insect pollinated) - numerous stamens and carpels Examples of this school Ranales (order) Ranunculaceae Papaveraceae Magnoliaceae, etc
  30. 30. Both the Englerian & Ranalean school agree on: - An inferior ovary is more advance than superior ovary. - Gamopetaly (fused petals) is more advanced than Polypetaly (separate petals). The Flora of Ethiopia is following Hutchison that follows the Rannealean school of thought.
  31. 31. 2. PRINCIPLES AND PRACTICE OF TAXONOMY 2.1. INTRODUCTION Characters provide the taxonomic evidence for natural classification in the Adansonian sense and a large part of the evidence for evolutionary (“ Phylogenetic”) classification. • Although it is organisms (or life cycles of organisms), which are classified, it is their characters, which provide the evidence used in classification. • Ideally the whole organism (i.e. all its attributes) should be employed, but since each individual possesses thousands of potential characters, practical limitations impose a restriction on the numbers used.
  32. 32. Character: Any attribute (or descriptive phrase) referring to form, structure or behavior that helps to be used for two main activities of taxonomy: a)identification and characterization the taxonomist seeks to employ diagnostic or key characters, i.e. those of limited occurrence, selected so that their use alone is sufficient for reaching a correct diagnosis; b)Grouping (classification) of these species into higher taxa (natural groups), i.e. into a system that as far as possible expresses their natural relationships.
  33. 33. 2. Character types 2.2.2. Qualitative and Quantitative Characters - Qualitative: Characters relating to form such as opposite verses alternate leaves, shape, color, hairiness and indumentum (presence or absence). Quantitative: Assessment by number, size, length, etc.
  34. 34. 2.3 Sources of Taxonomic Evidences Characters can be drawn from any part and phase of development of the plant. 2.3.1. Morphology and Anatomy Morphological features have the great advantage that we can see them easily and can therefore appreciate their variability with much more facility than we can with other kinds of features.
  35. 35. A. Vegetative characters i. Habit. It is much easier to recognize habit than to describe it in many instances. ii. Underground organs. The underground parts of the plant often provide valuable characters for taxonomic discrimination, yet they frequently do not receive the attention they deserve due to bad collecting. The form of the root structure is widely employed in the taxonomy of the genus Ranunculus.
  36. 36. iii. Leaves. Leaf characters are extensively employed for the recognition of species. - Simple or compound - Arrangement - Attachment - Shapes - Margins - Apex - Bases
  37. 37. Leaves
  38. 38. iv. Indumentum. Great diversity is shown in the indumentum of many groups, which has often-great taxonomic significance.
  39. 39. b. Reproductive characters. Angiosperm classification is traditionally based on the mature plant in its reproductive phase. Yet genetic differences and resemblances can find expression at any stage in the life cycle, and may be vital selective value in the seedling stage. Inflorescences. The inflorescence provides useful characters in many genera
  40. 40. Inflorescence types
  41. 41. • Solitary: A single flower on a caulescent or acaulescent stem. • Spike: Unbranched inflorescence with sessile flowers (no pedicels). • Raceme: Unbranched inflorescence with flowers on pedicels. • Panicle: A branched or compound raceme (i.e. main rachis with branches bearing flowers on pedicels). • Corymb: Flat-topped inflorescence with youngest flowers at the end of main axis or rachis. • Cyme: Flat-topped inflorescence with oldest flowers at the end of main axis. [Includes simple, compound and scorpioid cymes.] • Umbel: Flat-topped inflorescence with all the pedicels arising from a common point. [Includes simple and compound umbels.] • Catkin or Ament: A spike-like inflorescence of unisexual, apetalous flowers, often pendent and falling as a unit. This is the typical inflorescence of willow (Salix), • Spadix: A thick, fleshy spike of unisexual, apetalous flowers, often surrounded by a vase-shaped or funnel-like modified leaf or spathe which is often brightly colored. The male flowers are typically clustered above the female flowers on an erect, phallus-like spike. This is the characteristic inflorescence of the arum family (Araceae).
  42. 42. Description of Floral parts • Description of Flowers: Corolla
  43. 43. Description of Flowers: Stamens
  44. 44. Description of Flowers: Pistils
  45. 45. Flower and Fruits Placentation
  46. 46. Fruits and Seeds. Comparative seed morphology
  47. 47. b. Anatomical Characters • Anatomical characters play an increasingly important role in the formulation of natural or phenetic groups.
  48. 48. 2.3.2. Biochemical characters (Information to be collected by students) 2.3.3. Physiological characters (Information to be collected by students) 2.3.4. Cytological characters (Information to be collected by students) 2.3.5. Geographical (Information to be collected by students)
  49. 49. 2.3.6. Palynology and Embryology Pollen Morphology and Taxonomy Taxonomists have been prone to overlook pollen morphological characters although they were fully appreciated in the past. Erdtman published a treatise on pollen analysis in 1943, and in 1952 the first part of his manual pollen Morphology and plant Taxonomy, dealing with the Angiosperms appeared.
  50. 50. Characters of the pollen and their role in taxonomy. The main characters of taxonomic value in pollen grains are: - number and position of furrows - Monocolpate: these are provided with a single furrow, which develops on one side of the grain remote from the point of contact in the tetrad - Tricolpate: these have three furrows. - number, position and complexity of the apertures, and the form of sculpturing of the exine. - Variation is also shown in size and general shape.
  51. 51. 3. Units of Classification 3.1. Species Taxonomic Species Concept It is “the assemblages of individuals with morphological features in common and separable from other such assemblages by correlated morphological discontinuities in a number of features”. Biological Species Concept The biological species concept rest on the contention that there are objective discontinuities in nature which delimit the units we should recognize as species. These discontinuities are caused by restriction of gene flow between actually or potentially interbreeding populations.
  52. 52. a) Subspecies The category subspecies is recognized as major morphological subdivisions of the species followed by geographical separation E.g. Maytenus gracilipes subsp. arguta and subsp. gracilipes - How are subspecies formed? - In the process of speciation, they are regarded as incipient (beginning) species. - In the process where originally distinct species are coming together and fusing.
  53. 53. b. Varieties Like the subspecies, the variety has been employed in several senses. It is widely used today for local facies of species morphologically distinct and occupying a restricted geographical area. E.g. Maytenus arbutifolia var. sidamoensis. Emphasis is on the small scale, more localized range of the variety, compared with the large- scale, regional basis of the subspecies.
  54. 54. Genus Three questions to be asked while deciding on generic concepts: (1) Is the group a natural one, and if not is it possible to make it so? Monophyly, in modern taxonomy is often deduced by means of genetic and geographical information in relation to morphology and is very helpful in deciding where the line should be drawn between two genera. (2) Where should the line be drawn between closely related genera? If our classification is to be natural, the modern taxonomist should be guided “not by a single arbitrary or artificial character but by the sum total of characters. (3) Is it practicable to recognize the group as a separate genus, or would it be better included in another?
  55. 55. Family - Many of the considerations made for genera also apply with equal force to the families. - Families should be natural and, where practicable, evidently monophyletic. - As with the genus, vegetative characters may serve to delimit them as effectively as flower and fruit together. - Floral characters generally provide useful morphological characters than do the vegetative organs. - But note that underground parts provide useful characters for the natural divisions in monocots.
  56. 56. Families There are, broadly, two kinds of families recognized today-“definable” and “indefinable”. Definable families are those which are obviously very natural ones, like Cruciferae, Umbelliferae, Acanthaceae and Gramineae, and which are clearly delimited. The “indefinable” families are represented by the Ranunculaceae, Berberidaceae, Rosaceae where a great diversity of structure (floral and often vegetative) is found.
  57. 57. Order - The most unsatisfactory taxon in Angiosperm classification is the order (“Cohort”, usually ending in -ales) into which families are grouped. - Most of these are extremely difficult to define and the naturalness of many of them are questionable. - Most of them are of little use as an aid in identification. - This category serves no more than to accommodate what each taxonomist believes to be a natural or convenient group of families.