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Origins of Angiosperms - PowerPoint PPT Presentation

JasminFlorian
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Origins of Angiosperms

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  1. Origins of Angiosperms Spring 2010

  2. Outline • Origin of the angiosperms • Characters of angiosperms • Brief history of angiosperm classification • Major groups of angiosperms • ANITA grade

  3. Origin of the Angiosperms

  4. Conifers Gnetophytes Ginkgo Cycads Angiosperms ? Progymnosperms (“seed ferns”) Divergence estimated at ca. 325 mybp

  5. Geologic Time

  6. Timing of Angiosperm Divergences • The timing of the origin of the angiosperms still is uncertain, but most would agree on a Triassic or Jurassic initial divergence, although there is no unequivocal fossil evidence • A demonstrable “burst” of phylogenetic radiation is found in the fossil record beginning in the mid- to-late Cretaceous, 140 - 100 mybp

  7. Figure 7.16 from the text

  8. Origin of the Angiosperms • pollen grains from ca. 140 mya (early Cretaceous) but already major radiation! • earliest flowers 130 mya • likely no extant group of seed plants is very closely related to the angiosperms!

  9. Origin of Angiosperms • Cycad-like plants: Bennettitales? • large, flowerlike strobili: • pollen-producing organs surrounding an axis bearing naked ovules/seeds

  10. Origin of Angiosperms Modification of a “seed fern” such as Caytonia? Caytonia fossil: ovule

  11. Origin of Angiosperms • Archaefructus • ca. 130 mya • ancestral flowering plant or • extinct off-shoot of an extinct lineage? • aquatic plant (dissected leaves) • elongate reproductive axes: • -paired stamens below • -several-seeded carpels above

  12. Characters of Angiosperms

  13. Angiosperms (Flowering Plants) “Dicotyledons” Magnoliids Monocots Eudicots -- likely evolved WITHIN angiosperms Reduced male and female gametophytes! ALSO: -- nonmotile sperm! (evolved independently in certain non flowering taxa)

  14. What makes a plant an angiosperm? • Flower (usually with perianth) • Carpels with a stigmatic surface for pollen germination; ovules enclosed within carpels; fruit • Ovules with two integuments • Reduced female gametophyte, usually 8 nuclei in 7 cells – no archegonium • Double fertilization with the production of 3N endosperm • Stamens with two pairs of lateral pollen sacs (microsporangia) • Xylem – most with vessels (evolved within angiosperms) • Phloem – sieve tube members with 1 or more companion cells derived from the same mother cell

  15. Flower Figure 4.16 from the text

  16. Spiral undifferentiated perianth parts = tepals (plesiomorphic)

  17. Differentiated sepals and petals (each in whorls) (apomorphic)

  18. Laminar stamens in basal angiosperms paired pollen sacs connective microsporangium filament

  19. Early carpel with stigmatic crest… Figure 4.19 from the text Figure 4.20 from the text …to the derived carpel with a style and an apical stigma.

  20. Female gametophyte in angiosperms -no waiting time as in gymnosperms! -note 2 integuments (bitegmic; some angiosperm lineages have lost one integument) -gymnosperms have only 1 integument (unitegmic) mature ovule ovule

  21. Seed development in angiosperms -no waiting time as in gymnosperms! double fertilization seed

  22. Avocado (Persea, Lauraceae) flower exocarp mesocarp endocarp seed fruit

  23. Vessels in Angiosperms • are the water (solute) conducting cells of the • xylem in most angiosperms • ends of cells have openings (perforation • plate), cells shorter and wider • more efficient, faster rate of flow but more • susceptible to air bubbles (embolisms) than • tracheids are • may have arisen independently in two or more • angiosperm lineages but may have had a • single origin

  24. Origin of vessels from tracheids Figure 4.32 from the text

  25. Angiosperm phloem • sieve tube members + companion cells • stm = specialized sugar-conducting • cells of the phloem of angiosperms; • lack a nucleus at functional maturity • cc = parenchyma cells associated • with stm • -function to load/unload sugars into stm cavity • -derived from the same mother • cell as its stm stm

  26. Brief history of angiosperm classification

  27. Alternative ways of thinking about early angiosperm characters… • “Old” School (German) - Engler - “Simple is primitive” (Few floral parts) - Ancestors are conifers - Pollination by wind - Modern relicts = “Amentiferae” (catkins) • “New” School (American) – Bessey - “Flowers with many parts are primitive” - Ancestors are Cycad-like plants - Pollination by primitive insects - Modern relicts = Magnolias and allies

  28. Heinrich Gustav Adolph Engler(1844-1930) • German Botanist at Berlin Botanical Garden-Was the primary European in interpreting the grouping of major angiosperm assemblages-“Few simple flower parts primitive”-Small, unisexual flowers primitive

  29. Englerian ‘Primitive Taxa’ Juglans sp. Quercus sp. “Amentiferae” Betula sp.

  30. Charles Edwin Bessey(1845-1915) -Botanist at Iowa State University from 1869-1884 (left in 1884 to teach in Nebraska)-Was a “major player” in interpreting and understanding angiosperm evolution-“Many flower parts primitive” Bessey Hall Iowa State University

  31. Bessey’s “Cactus” (1915) Placed plant groups with many floral parts in a basal position as the ‘ancestral’ forms. Outlined ‘dicta’ for the construction of phylogenies using the evolutionary trends in character changes. Polypetalous flowers, insect pollination, cycad-like ancestors

  32. Besseyan ‘Primitive Taxa’ Nymphaeaceae Magnoliaceae

  33. Figure 7.16 from the text

  34. Major Groups of Angiosperms • Basal Angiosperms (ANITA grade) - Amborellaceae - Nympheaceae - Illiciaceae • Magnoliid Complex (incl. “paleoherbs”) - Magnoliales - Piperales - Winterales • MONOCOTS • EUDICOTS (tricolpates)

  35. Major Groups of Eudicots • Basal Tricolpates - Ranunculales and allied families • Caryophyllales & Saxifragales • Rosid Clade - Basal Rosids - Eurosids I (Fabids) - Eurosids II (Malvids) • Asterid Clade - Basal Asterids - Euasterids I (Lamiids) - Euasterids II (Campanulids)

  36. ANITA grade • Amborella (Amborellales) • Nymphaea (Nymphaeales) • Illicium (Austrobaileyales) • Trimenia (Austrobaileyales) • Austrobaileya (Austrobaileyales)

  37. ANITA grade Figure 9.1 from the text > 125 mybp Grade = a polyphyletic (or paraphyletic) group whose members share a similar level of morphological or physiological complexity. > 140 mybp

  38. Major Angiosperm Clades Amborellaceae Nymphaeales Austrobaileyales MAGNOLIID COMPLEX MONOCOTS EUDICOTS [TRICOLPATES] “BASAL FAMILIES” Soltis et al. 2000, APG II 2002, Judd et al. 2002

  39. Basal Angiosperms: Amborellaceae • New Caledonia • Understory shrub; plants dioecious • 1 species (monotypic): Amborella trichopoda • Leaves simple, evergreen • Flowers small, unisexual: ♀ apocarpous, with stigmatic crests; ♂ with laminar stamens • Significant features: Most basal of all flowering plants; no vessels in wood • Special uses: (none)

  40. Basal Angiosperms:Amborellaceae (Amborella Family) Amborella trichopoda

  41. Basal Angiosperms:Nymphaeaceae(Water Lily Family) • Widespread, tropics to temperate regions • Aquatic rhizomatous herbs, sap milky • 70 species; 8 genera • Flowers: many parts; laminar stamens; “floating”; colorful perianth; “beetle” syndrome • Special uses: ornamentals; sacred lotus • Required taxa: Nymphaea (water lily)

  42. Basal Angiosperms:Nymphaeaceae (Water-lily Family) • numerous petals, stamens, carpels • laminar stamens • pollen monosulcate • stigma discoid, radiating • berry-like fruit, dehiscent • perisperm • usually lack vessels (or have tracheid-like vessels)

  43. Nymphaea odorata – Water Lily

  44. Nymphaea tuberosaWater Lily

  45. NupharWater Lily

  46. Victoria amazonica – Giant Water Lily

  47. Basal Angiosperms:Illiciaceae(Star Anise Family) • SE Asia, SE USA and Caribbean • Trees and shrubs • 1 genus, Illicium; ca. 40 species • Flowers: many floral parts/tepals; 1 ovule/carpel • Special uses: star anise (spice) • Required taxa: (none)

  48. Illicium – Star Anise Illicium parviflorum Illiciumfloridanum

  49. As we venture through the various major groups of angiosperms… • Identify the plesiomorphic characteristics associated with particular groups and note their apomorphies (if any) as well. • Try to associate “syndromes” of characteristics with each group (make note of special characters occurring together). • One good way to study is to write keys to the groups we cover in any given unit. • Names of groups are important! Learn to spell and say them! • Ask questions!!