1 / 40

Flowers and Their Evolution

Flowers and Their Evolution. Spring 2012. Flower = a short, determinate shoot bearing highly modified leaves, some of which are fertile (i.e., bearing either microsporangia or megasporangia ), with the microsporangia in stamens and the megasporangia in carpels . Flower.

darena
Download Presentation

Flowers and Their Evolution

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Flowers and Their Evolution Spring 2012

  2. Flower = a short, determinate shoot bearing highly modified leaves, some of which are fertile (i.e., bearing either microsporangia or megasporangia), with the microsporangia in stamens and the megasporangiain carpels.

  3. Flower • REPRODUCTIVE STRUCTURE – Evolutionary requirement to reproduce by sexual means. Pollen transfer and seed dispersal needed. • MODIFIED FOLIAR APPENDAGES – all function together to form the reproductive organ known as the FLOWER. • MODIFICATIONS OF LEAVES – All floral organs are modified LEAVES. Four terminal WHORLS of modified leaves: - Two outermost whorls (sepals, petals) are sterile (non- meiotic tissues) - Two innermost whorls (sporophylls) are “fertile” with tissues capable of undergoing meiosis • SPOROPHYLLS – those modified leaves with meiotic capacity. - Microsporophylls – stamens – produce pollen in anthers - Megasporophylls – carpels – produce eggs in ovules

  4. Fig. 6.2 from Simpson

  5. Floral Whorls • Attached to RECEPTACLE • Sepals (collectively the Calyx) • Petals (collectively the Corolla) • Stamens (anthers + filaments) Androecium (andros = male; -oecium = house) • “Pistil” – carpel(s) [fused or not] Gynoecium (gynos = female; -oecium = house)

  6. Floral Parts: Major whorls pistil (1-many carpels) - gynoecium stamens - androecium petals - corolla sepals - calyx receptacle

  7. stamen pistil Sepals and petals are relatively leaf-like. sepal young leaves flower bud petal

  8. “ABC” Model of Floral development Fig. 6.5 from Simpson

  9. Floral Anatomy

  10. Evolution of the Androecium • DERIVED FROM MODIFIED LEAVES - Microsporangia (meiosis  microspores  pollen grains) on lamina originally • INCREASING LEVELS OF REDUCTION - Lamina becomes filament - Sporangial tissue becomes anther wall - Provides for release of pollen • CAN BE IN A SINGLE WHORL OR MULTIPLE WHORLS - Tremendous variation in flowering plants. - Often associated with specific type of pollinator.

  11. Stamen evolution laminar stamens

  12. Fig. 9.26 Fig. 9.25

  13. Floral Anatomy

  14. Evolution of the Carpel • MODIFICATION OF MEGASPOROPHYLL - Evolution of megasporophyll structure traced back to seed ferns – 200 to 300 mybp • LEAF WITH MARGINAL MEIOTIC ZONES FOLDS - Ovules located at margins of sporophylls. - Lamina curves inward (toward the floral axis - adaxially) - Carpel is formed by folding – conduplicate - Margins fuse, enclosing ovules - Carpel(s) = gynoecium • FUSION OF CARPELS - Unfused (separate) carpels - apocarpous - Fused (united) carpels - syncarpous • POSITION OF THE GYNOECIUM relative to other floral whorls is important in describing floral structures. • PLACEMENT OF OVULES (placentation) within the gynoecium is also important; shows evolutionary origins of the carpel.

  15. The Ovule = integumented megasporangium sporangium female gametophyte (derived from a single spore) integuments micropyle

  16. Carpel evolution (Ovules) (megasporophyll)

  17. Folding of megasporophyll to form simple carpel Folding of one megasporophyll S = suture; formed by fusion of leaf margins; receptive to pollen (Receptacle located below)

  18. Carpel evolution stigma stigmatic crest

  19. Fig. 9.30 from Simpson

  20. Simple Carpel – One Pistil

  21. Apocarpy – Separate Carpels = 5 pistils in this example

  22. Apocarpous gynoecium – Ranunculus sp. with many pistils elongated receptacle

  23. Liriodendron Magnolia

  24. Fig. 9.31 from Simpson

  25. Syncarpousgynoecium – One pistil, 3 carpels

  26. Various gynoecia – Apocarpousvs.Syncarpous (Hint: stigma number usually = carpel number)

  27. Syncarpy – How many carpels? Locules?

  28. Adnation: Fusion of different parts Stamens adnate to petals

  29. Connation: Fusion of similar parts Fusion of filaments into a staminal tube

  30. Ovary position relative to other parts The hypanthium requires both connation and adnation. Fig. 9.32 from Simpson

  31. Ovary superior Parts hypogynous Citrus sp.

  32. Ovary superior, parts perigynous (floral cup or tube = hypanthium present) Rosa sp.

  33. Ovary inferior, parts epiperigynous (hypanthium present) Fuchsia sp.

  34. Ovary inferior, parts epigynous Vaccinium sp.

  35. Ovules and Placentation • OVULES CONTAIN THE MEGAGAMETOPHYTE - Provides for fertilization of egg cell in megagametophyte and protection during development. - Ovule matures into the SEED. • ATTACHMENT OF THE OVULES VIA FUNICULUS - Analogous to the mammalian “umbilical cord” - Point of attachment on inner ovary wall is the PLACENTA - Can vary depending on type of flower. • PLACENTATION IS OFTEN DIAGNOSTIC - Plant families typically have one placentation type. - Often best seen with cross section through ovary. • PLACENTATION REFLECTS EVOLUTIONARY DEVELOPMENT - Fusion of carpels, presence of vascular bundles, etc. can support hypotheses about evolution of particular flower structures.

  36. Fig. 9.33 from Simpson

  37. Fig. 9.33, Part A only

  38. Placentation Axile Parietal

  39. Floral Symmetry Radial Bilateral Actinomorphic Zygomorphic

  40. Interpretation of Floral Structures • OBSERVE STRUCTURES IN EACH WHORL - How many parts are present in the calyx? Corolla? - Describe the androecium, then the gynoecium. • DETERMINE CONDITION OF THE FLOWER - Hypogynous? Perigynous? Epigynous? • GYNOECIUM - Apocarpous? Syncarpous? If so, how many carpels? - Placentation? Position of stigma relative to other parts. • ADNATION or CONNATION? - Fusion of floral parts can sometimes be diagnostic. • UNUSUAL OR REMARKABLE FLORAL STRUCTURES? - Specializations for pollination?

More Related