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 themegasporangia in carpels.
3 FlowerREPRODUCTIVE 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” withtissues capable of undergoing meiosisSPOROPHYLLS – those modified leaves with meiotic capacity.- Microsporophylls – stamens – produce pollen in anthers- Megasporophylls – carpels – produce eggs in ovules
10 Evolution of the Androecium DERIVED FROM MODIFIED LEAVES- Microsporangia (meiosis microspores pollen grains) on lamina originallyINCREASING LEVELS OF REDUCTION- Lamina becomes filament- Sporangial tissue becomes anther wall- Provides for release of pollenCAN BE IN A SINGLE WHORL OR MULTIPLE WHORLS- Tremendous variation in flowering plants.- Often associated with specific type of pollinator.
14 Evolution of the Carpel MODIFICATION OF MEGASPOROPHYLL- Evolution of megasporophyll structure traced back to seed ferns – 200 to 300 mybpLEAF 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) = gynoeciumFUSION OF CARPELS- Unfused (separate) carpels - apocarpous- Fused (united) carpels - syncarpousPOSITION 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 integumented megasporangium The Ovule =integumented megasporangiumsporangiumfemalegametophyte(derivedfrom a singlespore)integumentsmicropyle
17 Folding of one megasporophyll S = suture; formed by fusion of leaf Folding of megasporophyll to form simple carpelFolding of onemegasporophyllS = suture; formedby fusion of leafmargins; receptiveto pollenreceptacle
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 flowerstructures.
40 Merosity = basic number of parts in each whorl-3 sepals, 3 petals, 6 stamens, 3 carpels = 3-merous(or trimerous)-4 sepals, 4 petals, 6 or 8 stamens, 2 or 4 carpels =4-merous (or tetramerous)-5 sepals, 5 petals, 5 or 10 stamens, 3 or 5 carpels =5-merous (or pentamerous)
41 Interpretation of Floral Structures OBSERVE STRUCTURES IN EACH WHORL- How many whorls are there?- How many parts are present in the calyx? Corolla? - Describe the androecium, then the gynoecium.DETERMINE POSITION OF THE FLOWER PARTS RELATIVE TO THE OVARY- Hypogynous? Perigynous? Epigynous? Epiperigynous?GYNOECIUM- Apocarpous? Syncarpous? If so, how many carpels?- Position? Superior or inferior or half-inferior?- Placentation?ADNATION or CONNATION?- Fusion of floral parts can sometimes be diagnostic.UNUSUAL OR REMARKABLE FLORAL STRUCTURES?- Specializations for pollination?