Evolution of the Flower Chapter 20Slide 2Review of Flower StructureSlide 4Slide 5Evolution of the CarpelSlide 7Derived Features of AngiospermsSlide 9Origin of the AngiospermsSlide 11Pollination and Seed DispersalSlide 13Monocots or Eudicots?Evolution of the flowerParts of the flower provide clues to evolutionSlide 17In most angiospermsSlide 19The StamensSlide 21Slide 22Slide 23Stamens continueSlide 25Stamens can become nectariesThe CarpelsFour evolutionary trends among flowers are evidentThe Asteraceae and Orchidaceae are examples of specialized familiesThe flower of the Asteraceae are closely bunched together into a headComposite flowersSlide 32PappusOrchidaceae is the largest Angiosperm familyOrchidsSlide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Animals serve as the primary agents of floral evolutionSlide 44Slide 45Slide 46Slide 47Slide 48Wind pollination flowers produce no nectarFruit is a Mature ovarySlide 51Simple fruitsSimple fruit fleshy fruitsSlide 54Dry simple fruitSlide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Evolution of the FlowerChapter 20•Two classes - Monocotyledons and Dicotyledons •Distinctive reproductive feature - carpels •Angiosperms enclose their seeds in structures known as carpels, instead of lying naked on the scales of a strobilus as in gymnosperms. Hence the name "angiosperm" which means "seed in vessel".Review of Flower Structure •Flowers are reproductive structures that are formed from four sets of modified leaves on a shortened stem. In other words, the flower is a modified strobilus. •Sepals - protect floral parts in the bud •Petals - attract pollinators •Stamens - anthers and filaments •Carpels - stigma, style, and ovary (collection of carpels referred to as a pistil) •The carpel is a unique structure found only in angiosperms.–Cut into the pistil and you will see one or more tiny chambers, each chamber holding one or more sporangia on tiny stalks. –These sporangia are the ovules - each carpel can hold one or several ovules –Ovules in the ovary develop into seeds •The ovary wall forms a fruit to help disperse the seeds •There is an amazing diversity of floral structures. Linnaeus used these differences to classify plants.Evolution of the Carpel•Goethe, German writer, philosopher, and (in his spare time) noted botanist, proposed in 1790 that carpels evolved from leaves. •Chambers in the pistil were probably formed from a sporophyll - a fertile leaf bearing ovules. •Sporophyll had ovules (modified sporangia) on its outer edges. •Edges of the leaf folded over and fused together to form a protective chamber - the carpel.•Pistils probably formed by the fusion of several carpels along the midrib of the modified leaves. •Goethe's "foliar theory of the carpel" is still the best hypothesis for explaining the evolution of the carpel.Derived Features of Angiosperms •Leaves with finely divided venation •Complex xylem - incl. vessels and parenchyma•Complex phloem - sieve tube elements w/companion cells •Herbaceous habit - rapid life cycle (some angios) •Ovary to protect ovules ("seeds in vessels") •Double fertilization and formation of triploid endosperm•Bisexual Flowers – microsporangia and megasporangia in same strobilus •Advanced pollination syndromes - insects, birds, etc. •Fruits to protect and diserse seeds •Extreme diversity in secondary metabolismOrigin of the AngiospermsDarwin called the origin of the angiosperms an "abominable mystery". •The evolution of angiosperms remains a mystery to this day, although great progress has been made in recent years solving this mystery using a combination of fossil evidence, molecular data, and the discovery of the primitive angiosperm Amborella. •Flowering plants evolved sometime during the Cretaceous, approximately 140 million years ago, while the dinosaurs were at their peak.•However, no fossils showing a transition from gymnosperm to angiosperm have been discovered. This makes the origin of the angiosperms mysterious. •Angiosperms quickly became the dominant plants, although gymnosperms continued to rule in cold, dry, or sandy habitats, as they still do today. •Regardless of the origin of the angiosperms, by the end of the Cretaceous (65-70 mya) most flowering plant families had evolved.Pollination and Seed Dispersal•Coevolution occurs when an evolutionary change in one organism leads to an evolutionary change in another organism that interacts with it. •Flowering plants show two great examples of coevolution: evolution of animal pollination and evolution of fruit dispersal. •Flowers that rely on wind pollination are tiny and inconspicuous (like oak trees, maple trees, corn, grasses). •Flowers that are pollinated by animals have showy petals to attract the pollinators.•Flowers advertise their reward of nectar, sugar water, to attract pollinators. •Fruits function to disperse seeds. –Animals eat fruit, but don't digest seeds. –Tiny hooks and spines to attach to animal. –Also dispersed by wind, water (coconuts).Monocots or Eudicots?•Some flowering plants are neither monocots or dicots.•MagnoliaEvolution of the flower•What were the flowers of the earliest angiosperms like?•Deduce their nature form what we know of certain living plants and from the fossil record. •In general flowers were diverse in the number of floral parts and in their arrangements.Parts of the flower provide clues to evolution•The perianth of early angiosperms did not have distinct sepals and petals•Sepals and petals were identical or there was a gradual transition in appearance between these whorls (magnolias and water lilies).•i.e. petals can be viewed as modified leaves that have become specialized for attracting pollinators.Wintergreen Chimphila umbellataIn most angiosperms•Petals were probably derived originally from stamens that lost their sporangia- becoming sterile and modified to new role•Most petals like stamens are supplied by one vascular strand•In contrast sepals are normally supplied by the same number of vascular strands in a leaf•Petal fusion resulting in a tubular corolla figure 20-8cThe Stamens•Magnoliids- broad, colored, and scented role in attracting floral visitors•In others- small greenish, fleshy•Many living angiosperm in contrast have thin filaments and thick terminal anthers•In stamens of monocots and eudicots are less diverse than MagnoliidsStamens continue•In some specialized