1 Angiosperms: Phylum Anthophyta, the flowering plants PDF
Preview 1 Angiosperms: Phylum Anthophyta, the flowering plants
Angiosperms: Figure 29.7 Land plant evolution. Phylum Anthophyta, the flowering plants 1. Overview of seed plant evolution 2. Traits of flowering plants a) Flowers b) Monocots vrs. Dicots 3. Pollination 4. The angiosperm life cycle Three variations on gametophyte/sporophyte relationships. Figure 30.3 Review: Development of a seed from an unfertilized ovule. The three most important new adaptations to land found in the seed plants are all shown in this diagram: 1. Very small gametophytes that are nourished by and protected inside the parental sporophyte (reduced even further in angiosperms) 2. Pollen grains, which provide protection and dispersal for the male gametophyte (often animal-dispersed in angiosperms) 3. The seed, which protects and disperses the new sporophyte embryo In angiosperms, female gamteophyte is reduced even further than in gymnosperms. (angiosperms: develop in flowers, dispersed in fruits) 1 Figure 30.12 Representatives of major angiosperm clades • Flowering plants used to be divided into two • Angiosperms groups: monocots and dicots – Are commonly known as flowering plants – Are seed plants that produce the reproductive • We now know that there are a number of structures called flowers and fruits different lineages that – Are the most widespread and diverse of all have the dicot morphology plants • Dicots are NOT monophyletic • Monocots are a monophyletic group http://www.tolweb.org/Angiosperms Figure 30.11 Archaefructus sinensis, a primitive flowering plant Angiosperm evolution • First angiopserms appeared ~ 240 mya • By the end of the mesozoic (~65 mya), angiosperms dominated many landscapes • Coevolution between plants and animals very important – Herbivores – Pollinators – Seed (often via fruit) dispersers 2 Amborella Magnolias • In one view, the most • The most primitive primitive angiosperm angiosperm has moderate resembled a Magnolia sized, perfect flowers, • Parts are spirally arranged • had large, showy, and have a moderate number unspecialized, spirally of parts. arranged flowers. • Floral evolution moves • No fusion of parts towards unisexual flowers, larger AND smaller flower • little differentiation of sizes, other perianth parts. arrangements, and larger AND smaller numbers of flower parts. Hypothesis f or the evolutionary origin of the carpel from a reproductive leaf (sporophyll) The ʻMostly Maleʼ hypothesis: • Angiosperms evolved from male gymnosperms • Pollen and ovule producing structures combined into a single flower: mutation • Mutation: ovules developed on some microsporophylls = carpels • Evidence: Flower development genes are similar to pollen producing gymnosperm genes • Position of ovules can be easily changed with mutations 3 Flowers Traits of angiosperms • A flower is a specialized shoot with modified leaves • Vascular seed plants that produce flowers – Sepals, which enclose the flower and fruits – Petals, which are brightly colored and attract • Extremely diverse: ~350,000 known species pollinators – Stamens, which produce pollen (compare to 720 gymnosperm spp.) – Carpels, which produce ovules • Xylem tissue not only has tracheids, but also Carpel Stigma fibers and vessel elements (except Stamen FilaAmnethnet r StyOlev ary Amborella) • Life cycle includes “double fertilization” Petal Sepal Figure 30.7 Receptacle Ovule Figure 30.7 The structure of a flower. Flow er = modified reproductive shoot More flower terminology with 4 circles (“whorls”) of modified leaves When brightly colored, aid in All petals together = attracting animal pollinators “corolla” “Male” parts, All stamens produce together = microspores, “androecium” which develop into “Female” parts, All carpels pollen grains produce together = megaspores & “pistil” or thus female “gynoecium” gametophytes, and ultimately How does this differ from the ovules and reproductive seeds structures of Ovary wall the other seed (pericarp) grows plants, the into fruit gymnosperms? Protects flower All sepals together before it opens = “calyx” Ovules found in cavity = “locule” 4 Trillium: a complete flower (has all 4 basic floral organs) Flower terminology: symmetry Grass flower: incomplete (lacks petals) Bisexual (perfect) flowers have both stamens and carpels, like this Lily Note: most grasses wind-pollinated Why might petals be unimportant for grasses? 5 Begonia, a monoecious species with unisexual (imperfect) flowers. Sagittaria: a dioecious species, with staminate flowers (left ), and carpellate (staminate flowers (left), carpellate flowers (right). flowers (right) growing on separate plants. In monoecious species, both sexes of flowers are found on a single plant. Why are the carpels and stamens similarly colored yellow? Grape hyacinth has flowers clustered in inflorescences. A solitary flower grows on a stalk called a peduncle Individual flowers in an inflorescence grow on pedicels The whole inflorescence is attached to a peduncle 6 Pyrethrum, a composite flower (a special kind of inflorescence). Notice the two types o f flowers, disc flowers (center) and ray flowers (at edge, each with a petal). Hypogynous Perigynous Epigynous Figure 30.12 Representatives of major angiosperm clades Figure 30.12 Monocots vs. Dicots • Flowering plants used to be divided into two groups: monocots and dicots • We now know that there are a number of different lineages that have the dicot morphology • Monocots are a monophyletic group 7 Monocots vs. non-monocots Figure 30.12 Monocots vs. Dicots (“dicots” = eudicots and other lineages) • Monocots (incl. lilies, orchids, yuccas, palms, grasses) usually have parallel veins in leaves, a single cotyledon, fibrous root systems, floral parts in multiples of three, and complexly arranged vascular bundles in stem • Dicots usually have net-like venation, two cotyledons, a taproot system, floral parts in multiples of four or five, and vascular bundles arranged in a ring in stem Review of flower terminology Pollination • 4 floral organs: sepal, petal, stamen, carpel • Avoiding self pollination • radial vs. bilateral symmetry • complete vs. incomplete flowers • Mechanisms of pollination: abiotic and biotic • bisexual (perfect) vs. unisexual (imperfect) flowers • Pollination syndromes • monoecious vs. dioecious plants • inflorescences and composite flowers • ovary position 8 Pollination: getting pollen to the Sexual vs. asexual reproduction stigma • Key potential advantage of sex: genetic variation in the • Required for sexual reproduction in plants: offspring, which could allow some to survive when pollination allows fertilization to take place. What faced with a rapidly changing environment (such as are the potential advantages and disadvantages of rapidly evolving diseases or a changing climate) sexual reproduction? • Potential disadvantages of sex: • A huge variety of adaptations have evolved in plants – Only half of the population (females) can produce offspring. In to ensure successful pollination, including biotic (via an asexual species, all individuals can reproduce, by cloning themselves animals) and abiotic (via wind or water) mechanisms – Sexual structures (e.g. flowers) are often costly – Pollination can sometimes be difficult, if animal pollinators or wind are not available, or if other members of the species are sparse – Sex can break up successful genotypes: offspring may be less- suited for the current environment than are the parents Ways to reproduce and avoid the Mechanisms for avoiding self- disadvantages of sexual reproduction pollination in sexual reproduction 1. Self-pollination or “selfing.” This is sexual 1. Being dioecious: male and female parts on reproduction (i.e. it involves meiosis and separate plants. fertilization), but offspring from selfing are genetically very similar to the parent 2. In monoecious plants, with separate male and female flowers on the same plant, 2. Asexual reproduction, or cloning. Only mitosis is these flowers mature at different times or involved, and offspring are genetically identical to are physically separated the parent (unless mutations occur during DNA 3. Dichogamy: stamens and carpels mature at replication). different times on the same (perfect) flower 4. Stamens and carpels are physically Many plant species reproduce only by self-pollination, and many also have the ability to reproduce asexually. separated in the same flower In what environments or situations would you expect these strategies to evolve? 9 Figure 38.5 Physical basis of self-incompatibility. Mechanisms for avoiding self- pollination in sexual reproduciton 1. Being dioecious: male and female parts on separate plants. 2. In monoecious plants, with separate male and female flowers on the same plant, these flowers mature at different times or are physically separated 3. Dichogamy: stamens and carpels mature at different times on the same flower 4. Stamens and carpels are physically separated in the same flower 5. Genetic self-incompatibility: pollen will not successfully fertilize if its self-sterility genes match those of the recipient plant Genetic basis of self-incompatibility. Pollen germination only occurs when the self-com patibility alleles of the pollen grain and the receiving plant do not match. Pollination ecology • 2 main modes of dispersal for pollen: abiotic (mostly wind but also water) and biotic (usually animals such as insects, birds, and bats) • These 2 strategies are thought to have different advantages in different environments 10
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