Instructions for printer-friendly copy.

x

x

x

x

x

x

x

x

x

x

    Anthophyta: The Flowering Plants

    Flowers are found only in the
    most derived plants, angiosperms.

      A flower is composed of whorls of

      • megasporophylls (carpels)
      • microsporophylls (anthers)
      • sterile leaves comprising the perianth

x

x

x

x

x

x

x

x

x

x

x

x

Alternation of Generations

Recall that in plants, the ploidy of any given individual is different from the ploidy of its parent or its offspring.

The diploid generation (sporophyte) and the haploid generation (gametophyte)
look completely different from one another.

This change in ploidy from parent to offspring is known as the Alternation of Generations.

sporophyte (2n) ---> gametophyte (n) ---> sporophyte (2n) ---> gametophyte (n) ---> sporophyte (2n) ---> etc.

x

x

x

x

x

x

x

x

x

x

    Flowering Plants: Reduced Gametophytes

    The flowering plants around us are sporophytes.
    Their offspring (which you can't see without a microscope) are gametophytes.
    The offspring of those gametophytes are more flowering sporophytes.

    The evolutionary progression of the alternation of generations saw

    • reduction of the gametophyte life cycle stage
    • increase in size and dominance of the sporophyte life cycle stage.

    This reaches it culmination in the Anthophyta.

x

x

x

x

x

x

x

x

x

x

    The Flower

    A flower is a shoot that terminates in leaves specialized for reproduction.
    Even the sterile leaves may assist in procuring sex.

    Sterile structures:

    • petal (single) and corolla (collective petals)
    • sepal (single) and calyx (collective sepals)
    • perianth (the petals and sepals together)

x

x

x

x

x

x

x

x

x

x

x

x

    Flowers: Simple and Compound

    A flower may be simple or compound.
    (compound = composite)

    • simple - one bloom on one peduncle
    • compound - multiple blooms on one peduncle.

    A cluster of flowers arranged on a single stem
    is called an inflorescence.

x

x

x

x

x

x

x

x

x

x

x

x


(click on pic for source)

    Phyllotaxy Still Applies

    Flowers are whorls of modified leaves.

    Therefore, there arrangement on the stalk has evolved
    from the arrangement of leaves on a stem.

    Flowers in an infloresence may be arranged as either

    • alternate
    • opposite

      ...along the peduncle.

x

x

x

x

x

x

x

x

x

x

x

x

x

x


(By Amada44; click on pic for source)

    Determinate and Indeterminate Inflorescences

    The apical meristem of an infloresence forms a terminal bud.

    In an indeterminate inflorescence (a.k.a. raceme)

    • the terminal bud grows continually, forming lateral flowers
    • a terminal flower is never formed
    • the infloresence exhibits (hypothetically) "infinite" growth
    • (or at least as long as the infloresence lasts)

    In a determinate inflorescence (a.k.a. cyme)

    • the terminal bud forms a terminal flower, which dies out.
    • lateral flowers sequentially grow from lateral buds and die out.
    • the infloresence has a finite number of blooms.

    And if you think it ends there, then...think again.

x

x

x

x

x

x

x

x

x

x

Trends in Flower Evolution
As insect pollinators drove the earliest evolutionary radiations of angiosperm flowers, four major trends appeared.

x

    1. Reduction of Metamerism

    Primitive condition
    • many copies of each flower part
    • indefinite number of each part

    Derived condition

    • reduced number of each flower part
    • specific number of each part
      • varies with species
      • multiples of 4-5 (dicots)
      • multiples of 3 (monocots)

x

x

x

x

x

x

x

x

x

x

x

x

    2. Reduced number of floral whorls

    Primitive condition
    • many whorls of perianth components
    • flower parts separate

    Derived condition

    • reduced number of perianth components
    • flower parts often fused

x

x

x

x

x

x

x

x

x

x

x

x

    3. Radial Symmetry --> Bilateral Symmetry

    Primitive condition
    • flower exhibits radial symmetry
    • flower is said to be actinomorphic
    • actin means "ray" in Greek

    Derived condition

    • flower exhibits bilateral symmetry
    • flower is said to be zygomorphic
    • zygo means "yoke" in Greek

x

x

x

x

x

x

x

x

x

x

x

x

    4. Shift of Ovary Position

    From more primitive condition to more serived condition:

    • hypogynous flower = superior ovary
      • perianth and stamens are attached below the ovary

    • perigynous flower = intermediate ovary
      • perianth and stamens are attached around the ovary,
        forming a cup

    • epigynous flower = inferior ovary
      • perianth and stamens are attached above the ovary,
        surrounding it

x

x

x

x

x

x

x

x

x

x

x

x


Complete flower: Hibiscus The hibiscus has all flower parts present.

    5. Loss of Flower Components

  • A complete flower has
    sepals, petals, stamens, and pistils.

  • An incomplete flower lacks
    one or more of the parts listed above.

    A complete flower exhibits the more primitive condition.

x


Incomplete flower: Bottle Brush The bottlebrush has flowers lacking petals.
(The stamens have evolved into the pollinator-attractors.)

x

x

x

x

x

x

x

x

x

x

x


Imperfect flower: female begonia

    6. Loss of Male or Female Sporophylls

  • A perfect flower has both stamens and pistils.

  • An imperfect flower has only stamens or only pistils.

    A perfect flower exhibits the more primitive condition.

    (By definition, an imperfect flower is also incomplete.)

x


Imperfect flower: male begonia

x

x

x

x



x

x

x

x


(source: Wikimedia Commons)

    Anthophyte Life Cycle

    In anthophytes, the reduction of the gametophyte generation reaches its culmination.

    • Male gametophytes lack antheridia.
    • Female gametophytes lack archegonia.

    They are stripped down and all business.

x

x

x

x

x

x

x

x

x

x

x

x

x

    Flower Microsporophyll: The Stamen

    Male structures:
    • stamen (microsporophyll)
      • anther (contains microsporangia)
      • filament (lower portion of microsporophyll)

    • pollen develops from a microspore
      • Pollen is NOT sperm, nor is it homologous to sperm.
      • Pollen is the mature male gametophyte.
      • Each haploid pollen produces two haploid sperm.

x

x

x

x

x

x

x

x

x

x

x

x


(click on pic for source)

    Flowering Plants:
    Male Gametophyte is Pollen

    Pollen is male, but it's not sperm.

    • Inside the flower's anther, diploid microsporocytes undergo meiosis.
    • This produces four haploid microspores.
    • Each microspore matures into a pollen grain.

      The pollen is the mature male gametophyte.
      It will produce two sperm.

x

x

x

x

x

x

x

x

x

x

    Flower Megasporophyll: The Carpel

    Female structures:
    • carpel (megasporophyll)
      • stigma (pollen landing pad)
      • style (filamentous tube)
      • ovary (ovulary) (contains megasporangia)

    A flower may have one or more carpels.
    The entire female structure comprises a pistil,
    which may be composed of one to many carpels.

x

x

x

x

x

x

x

x

x

x

x

x

x

    Flowering Plants:
    Female Gametophyte is Hidden in the Ovule

    Inside the ovary...
    • diploid megasporocytes are nestled in ovules (2n) made of maternal
      • integuments (will become the seed coat)
      • nucellus (sporophyte tissue)

    • Each megasporocyte produces four haploid nuclei via meiosis.
    • Each haploid nucleus divides again.
    • The final product will be eight haploid nuclei in a mass of cytoplasm.

    The eight nucleate mass surrounded by the sporophyte's integuments comprise the ovule.

    An ovary (ovulary?) may contain one to hundreds of ovules,
    depending on species.

x

x

x

x

x

x

x

x

x

x

x


(By Lokal_Profil; click on pic for source)

    The Female Gametophyte

    The eight nuclei migrate to specific positions:
    • ovum (adjacent to the micropyle)
    • synergids (flanking the ovum)
    • polar nuclei (center)
    • antipodals (adjacent to the chalaza)

    This eight-nucleate "embryo sac" is the female gametophyte!
    She is enclosed in maternal integuments that will become the seed coat.

    The embryo sac is the daughter of the flowering, diploid sporophyte.

x

x

x

x

x

x

x

x

x

x

x

    Pollination: Driver of Flower Evolution

    Flowers of a given plant family
    • have specific characteristics
    • tend not to vary within a family

    The earliest flowers most likely

    • did not have distinct sepals and petals
    • were not showy

    Selection exerted by animal pollinators changed that in many species.

x

x

x

x

x

x

x

x

x

x

x

x

x

    Showing Off for Sex

    In response to preferences of pollinating insects and vertebrates,
    different flowers evolved different colors, shapes, and other attractants
    to draw in animals to help with their fertilization.

    • parts of the perianth became showy
      and attractive to pollinators

    • either sepals or stamens evolved into petals
      • sepals - same number of vascular strands as the leaves (water lilies)
      • petals (and most stamens) - usually only one vascular strand (almost everyone else)

x

x

x

x

x

x

x

x

x

x

    Pollinators and Pollination Syndromes

    A pollination syndrome is a set of traits exhibited by flowers
    that are pollinated by a specific factor such as...

    • wind or water (abiotic pollinators )
    • animals (biotic pollinators )

x

x

x

x

x

x

x

x

x

x

    Pollination in Flowering Plants

    All seed plants undergo pollination,
    the arrival of pollen at the female structure.

    Pollen may be borne by

    • wind
    • water
    • animal pollinators

    Pollen morphology is species specific.
    Stigma and pollen are as lock to key.

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

    Pollination and Fertilization

    Pollination is the arrival of pollen on the stigma.
    Fertilization is the fusion of sperm and ovum.
    Fertilization may occur days or months after pollination.

    Remember that each pollen contains two genetically identical sperm.
    Both sperm participate in fertilization.
    This double fertilization is unique to flowering plants:

    • One sperm joins with the ovum to become the zygote.
    • The other sperm joins with both polar nuclei to become
      triploid endosperm that will feed the growing embryo.

x

x

x

x

x

x

x

x

x

x

x

x

    Double Fertilization

    When the pollen tube reaches the micropyle,
    it releases its two sperm.

    • One sperm fuses with the ovum to produce the zygote (2n)
      • This develops into the plant embryo.
      • Ultimately, it will be the new sporophyte.

    • One sperm fuses with the polar nuclei to produce the endosperm (3n)
      • This will proliferate to form 3n nutritive tissue for the embryo.
      • It's the embryo's edible sibling!

x

x

x

x

x

x

x

x

x

x



(click on pic for source)

    Pollination is not Fertilization

    Pollination is the delivery of pollen to the stigma of the flower.
    • Pollen lands on the stigma.
    • Tube cells give rise to a pollen tube.
    • Generative cell divides into two sperm.
    • Pollen tube grows through the style into the ovary.

    Fertilization is the fusion of sperm and ovum nuclei.
    • Two sperm travel down the pollen tube to the ovule.
      • one sperm + ovum --> zygote (2n).
      • one sperm + polar nuclei --> endosperm (3n).
      • This is known as double fertilization.

    Upon fertilization, the ovule becomes a seed.

    The walls of the ovary will ripen into a fruit.

x

x

x

x



x

x

x

x


(click on pic for source)

    x

    x

    Fruit

    A fruit is
    • the mature ovary of the flower
    • often composed of tissues other than the ovary
    • the container of the seeds

    Each seed carries a genetically unique offspring of the plant bearing the fruit.

x

x

x

x

x

x

x

x

x

x

Before There Is Fruit, There Must Be Sex.

Plant sex is...complicated.

Individuals of one generation have a different ploidy than the previous or subsequent generation.

The diploid generation (sporophyte) and the haploid generation (gametophyte) look completely different from one another.

This change in ploidy from parent to offspring is known as the Alternation of Generations.

sporophyte (2n) ---> gametophyte (n) ---> sporophyte (2n) ---> gametophyte (n) ---> sporophyte (2n) ---> etc.

  • The flowering plants around us are sporophytes.
  • Their offspring (which you usually don't see) are gametophytes
  • x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x


    (click on pic for source)

      Plants: A Complex Life Cycle

      A sporophyte is diploid.
      • Meiosis occurs in specialized compartments called sporangia.
      • A mature sporophyte produces haploid spores via meiosis.
      • A spore grows into a haploid gametophyte via mitosis.


      A gametophyte is haploid.
      • Mitosis occurs in sex organs called a gametangia:
        • antheridium (male) produces sperm.
        • archegonium (female) produces ova.
      • Fusion of ovum and sperm produces a diploid zygote.
      • The zygote grows into a diploid sporophyte.

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

      Fruit: More Complex Than You'd Think

      A fruit has several layers derived from the parent sporophyte tissues...
      • pericarp
        • exocarp (outer layer)
        • mesocarp (middle layer)
        • endocarp (inner layer)
      • seed coat (inside endocarp)

      The offspring in the seed include...

      • embryo (ovum + sperm)
      • endosperm (polar nuclei + sperm)

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

      Simple, Aggregate, and Multiple Fruit

      A simple fruit is formed from a single flower with a single pistil.
      • tomato
      • blueberry
      • peanut

      • peach
      • banana

      An aggregate fruit is formed from a single flower with many pistils borne on the same receptacle. One peduncle per fruit.

      • strawberry
      • blackberry
      • raspberry

      • raspberry
      • boysenberry

      A multiple fruit is the fusion of a cluster of individual flowers in a
      single inflorescence. Each "fruitlet" has its own receptacle and its own pedicel.

      • pineapple
      • kiwi fruit

      • mulberry
      • fig

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x


    (click on pic for source)

      Accessory Fruit

      An accessory fruit is one in which the fleshy pericarp is composed of floral tissue in addition to the walls of the ovaries.

      The pistil of an apple blossom (an epigynous flower) develops into the papery apple "core" and a bit of adjacent tissue. The fleshy, edible part of the fruit is derived from the receptacle, which has grown up to surround the pistil.

      The "seeds" on the outside of a strawberry are the actual fruits. The fleshy, sugar-filled "fruit" designed to attract seed dispersers such as birds, monkeys or yourself is actually the receptacle that has evolved the function of attracting animal seed dispersers.

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

      Categorizing Fruit

      At seed maturity, fruit can be

      • fleshy - mesocarp moist and pulpy at seed maturity
        • berry
        • drupe
        • pome

      • dry - mesocarp dry at seed maturity

        • dehiscent - splits open to release seeds
          • follicle
          • legume
          • capsule

        • indehiscent - does not split to release seeds

          • achene
          • nut
          • grain

        (There are several other types of dry fruit,
        but you can learn those in BIL 226.)

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

      Fleshy Fruit: The Berry

    • true berry
      • fleshy endocarp, mesocarp and exocarp
      • one to many seeds

    • pepo
      • thick, rigid pericarp
      • numerous seeds separated from pericarp

    • hesperidium
      • aromatic, leathery exocarp
      • mesocarp and endocarp compartmentalized
        into sections (each representing a carpel)
      • each carpel contains one to several seeds
      • many parthenogenetic varieties are popular in the produce section

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

      Fleshy Fruit: The Drupe

      A drupe
      • has a single seed enclosed in a hard endocarp
      • endocarp may be called a "stone" or "pit."
      • exocarp soft and thin
      • mesocarp soft and fleshy

          These are drupes!
          • peach
          • apricot
          • plum
          • mango
          • olive

          These are drupes,
          not nuts!
          • coconut
          • walnut
          • almond
          • pecan
          These are clusters of drupelets, not berries!
          • raspberries
          • blackberries

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x


    (click on pic for source)


    (click on pic for source)

      They're Drupes, Not Nuts

      Many "nuts" sold commercially
      are not true nuts at all.

      These images show:

      • coconut (top left)
      • walnuts (lower left)
      • almonds (top right)
      • pecans (lower right)

      ...in their complete fruit state.

      The "nut" is actually endocarp ("shell") and seed.

      So go get your money back.


    (click on pic for source)


    (click on pic for source)

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x


    (click on pic for source)

      They're Drupelets, Not Berries.

      And those raspberries, blackberries, and boysenberries?

      They're not berries, either.

      Each little fleshy "bubble" on one of these "berries"
      is actually a miniature drupe, or drupelet.

      The aggregate fruit was formed from a single flower
      bearing multiple pistils on a single receptacle.

      The receptacle may be removed during harvest and processing,
      leaving the hollow, aggregate fruit.

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

      Fleshy Fruit: The Pome

      A pome
      • develops from an epigynous flower
      • ovary becomes a papery/leathery endocarp
      • pistil consists of five carpels
      • endocarp is star-shaped in cross section
      • epigynous receptacle becomes exocarp and mesocarp
      • thin, soft exocarp
      • fleshy mesocarp

      A pome is an accessory fruit because
      it is formed from flower tissue (receptacle)
      in addition to the ovary walls.

      Most pome-bearing plants are in the Rosaceae,
      the Rose Family.
      (Notice the apple's faintly rose-like scent.)

      Examples: apple, pear, loquat, quince

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    Dry, Dehiscent Fruits

    A dry fruit has a dry, hard pericarp at seed maturity.
    A dehiscent fruit splits at maturity to release seeds.
    (To dehisce means to split open.)

    x


    source: Wikimedia Commons

      Follicle

      A follicle consists of a single carpel that
      splits along one seam to release seeds.

      Examples: milkweed, Magnolia


    (click on pic for source)

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

      Capsule

      The most common type of fruit, a capsule
      consists of multiple carpels that
      split along one seam per carpel to release seeds.

      Produced by many different angiosperm species.

      Examples: Many!
      Mahogany, cotton, eucalyptus, poppy, star anise
      (A Brazil "nut" is actually a seed from a giant
      "monkey pot" capsule.)


    (By Alex Popovkin, Bahia, Brazil, Wikimedia Commons)

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x


    By Bill Ebbesen, Wikimedia Commons

      Legume

      Unique to the Pea Family (Fabaceae), a legume
      consists of one carpel that splits along two seams
      to release its seeds.

      Though we use many as food,
      most legumes are toxic.

      (Coumarin , a powerful anticoagulant found in clover
      and other legumes, is used to make warfarin .)

      Examples: green beans, peanuts, sweet peas, many tropical trees (e.g. Royal Poinciana)


    By Texnik, Wikimedia Commons

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    Dry, Indehiscent Fruits

    A dry fruit has a dry, hard pericarp at seed maturity.
    An indehiscent fruit does NOT split at maturity to release seeds.

    x


    (click on pic for source)

      Achene

      An achene has a thin, dry pericarp
      attached only at its base to a single seed inside.

      Many different species, from roses to quinoa, make achenes,
      including all members of the daisy family (Asteraceae).

      Examples: sunflower "seeds", strawberry "seeds",
      dandelion, quinoa, buckwheat

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x


    (click on pic for source)

      Nut

      A nut is similar to an achene,
      but with a thicker, harder pericarp.

      A nut develops in a little "cup" formed by fused bracts
      at the base of the flower.

      Examples: acorn, hazelnut, macadamia nut, chestnut

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x


    (source: Getty Images)


    (click on pic for source)

      Grain

      A grain is a single-seeded fruit
      whose pericarp is completely fused to the seed.

      Because the pericarp and seed are so tightly united,
      whole grains are a good source of dietary fiber.

      The grain is unique to the Grass Family (Poaceae).

      Seventy five percent of the world's human population
      relies upon rice as a major staple food source.

      Corn farming is a multi-$billion/year industry in the U.S.

      Products range from the cornstarch coating
      on the pages of your textbook to the high-fructose corn syrup
      in your soda to the ethanol in your car's gas tank.

      Examples: rice, wheat, corn, barley, rye, bamboo, sugar cane


    (click on pic for source)


    (click on pic for source)