Evolution of cycads gymnosperms and ferns
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Evolution of Cycads, Gymnosperms and Ferns . Gymnosperm anatomy - secondary xylem tracheids , circular bordered pits - and fern-like fronds & reproductive dispersal by spores . (no seeds) Arose in Upper Devonian 350 mya --> Pennsylvanian 290 mya All extinct

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Evolution of Cycads, Gymnosperms and Ferns

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Evolution of Cycads, Gymnosperms and Ferns


Gymnosperm anatomy - secondary xylem tracheids, circular bordered pits - and fern-like fronds & reproductive dispersal by spores. (no seeds)

Arose in Upper Devonian 350 mya --> Pennsylvanian 290 mya

All extinct

Probably the immediate ancestor of all seed plants.

Archaeopteris

Div: Progymnospermophyta


Gymnosperm anatomy and gymnosperm seed type with fern-like fronds. (seeds on fronds)

Arose during Carboniferous Period 345 mya --> Permian 250 mya.

All extinct

Probably the immediate ancestor of the cycads.

Div: Pteridospermophyta “Seed Ferns”


Ovules (megasporangium with embryo after fertilization) develop into “seeds” covered with two cells layers from integument or seed coat.

Naked Seed, “Gymnosperm”

Monoecious

Div: Pteridospermophyta “Seed Ferns”


Resemble “palm trees”.

Cycad foliage does not bear ovules or seeds - these are in special seed cones (strobili); pollen (with sperms) produced in pollen cones.

Arose during Permian Period 280 mya --> extant

A dominant form of vegetation during the Jurassic and Triassic Periods --> 135 mya.

Div: Cycadophyta “Cycads”


Div: Cycadophyta “Cycads”

  • All are dioecious: Micro and Megasporangia (strobili) on separate plants.

  • Cycas


Div: Cycadophyta “Cycads”

  • Reproductive cycle in cycads wind pollination; pollen droplet

  • 4 - 6 months between

  • pollination &

  • fertilization

  • interval between pollination and fertilization: 4 - 6 months.


Div: Cycadophyta “Cycads”

  • Two motile sperms produced by each pollen tube --> archegonial chamber.

  • Cycads & Ginkgos are

  • only seed plants with

  • motile sperm


Div: Cycadophyta “Cycads”

  • No fixed period of dormancy in cycads.


Evolution of Seed Plants

  • Derived Trait


Evolution of Seed PlantsGymnosperms

  • Pollen - Encased male microgametophyte (n) that produces

  • sperms(n).

  • (Frees plant from the need for water in the pollination

  • process.)

  • prothallus cell(s), tube cell(s), generative cell

  • ---> sperms

  • Ovule - The female megagametophyte (n) with eggs (n) surrounded

  • by the old megasporangium (2n) with two layers from the

  • old sporophyte (2n) that will form the integument (2n).

  • (Frees plant from the need for water in fertilization.)

  • Cones - An axis bearing a tight cluster of scales or leaves for

  • reproduction. Scales either bear microsporangia or

  • meagasporangia in separate cones. (Pollen & Seed Cones)

  • Seed - ?


Evolution of Seed PlantsGymnosperms

  • Seed - The matured ovule with an embryo in a resting state.

    • Integument - (2n) May be fleshy

    • Female Gametophyte - (n) nuritive; includes nucellus

    • Embryo - (2n) forms from zygote after fertilization.


Evolution of Seed PlantsGymnosperms


Div: Ginkgophyta“Ginkgos,Maidenhair Trees, Yin hing (silver apricot)”

  • Arose during the Permian 250 mya.

  • Richly branched woody plant with simple leaves.

  • Ginkgo biloba living fossil


1. Large stems; small simple leaves; deciduous.

2. Dioecious (female more shrubby)

Div: Ginkgophyta


1. Large stems; small simple leaves; deciduous.

2. Dioecious (female more shrubby)

3. Has bud scales; dimorphism in branches. (long and spur shoots).

4. Stomates on abaxial (bottom) of leaf; two vascular bundles and 2 leaf traces per leaf.

Div: Ginkgophyta


1. Large stems; small simple leaves; deciduous.

2. Dioecious (female more shrubby)

3. Has bud scales; dimorphism in branches. (long and spur shoots).

4. Stomates on abaxial (bottom) of leaf; two vascular bundles and 2 leaf traces per leaf.

5. Initiation of cambium after primary growth; growth rings.

6. Cork cambium or phellogen develops in outer cortex --> phellem (cork cells, bark)

Div: Ginkgophyta


Microsporangia (2n) - strobili

1 yr. --> microsporocyte (2n) --> meiosis --> microspores (n) Spring --> pollen (male gametophyte)

Pollination (pollen droplet mucilaginous) -->

Megasporangia - ovules

1 yr. Development of megasporocyte (2n) --> meiosis --> megaspore (n) --> female gametophyte ( with egg - n) as pollen tube grows - after 5 mos.

(Aug-Oct) fertilization - development of seed - 2nd yr.

Div: GinkgophytaReproduction: Dioecious


generative cell --> 2 flagellatedsperms (just prior to fertilization) --> swim to end of pollen tube

egg from archegonium swells and forces apart neck cells --> exposed to pollen tube and sperm for fertilization.

Micropyle

Div: GinkgophytaReproduction: Fertilization the 2nd Year


seed

Div: GinkgophytaReproduction: Development


Outer fleshy layer of the integument emits foul order!

However, inner part of the seed is edible!

Div: GinkgophytaReproduction: Development


Evolved during the Carboniferous Period 325 mya

Div: Coniferophyta“Pines”, “Spruces” and “Firs”


Div: Coniferophyta“Pines, Spruces and Firs”


Div: Coniferophyta“Pines, Spruces and Firs”


Evolved during the Carboniferous Period 325 mya

1. Leaves simple; often needle-like or scale-like.

2. Xylem compact, composed mostly of tracheids (seasonal growth - rings).

3. Pith and cortex restricted - xylem composes most of the stem.

Div: Coniferophyta“Pines”, “Spruces” and “Firs”


1. Leaves simple; often needle-like or scale-like.

2. Xylem compact, composed mostly of tracheids (seasonal growth - rings).

3. Pith and cortex restricted - xylem composes most of the stem.

Div: Coniferophyta“Pines”, “Spruces” and “Firs”


1. Leaves simple; often needle-like or scale-like.

2. Xylem compact, composed mostly of tracheids (seasonal growth - rings).

3. Pith and cortex restricted - xylem composes most of the stem.

4. Stem may be differentiated into long and spur shoots.

Div: Coniferophyta“Pines”, “Spruces” and “Firs”


Div: Coniferophyta“Pines”, “Spruces” and “Firs”


1. Leaves simple; often needle-like or scale-like.

2. Xylem compact, composed mostly of tracheids (seasonal growth - rings).

3. Pith and cortex restricted - xylem composes most of the stem.

4. Stem may be differentiated into long and spur shoots.

5. Leaf traces one or few per leaf.

6. Typically evergreen; loose leaves gradually.

7. Protostelic taproot.

Div: Coniferophyta“Pines”, “Spruces” and “Firs”


Div: Coniferophyta“Pines”, “Spruces” and “Firs”


Pollen or Staminate Cone

Seed or Ovulate Cone

Div: Coniferophyta


Div: Coniferophyta

  • Pine Pollen


Div: Coniferophyta

  • Ovulate Pine Cones:


Div: Coniferophyta

  • Mature Pine Ovule with Two Archegonia:


Div: Coniferophyta

  • Ovules at Fertilization and with Embryo:


Div: Coniferophyta

  • Pine Seedling:


Div: Coniferophyta


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