Evolution of Cycads, Gymnosperms and Ferns

Div: Progymnospermophyta

• 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: Pteridospermophyta “Seed Ferns”

• 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: Cycadophyta “Cycads”

• 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”

• 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

Div: Ginkgophyta

• 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: GinkgophytaReproduction: Dioecious

• 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: Fertilization the 2nd Year

• generative cell --> 2 flagellated sperms (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: Development

• seed

•

Div: GinkgophytaReproduction: Development

• Outer fleshy layer of the integument emits foul order!

• However, inner part of the seed is edible!

•

•

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

• 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

• Pollen or Staminate Cone

• Seed or Ovulate Cone

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