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
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4 - 6 months between
pollination &
fertilization
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
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Evolution of Seed Plants
Gymnosperms
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 Plants
Gymnosperms
• 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 Plants
Gymnosperms
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: Ginkgophyta
Reproduction: 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: Ginkgophyta
Reproduction: 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: Ginkgophyta
Reproduction: Development
•
seed
Div: Ginkgophyta
Reproduction: 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”
• 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.
• Evolved during the
Carboniferous Period 325 mya
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
• Seed or Ovulate Cone
• Pollen or Staminate 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