Download Seedless Vascular Plants

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Seedless Vascular Plants
Ferns and Their Relatives
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Introduction
 Once
plants like bryophytes became
adapted to living on the land,
evolution continued to select for
plants that had traits favorable to this
strange, dry territory.
 Today’s
descendants of these early
plants reveal the traits that made them
successful.
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Successful Land Traits
 Better
control of internal water
concentration.
 Plants
developed thicker cuticles, providing
better waterproofing.
 Plants also developed stomata that could open
and close became the norm, rather than pores
like those in bryophytes that stay open all the
time.
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Successful Land Traits
 Development
of roots to increase
water and mineral uptake from the soil.
 Scientists
think roots evolved in ancient
vascular plants from stems that grew along or
just under the surface of the soil.
 Once these surface branches started growing
under the surface of the soil, they were
exposed to different conditions than the
branches above the ground.
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Successful Land Traits
 Plants
whose underground branches
were able to absorb water had an advantage
over other plants, leading to the evolution of a
more root-like structure over time.
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Successful Land Traits
 Internal
vascular tissue for conducting
water and sugar throughout the plant
body.
 In
particular, the development of waterconducting tracheids helped change the way
plants grow.
 Because of their strong, lignified cell walls,
tracheids provide greater structure and
support to plants, enabling plants to grow
more erect.
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Successful Land Traits
 A
more erect, branched pattern of
growth.
 Branching
let the early land plants produce
multiple sporangia per plant, increasing their
chances of reproductive success.
 Once plants started producing leaves,
branching allowed plants to spread their
leaves out so that they didn’t shade each
other, maximizing the capture of sunlight for
photosynthesis.
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Successful Land Traits
 The
evolution of leaves, allowing
better capture of light.
 Small
simple leaves called microphylls,
evolved in a group of plants called lycophytes.
 Microphylls are simple leaves with a single
unbranched vein of vascular tissue.
 In addition, larger, more complex leaves called
megaphylls developed in almost all other
vascular plants.
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Successful Land Traits
 Megaphylls
have branching veins.
 Scientists think megaphylls evolved when leaf
tissue grew around small, flat clusters of
branches, joining them together in a leaf-like
structure.
 Over time, the branches became the
branching veins within the leaf.
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Successful Land Traits
 The
combination of these new traits
gave plants much better control over
their internal water content, increased
their reproduction, and improved
their ability to effectively harvest light
for photosynthesis.
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Successful Land Traits
 Another
important characteristic of
plants that first appears in the seedless
vascular plants is heterospory.
Heterosporous plants produce two
different types of spores.
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 Megaspores
are larger and grow into female
gametophytes.
 Microspores are smaller and grow into male
gametophytes.
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Successful Land Traits
 Within
the plant kingdom, heterospory
evolved may times, so scientists think it must
have given plants a real advantage.
 Many
plant groups today, including the very
successful flowering plants, are
heterosporous.
+ Devonian Periods
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Successful Land Traits
 After
these evolutionary innovations
occurred, groups of land plants expanded
and evolved into many different species,
creating a burst in plant diversity between
417 and 354 million years ago (the Devonian
Period) that eventually led to the
development of the first forests between 354
and 290 million years ago (the
Carboniferous period).
+ Carboniferous Forest
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Successful Land Traits
 Over
these time periods, the relationship
between the gametophyte and sporophyte
generation changed.
 Sporophytes
became the more dominant
plant generation.
 Gametophytes got progressively smaller and
more protected by the sporophyte.
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Successful Land Traits
 Botanists
think that the reason sporophytes
became dominant is that all the adaptations
that allow plants to survive in dry
environments evolved in sporophytes.
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Successful Land Traits
 All
seedless vascular plants have several
characteristics in common:
 The
sporophyte is the dominant phase of the life
cycle, but the gametophyte is independent and
photosynthetic.
 The sporophyte makes and disperses spores from
sporangia.
 The gametophyte makes gametes in gametangia.
 They require water for sexual reproduction so the
sperm can swim to the egg.
 The sporophyte has vascular tissue, a cuticle, and
stomates.
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Phylum Psilotophyta: the whisk ferns
 Whisk
ferns loosely resemble small, green
whisk brooms.
 Whisk
fern structure:
 Evenly
 No
forked stems which are photosynthetic
roots or leaves
 Enations
(tiny, green leaf-like outgrowths on the
stems) present
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Step 6
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Phylum Psilotophyta:
the whisk ferns
Step 7
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Step 1
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Phylum Psilotophyta: the whisk ferns
 Reproduction:
 1. Small
sporangia are borne on short stubby
branches.
 2. Meiosis
occurs in sporangia producing
meiospores.
 3. Meiospores
germinate slowly on soil or bark of
tree ferns.
 4. Gametophytes
found beneath the soil are very
small (2mm x 6mm).
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Phylum Psilotophyta: the whisk ferns
 5. Archegonia
and antheridia are produced on this
colorless gametophyte.
 6. Fertilization
occurs in the archegonium.
 7. Sporophyte
develops from the zygote.