Plant Diversity

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Plant Diversity

• Plants life emerged from charophycean alga
• Multicellular, eukaryotic, photosynthetic
  autotrophs, cellulose cell walls
• Chlorophylls a, b and beta carotene present in
  plastids
• Rosette cellulose synthesizing complexes
• Peroxisome enzymes to minimizes loss of organic
  product due to photorespiration
• Similar sperm structure
• Cell division includes phragmoplast for cell wall
  synthesis

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Emerging from the water . . . had its ups

• Plenty of space was available
• Plenty of carbon dioxide
• Rich soil was abundant in nutrients
• Sunlight was not filtered by water

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. . . and its downs

• Lack of buoyant support
• Nutrients were no longer delivered by water
  current
• Water shortage and loss
• Reproductive cells relied on water for transport

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Adaptations were required for . . .

• Prevention of water loss
• Transport of water and nutrients
• Structural support of the plant
• Transport of reproductive cells without the use
  of water

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Bryophytes

• Non vascular plants
• Hepatophyta liverworts
• Anthocerophyta hornworts
• Bryophyta mosses
• Earliest plants
• Not fully adapted for land

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Restrictions of bryophytes

• Must remain small and thin for absorption to be
  effective
• Have to remain close to the ground
• Survives mainly in moist areas
• Relies on water for sperm transport

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Traits of Bryophytes

• Dominant gametophyte (haploid state)
• Delayed meiosis produces emergence of alternation
  of generation
• Gametangia form protective layers around the
  gametes
• Embryo form within the female gametangium
• Sporophyte (diploid state) dependent on
  gametophyte

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Hepatophyta

• Gametophytes can appear as thalloid or leafy
• Rhizoids anchor thallus or leaflike blades to
  ground
• Lack stomata - but some have similar pores
• Sexual reproduction involves production of
  archegonia and antheridia on gametophyte

Liverworts can reproduce asexually through gemmae
or thallus branching.
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Marchantia

• Archegoniophores form archegonia beneath their
  umbrella structures and antheridiophore house
  antheridia on top for sperm production.
• Separate male and female gametophytes can be
  noticed in this picture. The one on the left has
  female structures while the one on the right has
  male structures.

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Hornwort

• Thalloid gametophytes
• Single large chloroplast in each cell
• Archegonia and antheridia embedded in thallus
• Sporophyte is horn shaped and form sporangium
  where meiosis occurs
• Sporophyte will continue to grow from base as
  long as gametophyte is alive

The sporangium at the tips of these sporophytes
will split open releasing spores.
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Bryophyta

• Many mosses are dioecious, some are monoecious
• Sporophytes are dependent on the gametophyte
• Hydroids, leptoids, and rhizoids show similarity
  to the xylem, phloem, and roots of other plants
• Leaf like blades are undifferentiated

Sphagnum plants contain many large dead cells
that are able to absorb water. This makes peat
moss a great soil conditioner.
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Pteridophytes Tracheophytes

• Developed true leaves, true stems, and true roots
  
• Lignified vascular tissue used for transport
• Xylem made of tracheids are present for the
  transport of water up
• Phloem made of sieve cells and companion cells
  are used for transport of nutrients
• Made of two divisions Lycophyta and Pterophyta
  (well talk about what happened to Psilophyta and
  Sphenophyta)

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Psilophyta

• Otherwise known as whisk ferns
• Shows dichotomous branching
• Lacks true leaves and roots, but has a vascular
  system.
• Scale like protrusions from the stem may be a
  precursor to leaf development

Along with the development of the vascular
system, we see a shift to a more dominant
sporophyte. Sporophyte and gametophyte can exist
independently of each other.
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Phylum Lycophyta

• Ancient lycophytes were 40m giants which died out
  as the climate cooled
• Modern lycophytes are epiphytes club mosses
• Roots extend down from horizontal stems
• Characterized as upright stems with many
  microphylls, and strobili for reproduction

Although many lycophytes are epiphytes, using
trees as a substrate to grow on, these are
growing on the forest floor.
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Microphyll development

• Microphylls are small leaves with only a single
  unbranched vein. They probably evolved from
  flaps of tissue protruding from the surface of
  stems, which vascular tissue then extended into.

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Sphenophyta

• Equisetum horsetails are typical of the phylum
  sphenophyta
• They have horizontal rhizomes which sprout
  upright green stems with small leaves.
• They produce cones composed of sporophylls

The cones seen here are very similar to the
strobili of the lycophytes. They are both
derived from leaf-like structures bearing
sporangia.
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Phylum Pterophyta

• Commonly known as ferns
• Horizontal rhizomes
• Have large leaves with branched vascular systems
• Sporophyte megaphylls form sporangia clusters
  called sori
• Heart shaped prothallus anchored by rhizoids
  forms the archegonium and the antheridium

The megaphylls of plants contain branched
vascular strands in order to deliver the
nutrients to all cells efficiently. (Its that
surface area thing again . . . )
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This shows the cycle of a homosporous pterophyte.
However, some ferns and club mosses have become
heterosporous, where two types of spores are
created through meiosis. Megaspores usually
develop into female gametophytes, and microspores
into male gametophytes.
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A few more things to note . . .

• Psilophyta and Sphenophyta are now grouped into
  one phylum with Pterophyta
• Molecular studies show they are too closely
  related to be put in separate groups.
• Development of a vascular system gave these
  plants an advantage by allowing upward growth
• Able to receive more sunlight and shadow the
  light from the competition.
• One problem of inhabiting land that they did not
  overcome was their reliance on water for
  reproduction.

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Gymnosperms

• Formation of pollen was critical for breaking the
  dependency on water for reproduction
• Seeds with the sporophyte embryo packaged along
  with a food supply in a protective coat allowed
  for more efficient dispersal of offspring
• We see a stronger shift towards a dominant
  sporophyte, where the gametophyte is further
  reduced (microscopic) and becomes dependent on
  its larger counterpart

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• Formation of pollen and seeds developed with the
  shift towards heterospory
• Megasporangium form megaspores which develop into
  the female gametophyte in the form of a seven
  celled ovule
• Microsporangium form microspores which develop
  into the male gametophyte as two celled pollen
  grains covered with sporopollenin
• Once fertilization occurs a seed forms with the
  embryo inside

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Phylum Ginkgophyta

• Has Ginkgo biloba as its only surviving species
• Dioecious plants where male trees give off pollen
  while female trees produce the fleshy seed that
  gives off foul odors.
• Important medicinal plant is rumored to increase
  memory by improving blood flow to the brain

Would this Gingko plant be a male or female
plant? Perhaps neither - how can you tell?
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Phylum Cycadophyta

• Resembles a palm tree
• Reproduction is similar to that of a pine,
  however a cycad is dioecious
• Motile sperm are multiflagellated and residual
  from primitive ancestors

The seed cone above appears in the form of a
female strobilus. These structures are large
considering most cycads are short plants.
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Phylum Gnetophyta

• Welwitschia - found in southwestern Africa
• - has straplike leaves extending
  from a long underground taproot
• - - - - - - - - - - - - - - - - - - - - - - - - -
  - - - - - - - - -
• Gnetum - tropical trees or vines
• - broad leaves resemble those of flowering
  plants
• - - - - - - - - - - - - - - - - - - - - - - - - -
  - - - - - - - - -
• Ephedra - American desert shrubs
• - stimulates the heart, raising blood
  pressure

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Gnetophyta make strides . . .

• More advanced than the other gymnosperms
• Vessel elements are added to the xylem
• Cone clusters resemble flowers of angiosperms
• Double fertilization resembles the process that
  angiosperms undergo

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Phylum Coniferophyta

• The most abundant of seed plants
• Includes pines, firs, spruces, cedars, cypresses,
  redwoods, junipers, etc.
• Most are evergreen
• Needle-shaped leaves are adaptive for dry
  conditions
• Thick cuticle and placement of stomates in pits
  prevent dessication.

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• Coniferous trees are among the largest and oldest
  organisms on Earth
• The pine trees are the sporophytes of these
  plants
• Conifers, like all seed plants are heterosporous
• Each tree usually has both types of cones
• This makes the trees monoecious

The Lone Cypress stands by itself in Monterey.
As a stop on the 17 Mile Drive, it is one of the
most photographed trees.
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Reproductive Cycle of Conifers
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Angiosperms Developed Flowers

• All angiosperms have been placed into the single
  phylum of Anthophyta
• The two main classes that fall into this phylum
  are Monocotyledonae and Dicotyledonae
• Recent studies have shown monocots to be
  monophyletic, but dicots do not form a
  monophyletic group

The Amborella is the only survivor of a branch at
the very base of the angiosperm lineage.
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Monocots, Dicots and More. . .

• Monocots usually have parallel venation, flower
  parts in arrangements of threes, scattered
  vascular bundles, one cotyledon, no secondary
  growth and a fibrous root system
• Dicots have netted venation, flower parts in
  multiples of fours or fives, a circular ring of
  vascular bundles, two cotyledons, secondary
  growth, and a tap root system

Waterlilies and the Star Anise diverged earlier
than the monocots and dicots.
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Look at the pretty flower . . . .

• Flowers are made of 4 whorls of sepal, petals,
  stamen, and carpels
• Complete flowers have all four whorls
• A flower with both stamens (male) and carpels
  (female) is perfect
• The megaspore develops into the embryo sac
  (female gametophyte) which is protected within
  the ovary

Flowers allowed for more efficient dispersal of
pollen increasing cross fertilization.
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Evolution of the Ovary . . . .
The enclosure of the seed within the ovary is a
feature of angiosperms that evolved from a
sporophyll (seed-bearing leaf) that rolled into a
tube. Some flowers have single carpels, some
have several separate carpels, and some have
fused carpels.
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Peas are fruits . . . .
A fruit is a mature ovary. As the seeds develop,
the wall thickens to form the pericarp of the
fruit which protects and aids in dispersal.
. . . not vegetables.
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Adaptations That Help With Dispersal

• Tasty fruits allow dispersal after passing
  throught the digestive tracts of animals
• Propeller like structures allow wind to carry the
  seeds
• Burrs cling to the fur of animals in order to
  disperse
• First, pollination and fertilization must occur
  in order for these seeds and fruits to develop

Some seeds are required to pass through the
digestive tract of animals before they can
germinate.
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Birds do it . . .
Bees do it . . .

• Flowers increase chances of cross pollination by
  having certain animals distributing their pollen.
• Coevolution between pollinator and plant can be
  seen in the beak of the hummingbird to the shape
  of the flower.

They help flowers do it, too!!!
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Once the pollen is delivered. . .
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But its not all about the pretty flowers. . .

• In addition to flowers, angiosperms improved
  their vascular system allowing them to survive in
  different terrestrial habitats
• Fiber cells specialized for support, and vessel
  elements of the xylem specialized for efficient
  water transport were added to the existing
  tracheids of the gymnosperms
• Sieve tube members improve the phloem

Tracheids are long and tapered while the vessel
elements are short and wide with perforated end
walls.
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• Trees became deciduous to prevent water loss in
  cold or dry weather (abscission)
• Double fertilization ensures the plant doesnt
  waste energy creating food stores for infertile
  ovules
• Roots and stems are modified for food or water
  storage

Leaves broadened in order to maximize
photosynthesis.