Evolution and Plant Diversity

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Evolution and Plant Diversity

• Chapter 29

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Evolution of Green Algae

• Plants share many characteristics with many
  protists
• Multicellular, eukaryotic,
• and photoautotrophs
• Cell walls of cellulose
• Chloroplasts with chlorophylls a and b
• Charophytes are only algae that share 4
  distinctive traits with land plants
• Identified lineage as closest relatives to land
  plants

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Charophytes Traits

• Rosette-shaped cellulose-synthesizing complexes
• Proteins in the PM that synthesize cellulose in
  cell wall
• Peroxisome enzymes
• Help minimize loss of organic products from
  photorespiration
• Flagellated sperm structure
• Similar structure in land plants with and
  charophyceans
• Formation of a phragmoplast
• Microtubules that form between daughter nuclei to
  create new cell wall in dividing cells
• Doesnt imply land plants are descendents

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Land Move Adaptations

• Charophyte algae inhabit shallow waters
• Dessication is a problem
• Natural selection chose individuals that could
  survive
• Sporopollenin is a polymer layer to prevent
  spores from drying out during dispersal
• Allowed 1st land plants to survive terrestrially
• Brighter sunlight, more CO2, and mineral rich
• Needed to overcome challenges
• Scarce water and little structural support
• 4 adaptations specific to land plants
• Not unique to (convergent evolution) and not all
  plants have

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Alternation of Generations

• Each generation gives rise to the other
• Gametophyte generation
• From 1n spore by mitosis
• Produce gametes by mitosis
• Gametes combine in syngamy to form 2n zygote
• Sporophyte generation
• From 2n zygote by mitosis
• Produces spores by meiosis
• Generations can look different
• Plants we see usually sporophyte

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Other Derived Traits
Apical meristems Localized regions of cell
division at tips of shoots and roots
Walled spores produced in sporangia. Multicell
ed organs where sporocytes (2n) produce spores
via meiosis.
Multicellular gametangia Archegonia female,
pear-shape with non-motile egg Antheridia male,
release sperm to environment
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Additional Characteristics

• Epidermis covered by a cuticle to protect leaves
  from desiccation
• Early plants without true roots and leaves
  benefited from mycorrhizal associations with
  fungi
• Review 2 types are?
• Secondary compound production to prevent against
  herbivores, parasites, and UV radiation
• Human source of spices and medicines
• E.g tannin in red wines from grape skin, stem,
  and seed responsible to dry, pucker
  taste/sensation of good reds

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Diversification of Plants

• Nonvascular unclear monophylogeny
• No vascular tissue, true roots, stems, or leaves
• Small, grow low, moist environments
• Vascular exist in smaller clades (phyla)
• Seedless are paraphyletic
• Seeds are embryos with nutrients in a protective
  shell
• Gymno naked seeds
• Angio flowering plants

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Nonvascular Plants

• Phylum Hepatophyta (liverworts)
• Marchantia has thalloid shape gametophyte
• Gametangia appear as mini trees from which
  sporophytes hang
• Plagiochilla has leafy looking gametophytes
• Phylum Anthocerophyta (hormworts)
• Long, tapered sporophyte with an open sporangium
• Gametophyte grows horizontally, 1st to colonize
  open area
• Phylum Bryophyta (mosses)
• Mainly see gametophyte stage, carpet-like
• Sporophytes visible and tall, green when young,
  tan to release spores

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Nonvascular Plants Life Cycle

• Gametophyte is dominant stages
• Protonemata produce buds
• Develop into gametophores with rhizoids anchors
• Antheridia or archegonia
• Can be bi- (not mosses)
• Sporophyte results
• Dependent on parent
• Develop foot, stalk (seta), and capsule
  (sporangium)

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Importance of Mosses

• Colonize bare, sandy soil and help retain
  nitrogen
• Moist environments and extreme ones
• Mountaintops, tundra, and deserts
• Survive despite loss of water and rehydrate when
  conditions improve
• Sphagnum forms deposits of dead organic material
  peat
• Good for water absorbing and gardening dried as
  fuel

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Evolution of Seedless Vascular Plants

• Sperm is flagellated like nonvascular plants so
  must move through films of water to fertilize egg
• Common in moist environments
• Branched sporophytes not dependent on
  gametophytes for nutrition
• Branching allowed for multiple sporangia
• Ancestors lacked roots, but shared other traits

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Seedless Vascular Plant Life Cycle

• Compare with nonvascular life cycle
• Sporophyte generation is larger and more complex
• In ferns is what is seen
• Gametophytes grow on or in soil
• Gametophytes reduced as evolution to seed plants

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Vascular Transport Tissue

• Xylem conducts most water and minerals
• Usess tracheids (tube-shaped cells) to move root
  to tip
• Cell walls strengthened with lignin, a polymer
• Phloem distributes sugars, amino acids, and other
  organics through cells arranged as tubes
• Evolutionary adaptations
• Taller
• Cover other plants (dominance)
• Evolution of trees

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Roots and Leaves Appear

• Roots absorb from the soil and provide support
• Resemble stem tissue
• Leaves increase SA and serve as photosynthetic
  organs
• Stomata to regulate gas and water exchange
• Microphylls small, spine-like leaves, single
  vascular tissue
• Phylum lycophyta only
• Megaphylls highly branched vascular tissue
• More photosynthetic
• Stems move water and minerals to leaves and
  organics from leaves to roots

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Sporophylls

• Modified leaves that bear sporangia
• Vary in structure between phyla of vascular
  plants
• Most seedless vascular plants are homosporous

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Phylum Lycophytes

• Club mosses, spike mosses, and quillworts
• Sporophylls clustered together as cone-like
  structures called strobili
• Club mosses all homosporous while others are
  heterosporous
• Club moss spores are rich in oil
• Photographers ignited them to create light

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• Previously represented as 3 separated phyla
• All homosporous
• Ferns
• Sporophytes produce fronds that grow as
  fiddlehead uncoils
• Gametophytes die after sporophyte detaches
• Horsetails
• Separate fertile (cone-bearing) and vegetative
  stems
• Stems have joints with small leaves emerging from
  them
• Stem is main photosynthetic organ
• Whisk ferns
• Sporophytes have branched stems, but no roots
• 3 fused sporangia on stems