Biology of Plants

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Chapter 17Seedless Vascular Plants
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Outline

• Evolution of vascular plants
• Organization of the vascular plant body
• Reproductive systems
• Phyla of seedless vascular plants
• P. Rhyniophyta (extinct)
• P. Zosterophllophyta (extinct)
• P. Trimerophytophyta (extinct)
• P. Lycopodiophyta
• P. Pterophyta

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Evolution of Seedless Vascular Plants

• Similarities btwn bryophytes and vascular plants
• alteration of heteromorphic generation
• Differences btwn bryophytes and vascular plants
• bryophytes
• dominant, free-living gametophyte
• nutritionally dependent sporophyte
• water-dependent reproduction b/c swimming sperm
• lack lignified vascular tissue (X and P)
• subapical meristem results in ? branching (1
  sporangium)
• vascular plants
• dominant, free-living sporophyte
• nutritionally dependent gametophyte
• lignified vascular tissue
• allows ? size b/c water transport rigid CW
• apical meristem allows ? branching (multiple
  sporangia)

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Evolution of Seedless Vascular Plants

• Trends in plant evolution
• mvmt from water to land
• increasing independence from water
• reproduction
• vascular tissues
• greater specialization via tissue differentiation
• 1st vascular plants little differentiation
• roots for anchorage, stems/lvs for Ps
• reduction of gametophytic generations
• seeds in one evolutionary line
• provide protection/nutrients
• Seedless vascular plants
• several phyla extinct
• 7 phyla w/ living representatives

Cooksonia 418 MYA
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Organization of the Vascular Plant Body

• Amandas Talk
• Terms
• root system, shoot system
• 3 tissue systems (dermal, vascular, ground)
• xylem and phloem
• 1 growth, tissues, plant body
• 2 growth, tissues, plant body
• vascular cambium, cork cambium, periderm
• tracheary elements, tracheids, vessel elements
• pith, stele, leaf traces, leaf gaps, leaf trace
  gaps
• protostele, siphonostele, eustele
• microphylls, megaphylls

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Reproductive System

• All vascular plants are oogamous and exhibit
  alteration of heteromorphic generations
  (sporophyte dominant)
• oogamous large, nonmobile egg and small, mobile
  sperm
• Vascular plants are homosporous or heterosporous
• homosporous 1 type of spore (equisetophytes,
  lycophytes, Pterophyta)
• spores produce bisexual gametophytes
• ferns functionally unisexual b/c different
  maturity times
• heterosporous 2 types of spores (lycophytes,
  Pterophyta, all seed plants), evolved later
• microspores produced in microsporangia become ?
  gametophyte (a.k.a. microgametophyte)
• megaspores produced in megasporangia become ?
  gametophyte (a.k.a. megagametophyte)
• unisexual gametophytes

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Reproductive System

• Gametophytes of homosporous plants
• larger, independent of sporophyte, photosynthetic
• Gametophytes of heterosporous plants
• smaller, dependent of sporophyte
• Evolutionary trend in vascular plants
• ? of gametophyte size/complexity
• mature megagametophytes of angiosperms 7 cells
  (1 egg)
• mature microgametophytes of angiosperms 3 cells
  (2 sperm)
• pollen grains microgametophytes of
  angio-/gymnosperms
• loss of archegonia and anthredia
• present in seedless vascular plants, absent in
  angiosperms
• archegonia present in gymnosperms but anthredia
  absent
• loss of swimming sperm
• instead wind, animal pollination

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Phyla of Seedless Vascular Plants

• Rhyniophyta/Zosterophyllophyta/Trimerophytophyta
  prominent during Devonian period (360 - 408 MYA)
• extinct
• Progymnospermophyta gives rise to seed plants
• 4 major groups of seedless vascular plants
• early vascular plants (Rhynio-/Zosterophyllo-/Trim
  erophytophyta)
• small, simple, primitive morphology, 370-425 MYA,
  extinct
• pteridophytes/lycophytes/progymnosperms
• more complex, 290-375 MYA
• seed plants
• 380 MYA, gymnosperms dominant until 100 MYA
• flowering plants
• 130 MYA, currently dominant

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Phylum Rhyniophyta

• 380-425 MYA, earliest known vascular plants
• Seedless, leafless, dichotomously branched
  stems, terminal sporangia
• Minimal differentiation of roots/stems/lvs
• Cuticle, stomata, epidermis, cortex,
  photosynthetic stems
• Vascular tissue similar to hydroids in mosses
• Homosporous
• Isomorphic generations
• Marshes
• Cooksonia
• oldest known vascular plant

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Phylum Zosterophyllophyta

• 370-408 MYA
• Leafless, dichotomously branched stems
• Laterally borne kidney-shaped sporangia
• Aerial parts covered w/ cuticle and stomata
• Downward branch similar to root
• Grass-like appearance
• Homosporous
• Ancestor of lycophytes

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Phylum Trimerophytophyta

• 395-415 MYA
• Evolved from Rhyniophyta
• Larger, ? complexity/specialization
• Leafless, dichotomously branched
• Large vascular strand
• thus ? ht
• Homosporous
• Ancestor of pteridophytes and
  progymnosperms

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Phylum Lycopodiophyta

• 10-15 living genera, 1200 sp.
• Descendants of zosterophylls
• Trees w/ woody/secondary growth or herbs
• Possess microphylls (small lvs)
• 400 MYA divergence of 2 clades
• lycophytes club mosses
• tree lycophytes dominant in Carboniferous
• euphllophytes ferns, horsetails, seed plants

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Family Lycopodiaceae

• 15 genera, 400 sp.
• Club moss (Lycopodium sp.)
• Artic to tropics, evergreen
• Rhizome w/ roots and stems
• Spiral microphylls
• Homosporous
• Sporangia borne on sporophylls
  (fertile microphyll)
• some sporophylls non-photosynthetic strobili
• conelike
• Bisexual gametes but cross fertilize
• 6 - 15 yrs for archegonia/anthredia mature
• Water required for fertilization - biflagellated
  sperm
• Independent sporophyte

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Family Selaginellaceae

• 1 genus, 750 sp.
• Tropics to deserts
• Selageniella resurrection plant
• become dormant when dry
• SW

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Family Selaginellaceae

• Microphylls, sporophylls and strobili
• Ligule small, scalelike outgrowth at base of
  sporophylls
• Heterosporous
• megasporangia borne by megasporophylls
• produce megaspores
• microsporangia borne by microsporophylls
• produce microspores
• mega- and microsporangia contained on single
  strobili
• Water necessary for fertilization (biflagellate
  sperm)
• Suspensor of embryo pushes embryo into
  gametophyte, which feeds off of gametophyte
  before becoming independent
• Gametophytes are unisexual
• growth w/i spores
• Nutritionally dependent sporophyte grows w/i
  gametophyte

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Family Isotaceae

• 1 genus (Isoetes), quillwort
• Sporophyte body
• underground stem w/ microphllys and roots
• Heterosporous w/ mega-/microsporophylls and
  spores
• Cambium produces 2º tissues w/ sieve
  elements/tracheids/ parenchyma
• Some obtain C from sediment,
  not atmosphere
• these lack stomata, have thick cuticle,
  minimal gas exchange w/
  atmosphere,
  CAM
• Black-spored Quillwort

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Phylum Pterophyta

• 11,000 sp., mostly in tropics
• Diversity of form/habit/size, some epiphytic
• Now includes Sphenophyta (horsetails)

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Phylum Pterophyta

• Homosporous or heterosporous
• 2 types of sporangia
• eusporangia multiple superficial initials
  (a.k.a. parent cells) involved in development of
  sporangia, results in inner and outer layers
• inner layer irregular mass, gives rise to spore
  mother cell
• outer layer sporangium wall

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Phylum Pterophyta

• leptosporangia 1 superficial initial
• results in stalked sporangium w/ capsule
  containing nutritive tissue (tapetum)
• tapetum gives rise to annulus
• each sporangia contains annulus
• annulus layer of cells that contracts to
  catapult spores
• inner tissue becomes spore mother cells ( 4
  spores)

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Phylum Pterophyta

• 4 types of ferns
• O. Ophioglossales and Marattiales (eusporangiate
  ferns)
• O. Ficales (homosporous leptosporangiate ferns)
• O. Marsileales and Salviniales (heterosporous
  leptosporangiate ferns)
• O. Psilotales (reduced fern)