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Ch. 21 Vascular Plants Without Seeds (The Megaphyll Line of Evolution:…

- - - - zygote undergoes only meiosis
- - - - both branches being equal in size and vigor
    - - fossils that have characters that include:
        
        characteristic of Cooksonia
    - - protostele
        
        center is solid mass of xylem with no pith
        
        endarch protostele
        
        prortoxylem located in center and metaxylem on edges of xylem mass
  - - - another group of early vascular plants named after Zosterophyllum
    - - outgrowths on surface
      - range of small to long, thin
- - - - enations in the division Lycophyta
  - - - culsters of extant lycophytes sporangia
  - - - small flap of tissue
      - distinguish selaginellas from lycopodiums
- - - - most important trend
      - unequal branching one stem more vigorous
    - - single main trunk
  - - - leaves evolved from branch systems
      - present in all seed plants, ferns, and equisetophytes
    - - telome theory
        
        megaphyll evolution
      - last dichotomy twigs
    - - sporangium-bearing, leaf-like structure
    - - all megaphyllous plants form a monophyletic clade
  - - - roots have exarch xylem
      - megaphylls
      - 30-kilobase inversion in large single-copy region of DNA
    - - two sister clades
    - - woody plants
  - - - 15 extant species
    - - ten sporangia located on this umbrella-shped
    - - main trunk
      - lateral branches
      - true leaves and roots
  - - - almost all of the monilophytes
    - - at each node
      - diverges from the siphonostele
    - - vascular cylinder of parenchyma
    - - clusters of sporangia where meiosis occurs
    - - eusporangium
        
        surface cells undergo periclinal divisions
      - leptosporangia
        
        initiated when single cell divides periclinally
        
        forms outward protrusion
- - - - lack seeds
      - reproduction is hidden