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

- - - - earliest fossils that were vascular plants
      - equal dichotomous branching
        
        both branches being equal size and vigor
      - no separate microspores or megaspores
    - - center is a solid mass of xylem w no piths
    - - protoxylem is located in center
    - - metaxylem located in the center
  - - - outgrowths
      - ranged from small to long, thin scales
- - - - protecting clusters of sporangia
  - - - small flap of tissue
      - on upper surface of Selaginella leaves *
  - - - enations in the division Lycophyta
      - not the same as the leaves we're familiar w
- - - - also the lignophytes
        
        woody plants
  - - - horsetails
      - scourning rushes
    - - sporangia always occur in groups of 5 to 10
      - umbrella-shaped
    - - main trunk
      - lateral branches
      - true leaves
      - true roots
  - - - leaves that evolved from branch systems
      - present in all seed plants, ferns, and equisetophytes
    - - megaphyll evolution
    - - ultimate twig, last dichotomy
    - - all subdivisions of lateral branch aligned in 1 plane
    - - parenchyma develops between telomes and lower branches
    - - all megaphyllous plants form a monophyletic clade
  - - - leptosporangiate ferns
        
        the familiar ferns
    - - either vertical shoot
      - or horizontal rhizome
    - - located at each node
      - diverges from siphonostele
        
        then leaves a small segment of the vascular cylinder
        
        this region is the leaf gap
    - - underside of the leaf
      - clusters of sporangia where meiosis occurs
  - - - Psilophyton
      - Pertica
        
        pseudomonopodial branching
        
        single main trunk rather than series
      - Trimerophyton
    - - overtopping
        
        unequal branching where 1 stem was more vigorous