TGP

• Tree


  Tall, has a woody stem (smaller woody plants = shrubs), monopodial growth (one trunk rather than many), apical dominance (grows upwards more quickly than branches grow outwards), secondary growth (trunk grows outward as well as upwards)
• Families of trees


  • Arecaceae - date palm
• Secondary thickening


  • A ring of dividing cells (meristem) just underneath the bark called the vascular cambium produces phloem on the outer side and xylem on the inner side
  • Sapwood = newer, outer xylem tissue (light-coloured), transporting water – lignified cells which are functionally dead
  • Heartwood = oldest, inner xylem, no transport, can rot away and not kill tree
  • Growth rings = seasonal growth
• Monocot stems


  Palm trees
• Trees are water fountains
• First trees evolved in the Northern hemisphere


  390Ma (Middle Devonian Period)
• Archaeopteris evolved in the Northern hemisphere


  380Ma (Late Devonian Period)
• Archaeopteris

  • Wood similar to conifers
  • Up to 8m tall, trunk diameter up to 1.5m
  • Still produced spores, not seeds
  • A progymnosperm
  • Formed vast, monodominant forests
• Giant clubmosses (Lepidodendron) evolved in the Northern hemisphere


  370-300Ma (Late Devonian to Upper Carboniferous)
• Lepidodendron


  • Sometimes wood, lots of structural bark
  • 10-35m tall, trunk diameter up to 1m
  • Produced spores, not seeds
  • A lycopsid (clubmoss)
  • Formed two-thirds of earliest tropical wetland forests
  • Full height in 10 years?
• Calamites and Medullosa evolved in the Northern hemisphere


  360-252Ma (Carboniferous-Permian)
• Calamites


  • Woody, lots of structural bark
  • Up to 18m tall, trunk diameter up to 1m
  • Produced spores, not seeds
  • A sphenopsid (horsetail)
  • Formed thickets between lycopsid trees, rather than understorey
• Conifers in all biomes

  Early Jurassic (206-180Ma)
• Angiosperm revolution around 100Ma, with more than 400,000 species of flowering plant today (compare with 750 species of seed plants), worldwide dominance by end-Cretaceous


  Late Cretaceous (72-66Ma)
• 95Ma in North America - huge angiosperm trees
• 66Ma in North America: Hell Creek Formation