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Ferns

Ferns. Gymnosperms. Angiosperms. Gnetum. Description: (some apply to other Gnetales) Monoecious or dioecious

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Ferns

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  1. Ferns Gymnosperms Angiosperms

  2. Gnetum • Description: (some apply to other Gnetales) • Monoecious or dioecious • Stems woody (mainly vines), swollen nodes, vessels (up to 300 um) with vestured pits and fibers, high photosynthetic and transpiration capacities, syringaldehyde lignin, tunica presence outer apical meristem (1 cell wide not two) • Vessels derived from tracheids with circular pits (Angiosperms derived from tracheids with scalariform pits) • Leaves evergreen, opposite with reticulate venation and petioles, often drip tips, up to 10 cm wide • Fine venation is derived from fibers not vascular strands (Angiosperms)

  3. Gnetum • Description: (some apply to other Gnetales) • “Flowers” in strobili: Reduced megagametophytes, Double fertilization (but no endosperm), Possibly entomophily, Outer envelope encloses ovule • Seeds drupe like in brightly colored fleshy “fruit” • Cotyledons 2 and epigeal • Ectomycorrhizal

  4. Gnetum • But…sometimes gymnosperm like • Xylem can have tracheids with torus/margo pit • Root morphology • Circular border pitting

  5. Habitat • Gnetum: Tropical lowland rainforest • Ephedra: arid • Welwitschia: desert

  6. Distribution • 40 species: 10 S. America, 1 W. Africa, 20-25 Asia

  7. Historical biogeography • Won and Renner (2006): • Divergence began in late Oligocene to mid-Miocene (~25 mya) • Asian clades diverging in Miocene to Pliocene (4-22 mya) • When did Gondwana break up? (~200-250 mya) • African spp not a Gondwana relict! • Water dispersal is likely

  8. Gnetum • First evidence of horizontal gene flow (Won and Renner 2003) • Gnetum and the asterid Petunia (2-5 mya): nad1 intron 2

  9. Evolution of efficient xylem

  10. Evolution of efficient xylem

  11. Questions • Based on habit, xylem, and leaves, is Gnetum a weedy-disturbance specialist with fast photosynthetic and water transport rates? • Conducted field measures of hydraulic conductivity, photosynthesis and stomatal conductance in PNG with 2 tree and 2 liana Gnetum species (as well as a Podocarpaceae and 11 Angiosperms)

  12. Questions • Based on habit, xylem, and leaves, is Gnetum a weedy-disturbance specialist with fast photosynthetic and water transport rates? • Answer: No, actually performed similarly to Podocarpaceae, except for Gs (transpiration rates), Ks (sapwood specific conductivity), and HV (Huber value; sapwood area/leaf area) • Vessels and pinnate-veined leaves may allow for greater light capture and growth under low light

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