EEB340 Lecture 8.docx

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10 Apr 2012
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Lecture 8: Evolution of Leaves
Evolution of Leaves
Leaf Types
Microphyll Enation Theory, Reduction Theory
Megaphyll Telome Theory
CO2 and leaf evolution in late Carboniferous
- leaf: lateral organ
o initiated at the shoot apical meristem
o determinant in growth (stop growth at certain point)
o have tissue systems (parenchymatous growth)
dermal tissue system
vascular tissue system
ground tissue system
- microphyll: develop on plants that have a protostele
o one main vein (are always exceptions maybe two veins)
o found in Lycophyta
- megaphyll: associated with all other stellar configurations
o complex vascular system
o evolution commonly described by Telome Theory
- in the fossil record, see microphylls in the Devonian (early)
o see megaphylls in the Late Devonian (later)
- Enation Theory: lateral perturbance from shoot apical meristem vascular tissue
grows through and into protrusion microphyll
o Microphyll isn’t necessarily small
- Reduction Theory: many branches coming off main stem with dichotomous
branching and protostele reduction in the maount of dichotomous branching
microphyll
o More favored by the fossil record and developmental biology
o Microphyll evolved by reduction in reproductive structures became sterile
o This reduction is common strategy applies to megaphylls (but no
protostele)
- In Carboniferous there were huge drops in CO2
- Mutation that increased stomatal density selected for because decreased CO2
density increased to 1000 mm-2
o Megaphyll will capture much more (200% more) solar energy as a planar
structure than will a radial structure
Will heat up much more
Can heat up to be 50-55 C must be cooled off couldn’t with
stomatal density of stem and this vascular system
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