Abstract Detail



Paleobotany

Baresch, Andres  [1], Crifò, Camilla [2], Boyce, Charles [3].

Competition for epidermal space in the evolution of leaves with high physiological rates.

Leaves with high photosynthetic capacity also have high transpiration capacities, so that hydraulic conductance, stomatal conductance, and assimilation capacities should all be positively correlated. This is potentially problematic since these traits all make independent demands on anatomical space, particularly due to the propensity for veins to have bundle sheath extensions that are expressed on the epidermis as fields of cells where stomata are excluded. We measured the density and area occupation of bundle sheath extensions, the density, and size of stomata and their subsidiary cells, and venation density for a sample of extant canopy-reaching angiosperms expanded with similar measurements in fossil and living non-angiosperm tracheophytes. We found that space occupation conflicts are indeed important, even for low vein density plants. Whether vein density is high or low, even modest increases in vein density with the concomitant increases in stomatal conductance would require substantial reconfigurations of anatomy. This likely contributes to the stability in leaf architecture—and ecophysiology—seen through time in different lineages and contributes to the uniqueness of angiosperms in achieving the highest vein densities, stomatal densities, and physiological rates. In particular, flowering plants are distinguished by their capacity for small cell sizes and for hierarchical vein networks that allow expression of bundle sheath extensions in some, but not all of their veins, as opposed to the all-or-nothing alternatives required with the less-hierarchical vein networks seen in most non-angiosperms.


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1 - Stanford University, Geological Sciences, 450 Serra Mall Bldg 320, Stanford, CA, 94305, United States
2 - University Of Washington , Biology, PO BOX 351800, 24 Kincaid Hall, Seattle , WA, 98195, United States
3 - Stanford University, Geological Sciences, 450 Serra Mall, Bldg. 320, Stanford, CA, 94305, United States

Keywords:
Angiosperms
bundle sheath extensions
epidermis
Leaf anatomy
Stomata
vein density.

Presentation Type: Oral Paper
Number: 0001
Abstract ID:323
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award


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