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This causes more transpiration to occur from lower leaf surface. What's the exact reason for why are there more stomatal openings on the lower surface of a dicot leaf?

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    $\begingroup$ I believe water conservation is the main reason. I'll try to write up a proper answer when I have time $\endgroup$ – C_Z_ May 12 '15 at 16:41
  • $\begingroup$ @CactusWoman Could you please post an answer if you have time now? :) $\endgroup$ – Gaurang Tandon May 29 '15 at 17:29
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Firstly, it is not necessary that all dicots have stomata on their lower surface of their leaves. The lotus Nelumbo nucifera has its stomata on its upper surface, due to the lower surface of its leaves being in contact with water, and therefore unable to transpire effectively.

The reason that stomata are usually on the lower surface has been analysed in this paper, which rejects the commonly held hypothesis that stomata appear on the lower surface of leaves (hypostomatous) as a response to dryness, by citing that hypostomatous leaves are relatively less common in dry environments.

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The paper then analyses the correlation observed between parameters of leaves and their stomatal locations.

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By using a number of computational models (which conclude that given the set of assumptions in the paper, leaves should not generally be hypostomatous), the paper addresses the faults of the model and concludes that there is no one single reason why leaves are usually hypostomatous, and then brings up a couple other possibilities that may help in explaining the majority of plants being hypostomatous.

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  • $\begingroup$ Wow! Great answer with proper source. Thank you! I will wait till 4th April for more answers (if anyone wants to post them), and then award the bounty to the best answer :) $\endgroup$ – Gaurang Tandon May 30 '15 at 4:34

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