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There is little evidence of the evolution of stomata in the fossil record, but they had appeared in land plants by the middle of the Silurian period.  They may have evolved by the modification of conceptacles from plants' alga-like ancestors.  However, the evolution of stomata must have happened at the same time as the waxy cuticle was evolving – these two traits together constituted a major advantage for early terrestrial plants. [ citation needed ]
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