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Model for the evolution of Kranz-type C4 in dicots. A normal C3 dicot leaf is represented on the right. The endodermis/starch sheath (yellow) is present on the vasculature (blue) of the petiole and lower leaf zone, but is absent in the leaf blade/upper leaf zone. The hypothesized shift from C3 to Kranz-type C4 may arise when the endodermal/starch sheath program extends out from the petiole/lower leaf zone into the leaf blade.
